Epigenetic control of the plant male gametophyte and germline

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Like animals, plants have a reproductive system which relies on the production of male and female reproductive cells - sperms and eggs - and a fertilization process. As almost all major crops require this sexual reproduction system to produce seeds, the importance of understanding the developmental biology of plant fertility and reproduction is critical. In animals, much recent work has shown that short information-carrying molecules of RNA ('small RNAs'/sRNAs) are essential for the development of male reproductive cells, a role which was never previously anticipated . The pathways in cells that generate and process these RNA molecules are consequently of great importance. In plants, there is now rapidly accumulating evidence to show that these RNA molecules have essential roles in regulating normal development and health of the plant, through controlling how genes are expressed, the way chromosomes are assembled and defence against parasites. Surprisingly, the role of sRNA pathways in regulating the reproduction of plants has not been studied - even though evidence is available to suggest that they are likely to fulfil the same kinds of important functions. For example, in the formation of the male reproductive cells (pollen) it is well established that there is a major change in the expression of many genes, a cycle of RNA abundance, and dramatic changes in the architecture of the chromosomes. Further, one biotechnology technique called RNAi (which relies on theses RNA pathways to work) has been shown to be effective in plant gametophytes. Our proposal will investigate - for the first time - the presence and function of these RNA processing pathways in the plant male gametophyte and germline (all contained in the pollen grain). Using a range of new technologies, we will use viral proteins that disrupt these pathways to determine the effect of perturbing their normal function on the development and fertility of the pollen. This will also allow us to find which genes in pollen may be regulated by small RNAs. We will investigate whether the genes that encode the various parts of the RNA processing pathways are active in the different cells that compose the pollen. Using a new sequencing strategy (454) we shall then attempt to sequence and identify all the sRNA molecules in the gametophyte, which will tell us immediately which genes are likely to be involved in this system. Finally we shall set up experiments to test whether a cellular system for processing a specific class of small RNA ('microRNA') is functional. In terms of benefits, this project will provide valuable information on how plants reproduce, allow meaningful comparisons to animal reproduction and generate new technology that will allow greater understanding of this economically important part of the plant life cycle.