Arabidopsis Research Roundup: August 27th

The Arabdopsis Research Roundup broadens its remit this week. As well as including three original research papers, which look at casparian strip formation, light and hormone signaling, we also highlight an important viewpoint article that aims to set standards for synthetic biology parts. In addition we include a meeting report from a plant synthetic biology summer school and interviews with plant scientists at the JIC, Caroline Dean and Anne Osbourn.

Kamiya T, Borghi M, Wang P, Danku JM, Kalmbach L, Hosmani PS, Naseer S, Fujiwara T, Geldner N, Salt DE (2015) The MYB36 transcription factor orchestrates Casparian strip formation Proc Natl Acad Sci USA http://dx.doi.org/10.1073/pnas.1507691112 Open Access

GARNet Advisory Board Chairman David Salt (Aberdeen) leads this international collaboration that looks at the (relatively) poorly understood Casparian strip (CS), a lignin-based filter that lies in root endodermal cells. Formation of the CS is initiated by Casparian strip domain proteins (CASPs) that recruit other proteins, which begin the process of lignin deposition. In this study the authors look upstream this process and identify the transcription factor MYB36 that directly regulates expression of CASPs and is essential for CS formation. Ectopic expression of MYB36 in root cortical tissues is sufficient to stimulate expression of CASP1-GFP and subsequent deposit a CS-like structure in the cell wall of cortex cells. These results have implications for the design of future experiments that aim to control how nutrients are taken up by the plant as even though myb36 mutants have a ‘root-defect’, they also have changes to their leaf ionome.

Sadanandom A, Ádám É, Orosa B, Viczián A, Klose C, Zhang C, Josse EM, Kozma-Bognár L, Nagy F (2015) SUMOylation of phytochrome-B negatively regulates light-induced signaling in Arabidopsis thaliana Proc Natl Acad Sci USA http://dx.doi.org/10.1073/pnas.1415260112 Open Access

Ari Sadanandom (Durham) and Ferenc Nagy (Edinburgh) are the leaders of this study that investigates the precise function of the PhyB photoreceptor protein. PhyB interacts with a wide range of downstream signaling partners including the PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors. The small ubiquitin-like modifier (SUMO) peptide is conjugated to larger proteins to bring about a variety of signaling outcomes. In this case the authors find that SUMO is preferentially attached to the C-term of PhyB under red light conditions, a relationship that occurs in a diurnal pattern. SUMOylation of PhyB prevents interaction with PIF5 whilst the OVERLY TOLERANT TO SALT 1 (OTS1) protein likely de-SUMOlyates PhyB in vivo. Altered levels of PhyB SUMOylation cause distinct light-responsive phenotypes and as such this paper adds another level of regulation to the already complex known network that controls light signaling.

Schuster C, Gaillochet C, Lohmann JU (2015) Arabidopsis HECATE genes function in phytohormone control during gynoecium development Development. http://dx.doi.org/10.1242/dev.120444 Open Access

Christopher Schuster who is now a postdoc based at the Sainsbury lab in Cambridge is the lead author on this investigation into the role of the HECATE (HEC) family of bHLH transcription factors on fruit development in Arabidopsis. During this process HEC proteins are involved in the response to both the phytohormones auxin and cytokinin, the authors proposing that HEC1 plays an essential role in Arabidopsis gynoecium formation.

Patron N et al (2015) Standards for plant synthetic biology: a common syntax for exchange of DNA parts New Phytologist http://dx.doi.org/10.1111/nph.13532 Open Access

Carmichael RE, Boyce A, Matthewman C Patron N (2015) An introduction to synthetic biology in plant systems New Phytologist http://dx.doi.org/10.1111/nph.13433 Open Access

Although not strictly based on Arabdopsis work, there are a couple of articles in New Phytologist that have broad relevance to plant scientists who are interested in plant synthetic biology. In the first of these Nicola Patron (The Sainsbury Laboratory) leads a wide consortium that aims to set parameters for the standardisation of parts in plant synthetic biology. It is hoped that as the principles of synbio are used more widley in the plant sciences that the proposals in this paper will serve as a useful guide to standidise part production. GARNet has recently written a blog post on this topic.
SynBioWorkshopPic
The associated meeting report looks at the use of plant synthetic biology in a teaching context with a synopsis of the ERASynBio summer school hosted by John Innes Centre. In this event, young researchers from a range of backgrounds were introduced to the power and potential of plant synthetic biology through a diverse course of lectures, practical session and group projects.

