Bumping into a hole understanding of auxin signaling

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Published on: January 24, 2018

The cellular mechanics of auxin perception and signaling have been well studied over the past two decades. The pivotal interaction that controls this activity involves the auxin-dependent contact between the TIR1 receptor and a family of transcriptional regulators called AuxIAA proteins. This interaction has been characterised at a structural level with the auxin indole-3-acetic acid (IAA) shown to act as a ‘molecular glue’, stabilising the interaction between TIR1 and the AuxIAA. This subsequently causes the degradation of the AuxIAA protein, setting off a cascade of auxin-dependent transcriptional responses.

Revealing the precise kinetics of this interaction is complicated by the fact that TIR1 belongs to a family of six related receptors and the AuxIAA family comprises 29 members. Although IAA is able to mediate the interaction between each of these family members, the TIR1 auxin binding pocket is somewhat promiscuous, with a wide range of auxin analogues being able to illicit a similar responses.

In order to develop a synthetic auxin signaling complex that was free from the complexities of varying protein family interactions, Keiko Torii and co-workers from the University of Washington and Nagoya University employed a bump-and-hole strategy. This technique sits at the interface of chemistry, biology and engineering and in this case was able to create a functional synthetic receptor-substrate interaction that did not interfere with the endogenous activity of TIR1-AuxIAA. This research has been published in Nature Chemical Biology.


Using the bump-and-hole strategy the authors interrogated the TIR1 auxin binding-pocket, predicting that removal of a bulky phenylalanine would result in a ‘hole’ whose space could be filled by a version of IAA that included an aryl-ring ‘bump’.

The authors showed that this ‘concave (ccv) TIR1’ was able to interact with the ‘convex (cvx) IAA’ and remarkably be able to elicit a biological relevant response in vivo. Generation of transgenic plants expressing ccvTIR1 or the application of exogenous cvxIAA has little effect on plant growth. However in the presence of cvxIAA, these ccvTIR1 transgenic plants show alterations in primary root elongation, lateral root development and gene expression changes characteristic of an auxin response. Therefore this paper synthetically replicated the auxin signaling module, whose function absolutely relies upon the presence of both components.

This research is a superb example for the use of modeling and synthetic chemistry to facilitate the study of a complex biological system. There is no doubt that the ccvTIR1-cvxIAA system is an important tool for study of the cellular auxin response as well for the tissue-specific activities of this do-it-all phytohormone. We await the development of an engineered enzyme that can produce cvxIAA in vivo so that the system will not need to rely on any external additions!!!

Arabidopsis Research Roundup: January 23rd.

This weeks Arabidopsis Research Roundup begins with two papers from Royal Hollaway University of London that investigate the factors that control leaf development in the dark and the control of PIN1 phosphorylation. Third is a paper from Bristol that demonstrates the translation of research from Arabidopsis into coriander with regard the control of the response to UV light. Next is research from the John Innes Centre that characterises the role of DNA methylation during meiosis in the male lineage.

Christine Foyer (Leeds) leads the next paper that defines the relationship between cold treatment and strigolactone signalling. The penultimate paper is led by Richard Napier from the University of Warwick and determines the parameters that define the substrates of the AUX1 protein whilst the final paper includes Cyril Zipfel (TSL) as a co-author and uses systems biology approaches to characterise the interactions between leucine-rich repeat receptor kinases (LRR-RKs).

Mohammed B, Farahi Bilooei S, Doczi R, Grove E, Railo S, Palme K, Ditengou FA, Bögre L, Lopez-Juez E (2017) Converging energy and hormonal signalling control meristem activity, leaf initiation and growth Plant Phys doi: 10.1104/pp.17.01730


Open Access

Enrique Lopez-Juez (RHUL) leads this collaboration with German and Hungarian colleagues that investigates the fundamental question; ‘Why don’t leaves grow in the dark’. They show that this response is influenced by both auxin transport and the plants energy sensing mechanisms. Interestingly when energy is provided via external sucrose, leaves develop differently in the dark than they do in the light indicating that multiple signaling pathways differentially influence this phenotype.

Enrique discusses this paper on the GARNet YouTube page.

