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

This week roundup features a wide range of research topics from two current members of GARNet Advisory board as well as two papers featuring work from the lab of Laszlo Bogre at Royal Hollaway. The studies range from an investigation into the similarity between the barley and Arabidopsis circadian clocks, the role of MYR3R during regulation of organ growth, documenting a novel interaction of a MAPK protein and the development of new fluorescent probes for study of cysteine proteases.

 

Kusakina J, Rutterford Z, Cotter S, Martí MC, Laurie DA, Greenland AJ, Hall A, Webb AA (2015) Barley Hv CIRCADIAN CLOCK ASSOCIATED 1 and Hv PHOTOPERIOD H1 Are Circadian Regulators That Can Affect Circadian Rhythms in Arabidopsis. PLoS One. 10(6):e0127449. http://dx.doi.org/10.1371/journal.pone.0127449

This publication is the result of a multi-site collaboration between the Alex Webb at Cambridge, GARNet Advisory board member Anthony Hall at Liverpool, Andy Greenland at NIAB and David Laurie at the JIC. The focus of this study are the barley CIRCADIAN CLOCK ASSOCIATED 1 and PHOTOPERIODH1 genes, which are involved in regulation of the circadian clock. The authors investigated the circadian rhythms in barley whilst using heterologous expression in Arabidopsis to show that the barley CCA1 is functionally equivalent to AtCCA1 and that barley PHOTOPERIODH1 functions similar to AtPRR7.

 

Kobayashi K, Suzuki T, Iwata E, Nakamichi N, Suzuki T, Chen P, Ohtani M, Ishida T, Hosoya H, Müller S, Leviczky T, Pettkó-Szandtner A, Darula Z, Iwamoto A, Nomoto M, Tada Y, Higashiyama T, Demura T, Doonan JH, Hauser MT, Sugimoto K, Umeda M, Magyar Z, Bögre L, Ito M (2015) Transcriptional repression by MYB3R proteins regulates plant organ growth. EMBO J. http://dx.doi.org/10.15252/embj.201490899

GARNet advisory board member John Doonan and Royal Hollaway-based Laszlo Bogre are collaborators on this multi-nation publication that looked at the role of three MYB2R3 proteins in cell cycle control. Arabidopsis plants that have mutations in three repressor type-myb3r genes display enlarged organs. In addition, MYB3R3 binds to G2/M-specific genes and associates with the repressor-type E2F and RBR proteins. The authors perform a range of pair-wise interaction studies to identify components of multiprotein complexes, that have also been identified in other organisms. Ultimately they show that these MYC3R genes are important for periodic expression during the cell cycle and for establishing a post-mitotic quiescent state that determines organ size.

 

Kohoutová L1, Kourová H1, Nagy SK2, Volc J1, Halada P1, Mészáros T2,3, Meskiene I4,5, Bögre L6, Binarová P1 (2015) The Arabidopsis mitogen-activated protein kinase 6 is associated with γ-tubulin on microtubules, phosphorylates EB1c and maintains spindle orientation under nitrosative stress New Phytologist. http://dx.doi.org/10.1111/nph.13501

Laszlo Bogre also features as a collaborator in this East European-led study that investigated the interaction of the MAPK-protein MPK6 with microtubules. Immunoprecitations showed that the active form of MPK6 interacted with γ-tubulin, sedimenting with in vitro polymerised microtubules. In addition they identified a novel substrate for MPK6, the microtubule plus-end protein, EB1c. Overall the authors propose that MPK6 plays a significant role in maintaining regular planes of cell division, particularly during stress conditions.

 

Lu H, Chandrasekar B, Oeljeklaus J, Misas-Villamil JC, Wang Z, Shindo T, Bogyo M, Kaiser M, van der Hoorn RA (2015) Subfamily-specific Fluorescent Probes for Cys proteases Display Dynamic Protease Activities During Seed Germination. Plant Physiology http://dx.doi.org/10.1104/pp.114.254466

Renier Van De Hoorn who works in the Department of Plant Chemetics at the University of Oxford, leads this study that investigates the activity of plant cysteine proteases. They developed a novel set of fluorescent probes that specifically target different subfamilies of Cys proteases. In order to test these probes they used Arabidopsis mutant lines alongside transient expression studies in tobacco. In addition they show that these probes have broad applicable across 8 plant species. Finally they use these new tools to reveal the dynamic properties of different protease sub-families during remobilization of seed storage proteins in Arabidopsis.

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