 

Vicente C (2015) An interview with Caroline Dean Development http://dx.doi.org/10.1242/dev.127548 Open Access

An interview with Anne Osbourn (2015) New Phytologist <a href="http://dx.doi acheter cialis.org/10.1111/nph.13616″ onclick=”_gaq.push([‘_trackEvent’, ‘outbound-article’, ‘http://dx.doi.org/10.1111/nph.13616’, ‘http://dx.doi.org/10.1111/nph.13616 ‘]);” target=”_blank”>http://dx.doi.org/10.1111/nph.13616 Open Access

These are interviews with eminent female plant molecular biologists who both work at the John Innes Centre. Caroline Dean’s lab focuses on the epigenetic mechanisms that regulate vernalisation whilst Anne Osbourn is interested in using synthetic biology approaches to engineer metabolic pathways for the production of novel compounds.

Arabidopsis Research Roundup: July 30th

Two broad topics dominant the studies featured in this weeks Arabidopsis Research Roundup. Environmental and hormonal factors that control different types of ‘dormancy’ are presented in studies from the labs of Caroline Dean (JIC) and Ian Graham (York). Elsewhere two Sainsbury lab (Norwich) led studies investigate different aspects of the interaction between plants and bacterial pathogens. Finally Colin Turnbull from Imperial College is involved in an interesting assessment of cytokinin concentrations across the root tip.

Duncan S, Holm S, Questa J, Irwin J, Grant A, Dean C (2015) Seasonal shift in timing of vernalization as an adaptation to extreme winter Elife. http://dx.doi.org/10.7554/eLife.06620

Caroline Dean (JIC) again publishes in the open access journal eLife as her lab continues to investigate the precise detail of the vernalisation response. This response shows natural variation that is dependent on the geographic distribution of Arabidopsis ecotypes. Plants collected from northern latitudes showed maximum vernalisaton at 8oC, both at the level of flowering time and FLC chromatin silencing. The vernalisation response was measured both in controlled and field conditions and all Northern ecotypes were importantly shown to vernalise prior to snowfall, which would allow flowering immediately after thawing. These findings have important implications for models aimed at predicting the affect of climate change on flowering time.

Ibarra SE1, Tognacca RS1, Dave A2, Graham IA2, Sánchez RA1, Botto JF (2015) Molecular mechanisms underlying the entrance in secondary dormancy of Arabidopsis seeds Plant Cell Environ http://dx.doi.org/10.1111/pce.12607

Ian Graham is the leader of the Centre for Novel Agricultural Products (CNAP) at the University of York and contributes to this Argentinian-led study that looks into the molecular factors that underlie secondary dormancy in Arabidopsis seeds. They show that this process involves changes in the content and sensitivity to GA (but not ABA) that requires the activity of the RGL2 protein acting through ABI5. A wide geographical study then perhaps unsurprisingly showed that temperature is also an important variable influencing the induction of secondary dormancy

Lee D, Bourdais G, Yu G, Robatzek S, Coaker G (2015) Phosphorylation of the Plant Immune Regulator RPM1-INTERACTING PROTEIN4 Enhances Plant Plasma Membrane H+-ATPase Activity and Inhibits Flagellin-Triggered Immune Responses in Arabidopsis Plant Cell http://dx.doi.org/10.1105/tpc.114.132308

Silke Robatek (TSL) is the UK lead on this collaboration with UC-Davis that looks at phosphorylation of RPM1-INTERACTING PROTEIN4 (RIN4) in a range of Arabidopsis genotypes that are suspectible to infection. Flexibility of the RIN4 protein is affected by phosphorylation and this causes enhanced suspectibility coincident with increasing plasma membrane H+-ATPase activity. The expression of the AHA1 ATPase is high in guard cells and therefore linked to stomatal opening. As such bacterial infection works to phosphorylate RIN4 that in turn increases the chance of bacterial entry.

Pfeilmeier S, Saur IM, Rathjen JP, Zipfel C, Malone JG (2015) High levels of cyclic-di-GMP in plant-associated Pseudomonas correlate with evasion of plant immunity Mol Plant Pathology http://dx.doi.org/10.1111/mpp.12297

GARNet Advisory Board Member Cyril Zipfel (TSL) and Jacob Malone (JIC) investigate the response to pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) by the plant innate immune system. The resulting pattern-triggered immunity (PTI) fends off pathogen attack by recognition of bacterial flagellin by, amongst others, the FLAGELLIN SENSING2 (FLS2) protein. In this study the authors focus on the bacterial side of the response and show that cyclic-di-GMP is involved in the evasion of PTI, although this also reduces virulence, likely due to reduced flagellar motility. This results in a trade off for the bacteria in which it is not recognised as readily by plant yet isn’t as virulent.

Antoniadi I, Plačková L, Simonovik B, Doležal K, Turnbull C, Ljung K, Novák O (2015) Cell-Type-Specific Cytokinin Distribution within the Arabidopsis Primary Root Apex Plant Cell http://dx.doi.org/10.1105/tpc.15.00176

Colin Turnbull (Imperial College) is a contributor to this Swedish-Czech collaboration that measures cytokinin concentrations in root cell files isolated by FACS and analysed by MS. The authors show a gradient of cytokinin across the root tip with maximum concentrations in the lateral root cap, columnella and QC cells. As these are also areas of high auxin concentration, the authors suggest that this implies that interactions between the two hormone groups are cell type specific.

