Bilateral BBSRC-FAPESP: Cellular and regulatory basis for early plant organ growth

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A central problem in Biology is to understand how genes cause organs to grow to a specific shape and size. Plants are convenient to address this question because their overall growth results primarily from the increase in cell numbers and increase in the size of individual cells (cell movement and "pruning" by cell death do not need to be considered). In addition, understanding organ growth in plants offers a clear path to practical use through the rational manipulation of crop growth and yield. A major bottleneck for understanding plant growth, however, is that although we know several genes that control the overall size and shape of organs, we do not understand what processes these genes control within cells (such as cell division or increase in cell mass) to result in a net effect on the total size and shape of organs. We aim to answer this question, by studying the early stages of floral organ development in the model species, Arabidopsis. Unprecedented opportunities to address the question above arise from two recent developments. One is the establishment of methods that allow quantitative, 3D analysis of cell geometry and cell division in growing organs. Using these methods, the UK partner in this project has recently found that a key regulator of organ growth, called JAGGED (JAG), has an unanticipated role in co-ordinating cell volume with cell division in developing organs. The second is the development of techniques for detection of all genes controlled by a given regulatory gene, at well-defined stages of organ formation - this can reveal the repertoire of cellular functions that are controlled by a regulatory gene. Our Brazilian/Dutch partners have been developing these methods and applying them to understand the role of genes that control floral organ development. Taking advantage of the complementary expertise, resources and biological interest of the UK and Brazilian/Dutch partners, we will extend both approaches to a key set of genes that control plant organ growth: JAGGED (JAG), AINTEGUMENTA (ANT) and CIN-TCP genes. We will test whether the co-ordination between cell size and cell division is a key feature of targeted by these genes at the early stages of organ growth. We will also test whether these genes target specific steps in cell division and clarify how the activities of these regulatory genes are combined during organ growth. Finally, we will identify the sets of genes controlled by JAG and CIN-TCP genes in the early stages of organ development - this will show to what extent the function of these genes overlap, and reveal the key cellular functions targeted by these genes to determine how the organs grow. One of the current priorities in developmental biology is to develop computer models that can simulate and predict the way organs and organisms grow. Addressing the questions in this proposal will be essential for connecting these models with molecular mechanisms that can be controlled experimentally. Ultimately, this knowledge will allow rational modification of plant organ growth, which has an obvious impact on crop performance. In addition to addressing a fundamental biological question with strategic relevance, our work will establish new and mutually beneficial long-term scientific links between UK and Brazilian institutions.