5th Nov 2015

Academics from the John Innes Centre lead two of the papers featured in this week Arabidopsis Research Roundup. Firstly Veronica Grieneisen leads a study that combines modeling and experimental work to assess the factors that establish the root auxin maximum and secondly the structural biologist David Lawson heads up an investigation into the plastid-localised enzyme, DPE1. Seemingly a common theme in UK-Arabidopsis research focuses on the factors that control the dynamics of stomatal opening and this week Mike Blatt from Glasgow heads a team that investigates the role of potassium and nitric oxide in this process. Finally we present a paper that investigates proteins that interact within the ER.

El-Showk S, Help-Rinta-Rahko H, Blomster T, Siligato R, Marée AF, Mähönen AP, Grieneisen VA (2015) Parsimonious Model of Vascular Patterning Links Transverse Hormone Fluxes to Lateral Root Initiation: Auxin Leads the Way, while Cytokinin Levels Out PLoS Comput Biol. e1004450 Open Access

Veronica Grieneisen (JIC) is the UK-based leader of this work that was performed with her Finnish collaborators. They work on the modeling the processes that define the auxin maximum in the root meristem. This patterning is defined by the activity of the PIN-formed auxin efflux transport proteins and the AHP6 protein, an inhibitor of cytokinin signaling. The authors implement a parsimonious computational model of auxin transport that considers hormonal regulation of the auxin transporters within a spatial context, explicitly taking into account cell shape and polarity and the presence of cell walls. They initially find that variation in cytokinin signaling, mediated by diffusion of the hormone is insufficient for patterning but rather it is an auxin-dependent modification of the cytokinin signal that can define the auxin maximum. Although the role that the PIN proteins play in root vascular patterning is well established, the authors experimentally verify a role for the AUX/LAX auxin influx carrier family of proteins. They also show that polar PIN localisation generates a flux of auxin flow that ultimately causes its own accumulation in the pericycle cells that signal for lateral root initiation. Finally their model confirms the supposition that these pericycle cells compete for auxin accumulation, therefore ensuring that lateral roots develop in the correct localisation. The associated figure is from this paper.

O'Neill EC, Stevenson CE, Tantanarat K, Latousakis D, Donaldson MI, Rejzek M, Nepogodiev SA, Limpaseni T, Field RA, Lawson DM (2015) Structural Dissection of the Maltodextrin Disproportionation Cycle of the Arabidopsis Plastidial Enzyme DPE1. Journal of Biological Chemistry Open Access

This is another paper led by JIC researchers, this time in collaboration with Thai partners. This focuses on determining the structure of the Arabidopsis Plastidial Disproportionating Enzyme 1 (DPE1) that acts to convert two maltotriose molecules to a molecule of maltopentaose and a molecule of glucose, which, for different reasons, are both more functional useful molecules for the plant. They have used ligand soaking techniques to trap the DPE1 in a different set of conformational states and have found that it exists as a homodimer with a variety of interesting features. This includes a dynamic ‘gate’ loop that may play a role in substrate capture, subtle changes in which could alter the efficacy of the active site. The structural insights provided by this study allow the authors to confidently delineate the complete AtDPE1 disproportionation cycle

Chen ZH, Wang Y, Wang JW, Babla M, Zhao C, García-Mata C, Sani E, Differ C, Mak M, Hills A, Amtmann A, Blatt MR (2015) Nitrate reductase mutation alters potassium nutrition as well as nitric oxide-mediated control of guard cell ion channels in Arabidopsis New Phytol. Open Access

Mike Blatt (Glasgow) is the lead on this UK-Sino-Australino-Argentine collaboration that investigates the role of nitrate reductase enzyme in potassium flux in guard cells. This flux is necessary for a plants adaption to the environment and is controlled by the activity of ABA via the activity of H2O2 and Nitric Oxide (NO). The authors showed that multiple responses to ABA were impaired in nia1nia2 nitrate reductase mutants, which includes the K+ IN current in guard cells, required for stomatal closure. This response was rescued by exogenous NO and allowed the authors to demonstrate that there exists a complex interaction involving ABA, NO, potassium nutrition and nitrogen metabolism that is necessary to ensure correct stomatal responses.

Kriechbaumer V, Botchway SW, Slade SE, Knox K, Frigerio L, Oparka K, Hawes C (2015) Reticulomics: Protein-Protein Interaction Studies with Two Plasmodesmata-Localized Reticulon Family Proteins Identify Binding Partners Enriched at Plasmodesmata, Endoplasmic Reticulum, and the Plasma Membrane Plant Physiol. 169(3):1933-45

This proteomic analysis of endoplasmic reticulum components is a collaboration between the Central Laser Facility at Didcot, Warwick, Edinburgh and Oxford Brookes Universities, led by Professor Chris Hawes. Plant Reticulon proteins (RTNLB) specifically populate and tubulate the ER, mediated by their varied multi-meric interactions. In addition, certain RTNLB are also present in plasmodesmata (PD) and two of these proteins, RTNLB3 and RTNLB6 were GFP-tagged, Co-IPed and interacting proteins were analysed by MS. This identified a range of known PD-localised proteins, and these interactions were experimentally verified in tobacco cells using FRET-microscopy. The authors suggest that this data shows that RTNLB proteins may play important roles in linking the cortical ER to the plasma membrane. This paper is the ‘sister’ to another manuscript in Plant Physiology that was highlighted in a recent Arabidopsis Research Roundup.