Arabidopsis Research Roundup: July 20th

There is a bumper crop of publications in high quality journals in this weeks UK Arabidopsis Research Roundup, including manuscripts in PNAS, Nature Communications, PLoS Genetics , PloS One and Plant Physiology. Malcolm Bennett, Alex Webb and Anthony Hall lead a major collaborative effort that links the circadian clock with lateral root formation whilst Ottoline Leyser (SLCU) and Mike Bevan (JIC) participate in a similarly broad consortium in a study linking organ size and MAPK signaling. Liam Dolan’s group from Oxford looks at mechanisms of tip-growth across the plant kingdoms whilst elsewhere three members of faculty at the University of Birmingham are involved in two papers looking at the regulation of meiosis. Finally there are two US-led studies that include significant contributions from UK-based researchers, including Matthew Jones from the University of Essex.

 

Voß U, Wilson MH, Kenobi K, Gould PD, Robertson FC, Peer WA, Lucas M, Swarup K, Casimiro I, Holman TJ, Wells DM, Péret B, Goh T, Fukaki H, Hodgman TC, Laplaze L, Halliday KJ, Ljung K, Murphy AS, Hall AJ, Webb AA, Bennett MJ (2015) The circadian clock rephases during lateral root organ initiation in Arabidopsis thaliana Nature Communication 6:7641. http://dx.doi.org/10.1038/ncomms8641

Once again Malcolm Bennett (CPIB) leads a multi-Institute collaboration that includes Alex Webb (Cambridge) and current GARNet board member Anthony Hall (Liverpool). This is also an extremely international effect with groups from the UK, USA, Sweden, Japan, Spain and France. The science looks at lateral root stems cells and how the circadian clock is rephased during LR emergence. They show that the clock controls auxin levels and auxin-related genes. The conclusion is that the circadian clock acts to gate auxin signalling during LR development to facilitate organ emergence and adds to a growing portfolio of evidence that suggest the circadian clock might act in a cell autonomous manner. Anthony Hall, James Locke and Peter Gould currently have a grant that is looking at this phenomenon in Arabidopsis root cells.

 

Johnson KL, Ramm S, Kappel C, Ward S, Leyser O, Sakamoto T, Kurata T, Bevan MW, Lenhard M (2015) The Tinkerbell (Tink) Mutation Identifies the Dual-Specificity MAPK Phosphatase INDOLE-3-BUTYRIC ACID-RESPONSE5 (IBR5) as a Novel Regulator of Organ Size in Arabidopsis PLoS One.10(7):e0131103. http://dx.doi.org/10.1371/journal.pone.0131103

Ottoline Leyser, Sally Ward (Sainsbury lab, Cambridge) and Mike Bevan (JIC) are the UK contributors to this joint UK-German-Japanese-Australian collaboration. This study follows a screen for plants with reduced organ size and introduces a novel allele of the dual-specificity MAPK phosphatase INDOLE-3-BUTYRIC ACID-RESPONSE5 (IBR5), named Tinkerbell (tink). This mutation reveals that IBR5 is a novel regulator of organ size by changing the growth rate in petals and leaves although this occurs independent of the previously characterised KLU pathway. The authors use microarray data to suggest an additional role for TINK/IBR5 during male gametophyte development. Ultimately they conclude that IBR5 might influence organ size through auxin and TCP growth regulatory pathways.

 

Tam TH, Catarino B, Dolan L (2015) Conserved regulatory mechanism controls the development of cells with rooting functions in land plants Proc Natl Acad Sci U S A. http://dx.doi.org/10.1073/pnas.1416324112

Liam Dolan’s lab at the University of Oxford is a world leader in the study of root hair development. Previously it has been shown the group XI basic helix-loop-helix (bHLH) transcription factor (LOTUS JAPONICUS ROOTHAIRLESS1-LIKE (LRL) regulates root hair growth in Arabidopsis, Lotus or rice. This study investigates the equivalent proteins in the moss Phycomitrella patens and show that they are involved in an auxin signaling pathway that promotes cell outgrowth albeit via a different set of signaling intermediates. Overall the authors show that a core auxin network that supports cellular ‘tip-growth’ exists throughout land plant lineages even though the specificity of this signaling has diverged over the course of the ~420million years that separates angiosperms and mosses.

