The Meristem in Context: a multilevel systems approach to improving plant growth under changeable environments

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Climate change is impacting the way plants grow, resulting in year on year reductions in the total consumable calories produced worldwide. Although plant productivity is often viewed at the organism level, yields are ultimately dependent on small groups of stem cells that are found in the growing tips of the plant's shoots and roots. The shoot apical meristem (SAM) produces all of the leaves, flowers, and stems that make up the plant's above-ground architecture. Its specialised domed structure is maintained through a well described system of mobile transcription factors and signalling molecules that balance cell growth and division against differentiation and organ initiation. Since new organs are initiated following a set of specific geometric rules, the size and cellular structure of the SAM are extremely important. For example, a large SAM comprised of many cells can accommodate a larger number of new organ primordia around the central stem cell pool than a smaller SAM, or a SAM comprise of fewer, larger cells. Indeed, many crop species have larger meristems than their wild relatives, a factor that is thought to contribute to their higher productivity. Despite the importance of SAM structure to plant yields, we know little about how the structure of the SAM is impacted and modulated by real-world environmental conditions. For example, are the larger SAMs of domesticated more or less sensitive to environmental stresses than the smaller SAMs of their wild relatives? And, can we improve robustness in crop yields by reducing environmental plasticity in SAM structure?One reason for our lack of understanding of how the SAM responds to stress is that the SAM is often studied in tissue culture, devoid of the context of the plant and its environment. This means that crucial information about how the SAM integrates environmental and developmental signals is lost. To address this problem I have devised an approach that will integrate cell biology with large scale phenotyping and multilevel modelling to start building a picture of the SAM within its normal physiological and environmental context. I will examine how well-defined cell growth, division and signalling pathways are modified during stress responses and what the effects these changes have on SAM structure and productivity. This will allow me to develop a framework through which we can reliably predict how the SAM will respond under to changeable, real-world conditions and identify genetic modifications that will improve its productivity. Importantly, this multilevel approach will allow me to use cell level modifications to make predictable changes to the overall architecture of the plant and bridge an existing gap between the wealth of fundamental knowledge collected at the cell level and the whole plant level at which we want to be able to make targeted modifications.My research will focus on drought as an important example plant stress response. Drought stress is a major cause of crop losses in the UK and worldwide and altered temperatures and rainfall patterns associated with climate change are exacerbating this problem. Hot, dry periods during spring are especially problematic for UK winter grain crops such as Oilseed Rape, which must undergo rapid shoot growth in spring to maximise seed yield. New crop varieties that are more tolerant of extreme and changeable weather conditions would therefore support UK agriculture and help feed the growing world population. I will therefore conduct my research using both a model species (Arabidopsis thaliana) and a crop species (Brassica napus - Winter Oilseed Rape) to ensure the generality of my findings. In the future I will be able to use the same approach to study other stresses such as the impact of heat and herbivory and identify whether there are common solutions to these related problems.