GARNet Research Roundup: August 22nd

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Published on: August 22, 2018

This week’s GARNet research roundup highlights outstanding science from across the UK. First are a group of three papers led by researchers in Cambridge and Bristol that investigate the role of either sugar or calcium signaling on control of the plant circadian clock. Secondly is work from Durham that provides an elegant link between SUMOylation and the jasmonate-responsive arm of the defence response. The biotrophic arm of defence signaling is the focus of the next paper from University of Nottingham that investigates the role of the N-end rule pathway in that response. Finally is a paper from the John Innes Centre that identifies a key determinant of planar cell polarity across the Arabidopsis leaf.

Frank A, Matiolli CC, Viana AJC, Hearn TJ, Kusakina J, Belbin FE, Wells Newman D, Yochikawa A, Cano-Ramirez DL, Chembath A, Cragg-Barber K, Haydon MJ, Hotta CT, Vincentz M, Webb AAR, Dodd AN (2018) Circadian Entrainment in Arabidopsis by the Sugar-Responsive Transcription Factor bZIP63. Current Biol. doi: 10.1016/j.cub.2018.05.092

Open Access

This research comes from the labs of Anthony Dodd (University of Bristol) and Alex Webb (University of Cambridge) and is led equally by Alexander Frank, Cleverson Matioli, Americo Viana, Timothy Hearn and Jelena Kusakina. They investigate how the Arabidopsis circadian clock is entrained to respond to changing metabolic rhythms, measured by assessing sugar signaling. The molecular factors that control changes in the circadian oscillator were previously unknown but they show that the transcription factor BASIC LEUCINE ZIPPER63 (bZIP63) is required to alter expression of the oscillator gene PSEUDO RESPONSE REGULATOR7 (PRR7). They also show that the SnRK1 sugar sensing kinase and TREHALOSE-6-PHOSPHATE SYNTHASE1 (TPS1) gene are required for sugar-mediated circadian adjustment. This study provides important information about additional layers of regulation controlling the relationship between the circadian clock and plant metabolism.

Martí Ruiz MC, Hubbard KE, Gardner MJ, Jung HJ, Aubry S, Hotta CT, Mohd-Noh NI, Robertson FC, Hearn TJ, Tsai YC, Dodd AN, Hannah M, Carré IA, Davies JM, Braam J, Webb AAR (2018) Circadian oscillations of cytosolic free calcium regulate the Arabidopsis circadian clock. Nat Plants. 2018 Aug 20. doi: 10.1038/s41477-018-0224-8

This second paper from the labs of Alex Webb and Anthony Dodd also features work from Isabelle Carre’s and Julia Davis’s lab in Warwick and Cambridge respectively. This work led by María Carmen Martí Ruiz, Katharine Hubbard and Michael J. Gardner looks at the how oscillations of cytoplasmic calcium influence the central circadian clock. They show that calcium influences the clock through the activity of the CALMODULIN-LIKE24 (CML24) gene and further genetic analysis links these activities through the action of the central clock gene TIMING OF CAB2 EXPRESSION1 (TOC1). This paper is also a clear lesson in persistence as it was first received by Nature Plants back in May 2016.

Ohara T, Hearn TJ, Webb AAR, Satake A. Gene regulatory network models in response to sugars in the plant circadian system. J Theor Biol. doi: 10.1016/j.jtbi.2018.08.020

The research includes members of Alex Webb’s group and develops a theoretical model to predict the response of the gene regulatory network that links the circadian clock to metabolic signals. This model predicts that the targets of sugar signaling could be both members of the PSEUDO-RESPONSE REGULATOR gene family as well as evening complex components. These findings are experimental confirmed in the paper by Frank et al in this edition of the GARNet response roundup.

Srivastava AK, Orosa B, Singh P, Cummins I, Walsh C, Zhang C, Grant M, Roberts MR, Anand GS, Fitches E, Sadanandom A (2018) SUMO Suppresses the Activity of the Jasmonic Acid Receptor CORONATINE INSENSITIVE 1. Plant Cell. doi: 10.1105/tpc.18.00036

Open Access

Lead author on this paper from the labs of Elaine Fitches and Ari Sadanandom at the Unversity of Durham is Anjil Kumar Srivastava and includes co-authors from Lancaster University. In the study they reveal a feedback loop between the jasmonic acid receptor CORONATINE INSENSITIVE 1 (COI1) and its targets for degradation; the JASMONATE ZIM (JAZ) domain-containing repressor proteins. The authors show that SUMOylated JAZ proteins inhibit the COI1-dependent degradation of non-SUMOylated JAZ proteins. In addition they identify a SUMO-responsive element within the COI1 protein and that necrotrophic bacteria specifically target SUMO protease in order to modulate JA-responsive defense responses.

Vicente J, Mendiondo GM, Pauwels J, Pastor V, Izquierdo Y, Naumann C, Movahedi M, Rooney D, Gibbs DJ, Smart K, Bachmair A, Gray JE, Dissmeyer N, Castresana C, Ray RV, Gevaert K, Holdsworth MJ (2018) Distinct branches of the N-end rule pathway modulate the plant immune response. New Phytol. doi: 10.1111/nph.15387

Open Access
Jorge Vicente leads this work from the lab of Mike Holdsworth in Nottingham that includes collaborators from Belgium, Spain, Germany and Austria. They investigate the role of the N-end rule degradation pathway in the plant immune response. Indeed they show that portions of this response mediated by the E3 ligase PROTEOLYSIS (PRT)6 are important for expression of a specific set of defense-related genes and basal resistance to a biotropic pathogen. They also show this response is also important in the monocot barley where plants with reduced expression of HvPRT6 have enhanced resistance to different pathogens.

Mansfield C, Newman JL, Olsson TSG, Hartley M, Chan J, Coen E (2018) Ectopic BASL Reveals Tissue Cell Polarity throughout Leaf Development in Arabidopsis thaliana. Curr Biol. doi: 10.1016/j.cub.2018.06.019

Open Access
Catherine Mansfield leads this study from the lab of Enrico Coen at the John Innes Centre that investigates the factors that control cell polarity during leaf development. They show that BASL (BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE) is essential for establishment an organ-wide polarity field across the Arabidopsis leaf. They show this polarity field is aligned with the proximodistal axis of the leaf (base to tip) and is independent of stomatal patterning. Like in animals this demonstrates that planar plant organs have a tissue-wide cell polarity field that might be critical for guiding growth and differentiation.

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