 

Varas J, Sánchez-Morán E, Copenhaver GP, Santos JL, Pradillo M (2015) Analysis of the Relationships between DNA Double-Strand Breaks, Synaptonemal Complex and Crossovers Using the Atfas1-4 Mutant. PLoS Genet.11(7): e1005301. http://dx.doi.org/10.1371/journal.pgen.1005301

The work led by Monica Pradillo at the University of Madrid includes a contribution from Eugenio Sanchez-Moran from the University of Birmingham. This work focuses on the hetero-trimeric Chromatin Assembly Factor 1 (CAF-1), which is a histone chaperone that assembles acetylated histones H3/H4 onto newly synthesized DNA. In Arabidopsis the CAF1 complex is composed of the FAS1, FAS2 and MSI1 proteins. Atfas1 mutant plants are less fertility, have a higher number of double stranded breaks (DSB) and show a higher gene conversion frequency. The authors investigate how DSBs can influence meiotic recombination and synaptonemal complex (SC) formation by genetic analysis of Atfas1-containing double mutants. Ultimately their experiments provide new insights into the relationships between different recombinase proteins in Arabidopsis. Overall an increase in the number of DSBs does not translate to an increase in the number of crossovers (COs) but instead in a higher GC frequency. The authors provide different theories to explain this mechanism, including the possible existence of CO homeostasis in plants.

 

Lambing C, Osman K, Nuntasoontorn K, West A, Higgins JD, Copenhaver GP, Yang J, Armstrong SJ, Mechtler K, Roitinger E, Franklin FC (2015) Arabidopsis PCH2 Mediates Meiotic Chromosome Remodeling and Maturation of Crossovers PLoS Genetics 11(7):e1005372 http://dx.doi.org/10.1371/journal.pgen.1005372

The University of Birmingham is the lead Instiution in this study that also investigates regulation of meiosis. The groups of Chris Franklin and Sue Armstrong collaborate with US and Austrian partners to study the organization of meiotic chromosomes during prophase I. Using structured illumination microscopy (SIM) they show that dynamic changes in chromosome axis is coincident with synaptonemal complex (SC) formation and depletion of the ASY1 protein, which requires the function of the PCH2 ATPase. Using a pch2 mutant the authors are able to tease apart different aspects of ‘crossover’ (CO) biology and that the pch2 defect occurs precisely during CO maturation, not during designation. In addition, CO distribution is also affected in some chromosome regions showing that failure to deplete ASY1 can result in downstream events that include disruption of CO patterning.

 

Jones MA, Hu W, Litthauer S, Lagarias JC, Harmer S (2015) A Constitutively Active Allele of Phytochrome B Maintains Circadian Robustness in the Absence of Light Plant Physiology. http://dx.doi.org/pp.00782.2015

Matthew Jones (University of Essex) is the primary author of this work that comes from a collaboration from his time in the lab of Stacey Harmer in UC Davis. Since 2012 Matthew has been a lecturer at the University of Essex where he continues with work of this nature. In this study they introduce a constitutively active allele of the PHYB photoreceptor that is able to phenoopy red-light input into the circadian clock. In these mutants the pace of the clock is insensitive to light-intensity and this response is dependant on its PHYB nuclear localisation. Finally they show that fine tuning of PHYB signalling requires PHYC and overall they conclude that nuclear phytocrome signalling is necessary for sustaining clock function under red light.

 

Chakravorty D, Gookin TE, Milner M, Yu Y, Assmann SM (2015) Extra-Large G proteins (XLGs) expand the repertoire of subunits in Arabidopsis heterotrimeric G protein signalling Plant Physiol. http://dx.doi.org/10.1104/pp.15.00251

Sally Assman from Penn State University leads this study that includes a contribution from Matthew Milner who now works at NIAB. The number of proposed G protein subunits is greatly reduced in diploid plant genomes yet this study shows that a family of Arabidopsis GPA-related proteins (XLG1-3) can increase the repertoire of potential G proteins interactions by interacting with beta and gamma subunits. The authors propose they have uncovered a new plant-specific paradigm in cell signaling.

Arabidopsis Research Roundup: July 11th

A couple of weeks since the last update as it’s been quiet for UK Arabidopsis Research publications. However we now see a variety of publications that address some important questions in different signaling pathways. Firstly a multinational collaboration performs a genome-wide analysis of DELLA binding, followed by two studies looking different aspects of light signaling, specifically the link with the production of protective carotenoids and also with the tight control of protein degradation. Elsewhere there is the description of a systems biology approach developed to aid the definition of signaling pathways in non-model organisms and finally a commentary piece about some work on Arabidopsis Arenosa.