Dory M, Hatzimasoura E, Kállai BM, Nagy SK, Jäger K, Darula Z, Nádai TV, Mészáros T, López-Juez E, Barnabás B, Palme K,,, Bögre L, Ditengou FA,,, Dóczi R (2017) Coevolving MAPK and PID phosphosites indicate an ancient environmental control of PIN auxin transporters in land plants. FEBS Lett. doi: 10.1002/1873-3468.12929

Laszlo Bogre and Enrique Lopez-Juez (RHUL) are co-authors on this Hungarian-led study that has discovered 3 conserved putative MAPK sites within the auxin transport protein PIN1. Phosphorylation of two of these sites causes partial loss of PIN1 membrane localization and therefore opposes the effect of the PINOID kinase, whose activity promotes PIN1 membrane localisation.


Fraser DP, Sharma A, Fletcher T, Budge S, Moncrieff C, Dodd AN, Franklin KA (2017) UV-B antagonises shade avoidance and increases levels of the flavonoid quercetin in coriander (Coriandrum sativum). Sci Rep. doi: 10.1038/s41598-017-18073-8 Open Access

Keara Franklin and Anthony Dodd (University of Bristol) lead this collaboration between academic researchers and those in the company Vitacress. They translate research from Arabidopsis into Coriander that looks at the effect of UV-B on stem elongation and the interaction with flavonoid signaling. This work shows that alterations to the UV-B regime during growth of potted herbs might reduce deleterious effects caused by neighbour proximity.

Walker J, Gao H, Zhang J, Aldridge B, Vickers M, Higgins JD, Feng X (2017) Sexual-lineage-specific DNA methylation regulates meiosis in Arabidopsis. Nat Genet. doi: 10.1038/s41588-017-0008-5

Xiaoqi Feng (JIC) is the corresponding author on this collaboration with James Higgins from Leicester and they investigate the role of DNA methylation in the control of male meiosis. They demonstrate that RNA-directed DNA methylation (RdDM) in the male lineage regulates gene expression in meiocytes and results in the mis-splicing of the MPS1/PRD2 transcipt, which causes aberrant alterations in spindle formation.

Cooper JW, Hu Y, Beyyoudh L, Yildiz Dasgan H, Kunert K, Beveridge CA, Foyer CH (2018) Strigolactones positively regulate chilling tolerance in pea and in Arabidopsis. Plant Cell Environ. doi: 10.1111/pce.13147

Christine Foyer (Leeds) is the corresponding author on this collaboration with Australian, Turkish and South African colleagues that looks into the role strigolactones play during chilling tolerance in both Arabidopsis and pea plants. Plants that have been chilled during the night have reduced biomass, which was not observed in either pea or Arabidopsis strigolactone mutants. This demonstrates a clear role for this hormone in this response and provides a potential target for the manipulation of plant growth under environmental conditions.

Hoyerova K, Hosek P, Quareshy M, Li J, Klima P, Kubes M,, Yemm AA, Neve P, Tripathi A, Bennett MJ, Napier RM (2017) Auxin molecular field maps define AUX1 selectivity: many auxin herbicides are not substrates. New Phytol. doi: 10.1111/nph.14950


Together with Czech co-authors Richard Napier (Warwick University) leads this investigation into the mode of action of the AUX1 auxin influx carrier and its substrate preferences. This work made use of a novel auxin accumulation assay and associated mathematical modeling to describe the parameters that make difference auxins to be good candidates for the AUX1 transport. Interesting they find that many commonly used auxinicide herbicides are poor substrates for AUX1 and the relevance of this finding for herbicide management strategies.


Smakowska-Luzan E et al (2018) An extracellular network of Arabidopsis leucine-rich repeat receptor kinases. Nature doi: 10.1038/nature25184

Cyril Zipfel (TSL) is a co-author on this US-European study that performs a systems-biology analysis on the possible interactions between extracellular domains of the leucine-rich repeat receptor kinases (LRR-RKs) gene family in Arabidopsis. Analysis of 40K potential interactions allows the generation of a LRR-based cell surface interaction network (CSI-LRR). This was used to discover previously uncharacterized interactions between LRR-RKs and to demonstrate that these interactions allow the translocation of extracellular signals in balanced and tightly regulated patterns.

Enrique Lopez-Juez (RHUL) talks to GARNet

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Published on: January 17, 2018

Enrique Lopez-Juez (Royal Holloway University of London) introduces a paper from that attempts to answer a critical question in plant science ‘Why do plants makes leaves in the dark‘?



