The final Research Roundup of 2016 includes two papers that take different strategies toward the ultimate aim of crop improvement and use Arabidopsis as a tool for their initial discoveries. Firstly Christine Raines (University of Essex) uses a transgenic approach to upregulate enzymes of the calvin cycle while researchers from Rothamstead and Oxford use a chemical intervention strategy. Both of these strategies are successful in increasing yield.
Second are a set of back-to-back papers featuring Xiaoqi Feng (JIC) that investigate DNA methylation patterns in both male and female gametes.
Finally Henrik Jonsson (SLCU) leads a paper that precisely defines the parameters that are important in determining the relationship between cell size, location and cytokinesis.
Simkin AJ, Lopez-Calcagno PE, Davey PA, Headland LR, Lawson T, Timm S, Bauwe H, Raines CA (2016) Simultaneous stimulation of the SBPase, FBP aldolase and the photorespiratory GDC-H protein increases CO2 assimilation, vegetative biomass and seed yield in Arabidopsis. Plant Biotechnol J http://dx.doi.org/10.1111/pbi.12676
GARNet Committee Member Christine Raines leads this UK-German study that alters the amounts of three calvin cycle enzymes and assesses the subsequent change in photosynthetic rate in Arabidopsis plants. These enzymes sedoheptulose 1,7-bisphosphatase (SBPase), fructose 1,6-bisphophate aldolase (FBPA) and the glycine decarboxylase H-protein (GDC-H) were overexpressed either individually or together and each plant shows an increase in the quantum efficiency of photosystem II. This results in improved CO2 fixation and a concomitant increase in leaf area and biomass. Overall the authors have shown that this transgenic gene stacking approach can have potential for improving plant productivity.
Griffiths CA, Sagar R, Geng Y, Primavesi LF, Patel MK, Passarelli MK, Gilmore IS, Steven RT, Bunch J,, Paul MJ, Davis BG (2016) Chemical intervention in plant sugar signalling increases yield and resilience. Nature
This study is a collaboration between Rothamstead Research and the University of Oxford and has been featured in a recent Nature podcast. This paper outlines a chemical intervention strategy to improve crop productivity and includes some fundamental work performed in Arabidopsis. They used a ”signaling-precursor concept” to design and synthesise a plant permeable version of Trehalose-6-phosphate (T6P), which could readily be uptaken and activated by sunlight in planta. Addition of T6P to wheat increases grain yield whilst when applied to leaf tissue it improves recovery from drought stress. This is an exciting test case to show the potential of chemical intervention yet the authors are rightly cautious when considering the general use of the compound given the variability of field conditions.
Hsieh PH, He S,, Buttress T, Gao H, Couchman M, Fischer RL, Zilberman D, Feng X (2016) Arabidopsis male sexual lineage exhibits more robust maintenance of CG methylation than somatic tissues. PNAS http://dx.doi.org/10.1073/pnas.1619074114
Xiaoqi Feng (John Innes Centre) is the corresponding author on this study that investigates the transgenerational maintenance of methylation through the male germline. They undertook the challenging purification of Arabidopsis pollen sperm and vegetative cells from both wildtype plants and plants that contains mutations within different DNA methytransferases. They show that background methylation is equivalent in sperm, vegetative and somatic cells but that specific CG methylation is higher in pollen sperm and vegetative cells than in somatic cells. The authors suggest that this allows more accurate inheritance of methylation patterns across successive generations.
Park K, Kim MY, Vickers M, Park JS, Hyun Y, Okamoto T, Zilberman D, Fischer RL, Feng X, Choi Y, Scholten S (2016) DNA demethylation is initiated in the central cells of Arabidopsis and rice. PNAS http://dx.doi.org/10.1073/pnas.1619047114
In this second of back-to-back papers, Xiaoqi Feng is a co-author on an international study that looks into the role of the DEMETER DNA demethylase on the control of gene expression in the endosperm. This tissue results from the fusion of a male pollen sperm cell and the female central cell and is associated with significant demethylation. This study documents the first genome-wide analysis of DNA methylation in the female central cell in Arabidopsis. They show that DNA demethylation requires DEMETER function but that it is likely not associated with the downregulation of the MET1 methytransferase. Therefore the authors suggest that characteristic endospermal DNA demethylation occurs through locus-specific activity.
Willis L,, Refahi Y, Wightman R, Landrein B, Teles J, Huang KC,, Meyerowitz EM,,, Jönsson H (2016) Cell size and growth regulation in the Arabidopsis thaliana apical stem cell niche. PNAS http://dx.doi.org/10.1073/pnas.1616768113
Henrik Jonsson (Sainsbury Lab Cambridge) is the corresponding author on this UK-US collaboration that uses a 4D imaging pipeline to track the growth of epidermal cells in the Arabidopsis shoot apical meristem (SAM). They suggest that neither cell size or cell age are determinants for progression to cytokinesis, which is also independent of cell contact topologies and the cell position within the SAM. However they find that a more complex mix of parameters determine the constraints on determination of cell size. Following cell division they also show that a smaller daughter cell will grow at a faster rather than its larger sister, a finding that the authors suggest challenges present models of growth regulation.