 

Genome Wide Binding Site Analysis Reveals Transcriptional Coactivation of Cytokinin-Responsive Genes by DELLA Proteins (2015) Marín-de la Rosa N, Pfeiffer A, Hill K, Locascio A, Bhalerao RP, Miskolczi P, Grønlund AL, Wanchoo-Kohli A, Thomas SG, Bennett MJ, Lohmann JU, Blázquez MA, Alabadí D PLoS Genet. 11(7):e1005337. http://dx.doi.org/10.1371/journal.pgen.1005337

The Centre for Integrative Biology in Nottingham and Rothamstead Plant Science partner with groups from Sweden, Germany, Spain and Saudi Arabia in this truly international collaboration. They investigate the role of DELLA proteins in the relay of environmental cues to multiple transcriptional circuits. The primary experimentation in this study uses ChIP-Seq to analyse the DNA-binding sites of one DELLA protein. Perhaps as expected the DELLA protein binds multiple promotor regions yet with a particular enrichment in regions upstream of cytokinin-regulated genes, where they interact with type-B ARABIDOPSIS RESPONSE REGULATOR (ARR) proteins. The biological relevance of this mechanism is underpinned by the requirement for both DELLAs and B-type ARRs in the control of root growth and photomorphogenesis.

 

Regulation of carotenoid biosynthesis by shade relies on specific subsets of antagonistic transcription factors and co-factors (2015) Bou-Torrent J, Toledo-Ortiz G, Ortiz-Alcaide M, Cifuentes-Esquivel N, Halliday KJ, Martinez-Garcia JF, Rodriguez-Concepcion M Plant Physiol.

Karen Halliday at the University of Edinburgh is part of this UK-Spanish team that studied the regulation of carotenoid biosynthesis via a light signaling module formed by PIF1 and HY5. In shade conditions, PIF proteins signal for a decrease in carotenoid accumulation, thus saving the plant unneeded energy consumption. The PIF1 response focusses on the phytoene synthase (PSY) biosynthetic gene and is antagonised by the PAR1 transcriptional co-factor. However this is not a universal response carried out by known antagonisers of PIF1 function, demonstrating that carotenoid biosynthesis is finely regulated by a precise subset of regulatory proteins.

 

High-level expression and phosphorylation of phytochrome B modulates flowering time in Arabidopsis (2015) Hajdu A, Ádám É, Sheerin DJ, Dobos O, Bernula P, Hiltbrunner A,, Kozma-Bognár L, Nagy F Plant Journal http://dx.doi.org/10.1111/tpj.12926

Professor Ferenc Nagy has dual appointments in Edinburgh and in Hungary and this output results from work performed in Hungary. This study looks at control of flowering via phytochrome B signalling, which has been previously shown to rely on the degradation of the CONSTANS (CO) protein that in turn delays flowering by attenuating FLOWERING LOCUS T (FT) expression. Therefore phyB mutants show accelerated flowering, yet this is unexpectedly also true following PHYB overexpression. The novelty of this study comes from showing that PHYB overexpression induces FT without affecting CO transcription but rather acts by causing accumulation of the CO protein, due to an affect on a COP1-ubiquitin ligase complex. This article adds further detail to the already complex relationship between light signaling, the circadian clock, protein degradation and de novo transcription in the control of flowering in Arabidopsis.

 

Inferring orthologous gene regulatory networks using interspecies data fusion (2015) Penfold CA, Millar JB, Wild DL. Bioinformatics. 31(12):i97-i105. http://dx.doi.org/10.1093/bioinformatics/btv267

This study was led by David Wild from Warwick Systems Biology Centre. The authors have used two related Bayesian approaches to network inference that allow Gene Regulatory Networks (GRN) to be jointly inferred in, or leveraged between, several related species, for example between Arabidopsis and related crop species. Inferring gene function is achieved with more accuracy when GRNs are compared between species rather than attempting to use stand alone inference. The manuscript uses data from the yeast S.pombe but the broader principles could be applied to other experimental systems.

 

The High Life: Alpine Dwarfism in Arabidopsis (2015) Bomblies K Plant Physiol. 168(3):767. http://dx.doi.org/10.1104/pp.15.00745

This commentary piece about high altitude growth of Arabidopsis aernosa is the first published work from Kristen Bomblies since she moved her lab to the John Innes Centre from Havard (together with the lab of Levi Yant). Having these two talented young researchers relocate to the UK is be great for UK plant science so I sure everyone in the community wishes them all the best. Watch Kristen talk about her work at a New Phytologist conference from 2014.

Levi Yant also has two postdoctoral posts currently available in his lab.

 

Arabidopsis Research Roundup: June 10th.

This weeks UK Arabidopsis Research Roundup features work from two members of the GARNet advisory board who are working on very different aspects of how plants response to external stimuli. In addition there is a genetic and biochemical dissection of primary cell wall formation as well as a comment piece that questions recent findings concerning the relationship between auxin, ABP1 and cortical microtubules.