Arabidopsis Research Roundup: January 10th 2018

This Arabidopsis Research Roundup covers the final papers of 2017 and the first of this new year. The initial paper is led by researchers in Bristol and characterises how the multifaceted BIG protein influences stomatal dynamics in response to altered CO2. Second is a manuscript from SLCU that for the first time in plants demonstrates nuclear sequestration of cell cycle regulated mRNAs.

Next is a paper from Rothamsted that describes a role for the hormone GA during floral development. David Salt (Nottingham) is then a co-author on a manuscript that has determined a role for the CTL protein in ion homeostasis.

Seth Davies from York is the lead author on the next study that investigates a link between metabolism and the circadian clock. The sixth paper looks at genes involved in the control of autophagy and features Patrick Gallois (Manchester) as a co-author.

There are three papers from researchers working on Norwich Research Park with Cyril Zipfel (TSL) involved in a study that looks at vacuolar trafficking of BR signaling components. Janneke Balk leads a study that characterises enzymes involved in biosynthesis of metal co-factors whilst the final NRP-based paper from Nick Pullen and Steven Penfield (John Innes Centre) describes the Leaf-GP open software for automated plant phenotyping.

The penultimate paper uses a set of PlantProbes (developed by Paul Knox at Leeds) to study pollen development whilst the final paper from Keith Lindsey (Durham) describes the application of a Bayesian statistical methodology to model the parameters that control a hormone signaling network.

He J, Zhang RX, Peng K, Tagliavia C, Li S, Xue S, Liu A, Hu H,, Zhang J, Hubbard KE,, Held K, McAinsh MR, Gray JE, Kudla J, Schroeder JI, Liang YK, Hetherington AM (2018) The BIG protein distinguishes the process of CO2 -induced stomatal closure from the inhibition of stomatal opening by CO2. New Phytol. doi: 10.1111/nph.14957 Open Access

Alistair Hetherington (University of Bristol) leads this UK-USA-China collaboration that has characterised a role for the mysterious BIG protein during stomatal closure in response to altered CO2 concentration. Interestingly BIG mutants do not show a defect in stomatal opening in response to altered CO2, allowing the dissection of this complex response through the activity of this protein. It remains to be determined exactly how the BIG protein influences this process.

Yang W, Wightman R, Meyerowitz EM (2017) Cell Cycle Control by Nuclear Sequestration of CDC20 and CDH1 mRNA in Plant Stem Cells. Mol Cell. doi: 10.1016/j.molcel.2017.11.008

Elliott Meyerowitz (SLCU) is the corresponding author of this research that provides the first characterisation in plants of nuclear sequestration of mRNAs from developmental important genes. The authors show that Arabidopsis anaphase-promoting complex/cyclosome (APC/C) coactivator genes CDC20 and CCS52B are confined to the nucleus in prophase, preventing translation of the cognate proteins until metaphase, which appears to protect cyclins from degradation at an inappropriate phase of the cell cycle

Plackett ARG, Powers SJ, Phillips AL, Wilson ZA, Hedden P, Thomas SG4 (2017) The early inflorescence of Arabidopsis thaliana demonstrates positional effects in floral organ growth and meristem patterning. Plant Reprod. doi: 10.1007/s00497-017-0320-3

This study is led from Rothamsted Research and includes Zoe Wilson from the University of Nottingham. They perform a systematic analysis of early floral organ initiation across the Arabidopsis inflorescence, discovering that both GA-dependent and independent stages are important for this process, albeit via the activity of presently unknown factors.

Gao YQ, Chen JG, Chen ZR An D, Lv QY, Han ML, Wang YL, Salt DE, Chao DY (2017) A new vesicle trafficking regulator CTL1 plays a crucial role in ion homeostasis. PLoS Biol. doi: 10.1371/journal.pbio.2002978

Open Access

David Salt (University of Nottingham) is a co-author on this Chinese-led investigation into the role of the vesicle trafficking regulator choline transporter (CTL) during the control of ionome homeostasis. Using ctl1 mutants they show that this function is required for the action of certain ion transporters as well as during plasmodesmata (PD) development. This study provides novel insights into the role of vesicular transport in the control of ion homeostasis and how the location of these ions might alter vesicle activity.

Sánchez-Villarreal A, Davis AM, Davis SJ (2017) AKIN10 Activity as a Cellular Link Between Metabolism and Circadian-Clock Entrainment in Arabidopsis thaliana.