Busoms S, Teres J, Huang X, Bomblies K, Danku J, Douglas A, Weigel D, Poschenrieder C, Salt DE (2015) Salinity is an agent of divergent selection driving local adaptation of Arabidopsis thaliana to coastal habitats Plant Physiology http://dx.doi.org/pp.00427.2015

Current GARNet Chairman David Salt from Aberdeen has collaborated with researchers from Spain, Germany and the USA in this study that looks at the drivers of adaptive evolution of Arabidopsis plants grown in saline conditions. Unusually this is a field-based study using Arabidopsis that naturally grow in coastal or inland areas of NE Span. Plants taken from coastal areas outperform inland plants when grown on highly saline soils, indicating local adaptation to salt tolerance. The authors conclude that the variation in sodium concentration is causing divergent selection between these two populations.

Monaghan J, Matschi S, Romeis T, Zipfel C (2015) The calcium-dependent protein kinase CPK28 negatively regulates the BIK1-mediated PAMP-induced calcium burst Plant Signaling and Behaviour June 2015 http://dx.doi.org/10.1080/15592324.2015.1018497

GARNet advisory board member Cyril Zipfel from the Sainsbury lab led this study looking at the role of the cytoplasmic kinase BIK1 in the plants response to microbial infection. In plants that are mutant for the Ca2+-dependent protein kinase CPK28, BIK1 accumulates, which leads to enhancing immune signaling. In this study the authors add to these previous finding from their lab by showing that CPK28 also contributes to a burst of Ca2+ production following exposure to pathogens.

Mortimer JC, Faria-Blanc N, Yu X, Tryfona T, Sorieul M, Ng YZ, Zhang Z, Stott K, Anders N, Dupree P (2015) An unusual xylan in Arabidopsis primary cell walls is synthesised by GUX3, IRX9L, IRX10L and IRX14 Plant Journal http://dx.doi.org/10.1111/tpj.12898

Paul Dupree from the Biochemistry department at the University of Cambridge led this work that investigated a newly characterised form of Xylan, a little studied component of the plant primary cell wall. Genetic analysis indicates that the IRX9L, IRX10L and IRX14 proteins are necessary for xylan backbone synthesis. Importantly this new xylan is contains GlcA side chains, whose addition only requires the glucuronyltransferase GUX3. This type of xylan has not been observed in secondary cell walls so the authors comment on how differences in xylan structure assist in the formation of primary vs secondary cell walls.

Taken from wikipedia.
Taken from wikipedia.

 

 

 

 

 

T Baskin (2015) Auxin inhibits expansion rate independently of cortical microtubules. Trends in Plant Science http://dx.doi.org/10.1016/j.tplants.2015.05.008

Visiting scholar at CPIB in Nottingham, Tobias Baskin provides a short reply to a publication in Nature that claimed that the control of cell expansion by auxin is caused by reorientation of cortical microtubules. In this paper, Tobias provides evidence from both a simple experiment and from the literature that this might not be the paradigm-shifting observation that it initially appears.

Arabidopsis Research Roundup: June 3rd 2015

We are unashamedly biased in this weeks Arabidopsis Research Roundup which firstly features work from the group of GARNet PI Jim Murray about the genetic interactions that define growth of lateral organs. Elsewhere we highlight papers that investigate a different role for CYCD3 genes in vascular development, the role of TFL1 in the shoot meristem and the ability of Arabidopsis seedling to tolerant a high light environment during ontogenesis.

Randall RS, Sornay E, Dewitte W, Murray JA (2015) AINTEGUMENTA and the D-type cyclin CYCD3;1 independently contribute to petal size control in Arabidopsis: evidence for organ size compensation being an emergent rather than a determined property Journal Experimental Botany http://dx.doi.org/10.1093/jxb/erv200

Jim Murray and Walter Dewitte (Cardiff) lead this study that investigates the relationship between the AINTEGUMENTA (ANT) transcription factor and cyclin CYCD3;1 during lateral aerial organ (LAO) formation. LAO growth is determined by the both the number and size of cells that comprise the organ. During petal development, ant mutants have reduced cell number but increased cell size, demonstrating a ‘compensatory mechanism’ of growth. In contrast cycd3;1 mutants have increased cell size that results in larger petals, showing no compensatory mechanism. Interestingly ant cycd3;1 double mutants do show growth compensation in the same tissue. The authors propose that occurrence of the compensatory mechanism depends on at which time-point during distinct phases of cell division and cell expansion the growth defect occurs.

 

C Collins, Maruthi M.N and C Jahn (2015) CYCD3 D-type cyclins regulate cambial cell proliferation and secondary growth in Arabidopsis. Journal Experimental Botany http://dx.doi.org/10.1093/jxb/erv218

Another study that investigates a different role of D-type cyclins is led by former Murray lab member, Carl Collins working at the Natural Resources Institute at the University of Greenwich. The factors that control cambial cell growth are poorly understood but the authors provide a link between the cell cycle and cambial differentiation by showing that CYCD3 subgroup of genes play a role in the process. Three CYCD3 genes are expressed in cambial tissue and the equivalent triple mutant has reduced hypocotyl and stem diameter, which is linked to a reduction in mitotic activity. Conversely, mutant xylem cells increased in size. This shows that CYCD3 genes provide a mechanism for controlling the correct proportions of cell growth during vascular development. This might provide a useful tool in the future study of this important process in woody plants.

 

Carvalho FE, Ware MA, Ruban AV (2015) Quantifying the dynamics of light tolerance in Arabidopsis plants during ontogenesis Plant Cell Environment http://dx.doi.org/10.1111/pce.12574

The group of Professor Alexander Ruban at Queen Marys University London utilise a novel methodology to measure the ‘intactness’ of photosystem II (PSII). In this paper they assess the amount of light required to inhibit PSII activity through the life cycle of Arabidopsis plants grown in short days. They show that maximum light tolerance occurs in 8-week old plants. Interestingly the light tolerance correlates with rates of electron transport yet did not coincide with the chlorophyll a/b ratios or anthocyanin content.

 

Baumann K, Venail J, Berbel A, Domenech MJ, Money T, Conti L, Hanzawa Y, Madueno F, Bradley D (2015) Changing the spatial pattern of TFL1 expression reveals its key role in the shoot meristem in controlling Arabidopsis flowering architecture. Journal Experimental Botany http://dx.doi.org/10.1093/jxb/erv247

The TFL1 gene is a repressor of flowering in the Arabidopsis shoot meristem. Researchers from the UK, USA, Spain and Italy, led by Desmond Bradley at the JIC show that ecoptocally expressed TFL1 can repress flowering outside of its normal expression domain. By comparing the expression of TFL1 with genes that determine floral identity (APETALA, LEAFY) the authors conclude that the shoot meristem is more sensitive to TFL1, allowing the maintenance of a vegetative state in this tissue.

Great British Success in ERA-CAPS

The ERA-CAPS funding call was a major EU initiative that was focused on plant sciences. Recently the second set of successfully funded projects were announced, even though the funding levels have not been confirmed. Amongst these twelve successful bids, eight feature UK plant scientists (including four from the JIC). These successful projects are highlighted below:
logo-era-caps
Project Name: DesignStarch, Designing starch: harnessing carbohydrate polymer synthesis in plants

The UK representative Rob Field is a biochemist based at the John Innes Centre. The objective of this project is to ‘gain a profound understanding of the regulation and control of the biophysical and biochemical processes involved in the formation of the complex polymeric structure that is the starch granule’, which will involve in vitro analysis of the enzymology of starch formation with the ultimate aim of transferring their findings back into plants.

EfectaWheat: An Effector- and Genomics-Assisted Pipeline for Necrotrophic Pathogen Resistance Breeding in Wheat

James Cockram (NIAB) is the project leader on this grant that proposes to investigate the economically important wheat leaf spot group (LSG) of necrotrophic pathogens. The project will use a range of techniques such as high-density genotyping, pathogen re-sequencing and advanced virulence diagnosis to deliver a genomics- and effector-based pipeline for the genetic dissection of LSG host-pathogen interactions across Europe.

EVOREPRO: Evolution of Sexual Reproduction in Plants

Both David Twell (Leicester) and Jose Gutierrez-Marcos (Warwick) are included in this seven-group consortium that aims to investigate the origin of the mechanisms that predate double fertilization in plants. The project will take a comparative gene expression-based approach to investigate gametogenesis across Marchantia, Physcomitrella, Amborella, Arabidopsis and a range of crop species. The expected findings will allow the identification of specific mechanisms that are targeted by environmental stresses during sexual reproduction in crops and will assist in the selection of stress-resistant cultivars.

INTREPID: Investigating Triticeae Epigenomes for Domestication

GARNet advisory board member Anthony Hall (Liverpool) leads this group which includes long time collaborator Mike Bevan (JIC). This project will look at variations in the epigenome across eight diverse wheat lines with the aim of determined how epigenetic marks are re-set and stabilized during the formation of new wheat hybrids and how they might influence gene expression.

MAQBAT: Mechanistic Analysis of Quantitative Disease Resistance in Brassicas by Associative Transcriptomics

John Innes Centre scientist Chris Ridout leads this six PI consortium that will look at pathogen resistance in Brassica napus, where diseases are a major limiting factor in growth success. Almost 200 lines of B.napus will be screened against a range of specific and general pathogens in the aim of discovering important disease resistance loci. One proposed aspect of the work will look at the role of glucosinolates in both disease resistace and seed quality. The project also includes UK B.napus expert Bruce Fitt (Hertfordshore).