Plant Signal Behav. doi: 10.1080/15592324.2017.1411448

Seth Davies (University of York) is the corresponding author on this study demonstrating that overexpression of the AKIN10 subunit of the SnRK1 complex results in increased period length of the circadian clock. The authors postulate about the possible links between metabolic rate and function of the clock, allowing them to present a model of action that features each of the central regulatory elements.

Havé M, Balliau T, Cottyn-Boitte B, Dérond E, Cueff G, Soulay F, Lornac A, Reichman P, Dissmeyer N, Avice JC, Gallois P, Rajjou L, Zivy M, Masclaux-Daubresse C (2017) Increase of proteasome and papain-like cysteine protease activities in autophagy mutants: backup compensatory effect or pro cell-death effect? J Exp Bot. doi: 10.1093/jxb/erx482

Open Access
This study is led by French researchers and includes Patrick Gallois (University of Manchester) as a co-author. The work focuses on the role of the ATG genes during autophagy, the key process that controls nutrient recycling during senescence. In atg5 mutants they show that different sets of proteases are misregulated, suggestive of a complex relationship between the enzymes involved in nutrient remobilization.

Liu Q, Vain T, Viotti C, Doyle SM, Tarkowská D, Novák O, Zipfel C, Sitbon F, Robert S, Hofius D (2017) Vacuole Integrity Maintained by DUF300 Proteins Is Required for Brassinosteroid Signaling Regulation. Mol Plant. doi: 10.1016/j.molp.2017.12.015

Cyril Zipfel (TSL) is a member of this Pan-European consortium that investigates the role of the vacuolar proteins, LAZARUS1 (LAZ1) and LAZ1 HOMOLOG1 (LAZ1H1) on the cellular cycling of BR-signaling components. Plants with mutations in laz1 and laz1h1 show increased BAK1 accumulation at the tonoplast as well as enhanced BRI1 trafficking and degradation. These DUF300 proteins appear to play a specific role in BR signalling as other vacuolar-associated proteins are not involved in this process.

Kruse I, Maclean A, Hill L, Balk J (2017) Genetic dissection of cyclic pyranopterin monophosphate biosynthesis in plant mitochondria. Biochem J. doi: 10.1042/BCJ20170559 Open Access

Janneke Balk (John Innes Centre) leads this study that has identified novel alleles in mitochondrial enzymes that are involved in the biosynthesis of metal cofactors. Analysis of these enzyme mutant reveals that they show deficiencies in the synthesis of cyclic pyranopterin monophosphate (cPMP), revealing fresh insights into the metabolic processes involving this key intermediate.

Zhou J, Applegate C, Alonso AD, Reynolds D, Orford S, Mackiewicz M, Griffiths S, Penfield S, Pullen N (2017) Leaf-GP: an open and automated software application for measuring growth phenotypes for arabidopsis and wheat. Plant Methods. doi: 10.1186/s13007-017-0266-3

Open Access

Nick Pullen and Steve Penfield (John Innes Centre) introduce this new software tool for the automated measurement of plant phenotypes. This Leaf-GP software is open access and has the sophistication to discriminate between different aspects of both Arabidopsis and greenhouse growth wheat.

This paper is back of a special issue of Plant Methods that is based on the use of Computer Vision in Plant Phenotyping.

Ndinyanka Fabrice T, Vogler H, Draeger C, Munglani G, Gupta S, Herger AG, Knox JP, Grossniklaus U, Ringli C (2017) LRX Proteins play a crucial role in pollen grain and pollen tube cell wall development. Plant Physiol. doi: 10.1104/pp.17.01374

Open Access

This Swiss-led study looks into the role of LRX proteins during cell wall formation and how they affect pollen germination and pollen tube formation. The authors took advantage of the molecular tools produced by Paul Knox (University of Leeds) as part of his Plant Probes project.

Vernon I, Liu J, Goldstein M, Rowe J, Topping J, Lindsey K (2017) Bayesian uncertainty analysis for complex systems biology models: emulation, global parameter searches and evaluation of gene functions. BMC Syst Biol. doi: 10.1186/s12918-017-0484-3 Open Access

Keith Lindsey (University of Durham) leads this paper that applies a Bayesian statistical methodology to analyse a model of hormonal crosstalk in the Arabidopsis root. They show that this technique can provide new insight into the behavior of models and enables the identification of new interesting rate parameters.

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