PHYTOCAL: Phytochrome Control of Resource Allocation and Growth in Arabidopsis and in Brassicaceae crops

Karen Halliday (Edinburgh) leads this three-PI group that will investigate the link between phytochrome signaling and resource allocation in both Arabidopsis and B.rapa. One aim of the project will be to build models that predict the dual action of phytochrome and photosynthesis on resource management and biomass production.

RegulaTomE: Regulating Tomato quality through Expression

Cathie Martin (JIB) leads this largest successful consortium of 8 labs that aim to link transcriptional regulation of metabolic pathways with tomato quality. Loci contributing to abiotic stress tolerance will also be identified toward the combined goals of obtaining more nutritious, stable and sustainable crops. The project will lead to regulatory gene identification (an important advance in terms of fundamental understanding), and provide new tools for metabolic engineering of fruit quality.

SOURSI: Simultaneous manipulation of source and sink metabolism for improved crop yield

Lee Sweetlove (Oxford) leads this group that aims to understand the linkages between source and sink tissues in the assimilation of carbon and nitrogen. The project claims to implement a metabolic engineering strategy of unprecedented scale in plants exploiting the new technique of biolistic combinatorial co-transformation.

Arabidopsis Research Roundup

Categories: Arabidopsis, GARNet, Global, UKPSF
Comments: No Comments
Published on: May 14, 2015

Your UK Arabidopsis Research Round-up this week contains studies that aim to define a network of lateral root formation, elucidate modes of calcium signaling, determine mechanisms of epigenetic memory and also the influence of exon-edge evolution in determining the extent of selective pressure.

Liu J, Whalley HJ, Knight MR. Combining modelling and experimental approaches to explain how calcium signatures are decoded by calmodulin-binding transcription activators (CAMTAs) to produce specific gene expression responses. New Phytologist. 2015 Apr 27. doi: 10.1111/nph.13428.

Marc Knight’s group at the University of Durham have attempted to decode the complex mechanism by which calcium controls changes in gene expression. They have developed an experimentally parameterized model that reveals calcium signals are amplified by the binding of calmodulin and calmodulin-binding transcription activators (CAMTAs). Interestingly, the model suggests that gene expression change in response to a calcium signature is defined by the previous history of that signal.

Lavenus J, Goh T, Guyomarc’h S, Hill K, Lucas M, Voß U, Kenobi K, Wilson MH, Farcot E, Hagen G, Guilfoyle TJ, Fukaki H, Laplaze L, Bennett MJ. Inference of the Arabidopsis Lateral Root Gene Regulatory Network Suggests a Bifurcation Mechanism That Defines Primordia Flanking and Central Zones. Plant Cell. 2015 May 5. pii: tpc.114.132993.

The biology of lateral root (LR) formation has been well researched over the past decade although a full robust regulatory network that controls this process has remained elusive. CPIB at the University of Nottingham, together with European collaborators have used a series of transcriptomic datasets to develop a time-delay correlation algorithm (TDCor) to infer the gene expression network (GRN) controlling LR initiation. The GRNs associated with AUXIN RESPONSE FACTOR7 and ARF5 predict a mutual inhibition and a patterning mechanism that controls flanking and central zone specification of LR primordia.

Berry S, Hartley M, Olsson TS, Dean C, Howard M Local chromatin environment of a Polycomb target gene instructs its own epigenetic inheritance. Elife. 2015 May 8;4. doi: 10.7554/eLife.07205.

Epigenetic ‘memory’ allows plant cells to retain a memory of past environmental or development events. One key regulator of this process is the Polycomb Repressive Complex2 (PRC2). Histone proteins that are modified by the PRC2 can be inherited through cell division. The groups of Mark Howard and Caroline Dean at the JIC investigated whether this inheritance directs long term memory in a cis or trans manner. Two copies of the Arabidopsis FLC gene, which is a target for PRC2, were monitored in the same plant. Interestingly they reveal that one FLC copy could be silenced but the other remained active, providing evidence that epigenetic memory, at least of FLC, is stored in trans but not in cis.

Bush SJ, Kover PX, Urrutia AO. Lineage-specific sequence evolution and exon edge conservation partially explain the relationship of evolutionary rate and expression level in A. thaliana. Mol Ecol. 2015 Apr 30. doi: 10.1111/mec.13221.

Alongside genetic changes in response to phenotypic adaptation, the elements of a genes DNA structure can also affect evolutionary rates. In Arabidopsis the ‘edge’ of exons, which flank introns and contain splice enhancers are known to have a higher degree of evolutionary conservation compared to coding regions. Dr Arazi Urrutia and collaborators from the University of Bath assessed selective pressure (measured by dN/dS) and showed that exon edge conservation partially explains the relationship between rates of protein evolution and expression level. Without any consideration of exon-edge conservation can potentially increase the number of genes designated as being under adaptive selection. Therefore the authors conclude that exon-edge conversation should be an important consideration when assessing overall dN/dS ratios.

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