Changing fates: rewiring gene expression in barley androgenesis

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In barley, it is possible to obtain plants derived from a single immature microspore, the type of cell that usually leads to the production of pollen grains. This is termed androgenesis, i.e. the process of obtaining a plant carrying only the genetic material (chromosomes) of the male parent. Indeed, microspores only carry a single copy of each barley chromosome, contrary to the pair normally carried in the barley plant. If this situation remains unchanged throughout the entire development of the plant derived from this microspore, it will result in these plants being sterile. Fortunately, a majority of the plants regenerated from immature microspores via androgenesis will undergo a spontaneous doubling of their chromosomes, thus restoring fertility. Such plants are termed "doubled haploid" and are highly valuable tools in both genetic analysis and breeding. Indeed, androgenesis is often used in plant breeding to expedite the development of new and improved varieties.******Although widely used, we have a rather limited understanding of how it is that a cell, normally destined to form a pollen grain, can undergo a complete shift in fate and start dividing in a highly organized fashion to produce an embryo and eventually a new plant. We hypothesize that this dramatic change in fate is due to a profound and rapid reprogramming of the genes that are expressed in the microspore. One can imagine that two types of processes need to occur: 1) the products of the genes needed to continue on the path towards pollen need to be destroyed (the slate has to be cleaned); and 2) new genes need to be expressed in order for the microspore to engage on the path to producing an embryo (a new set of instructions has to be given). We thus expect that major changes must occur to the list of expressed genes and their products found in the cell. We propose to investigate these changes (contrasting gene expression in both the path leading to pollen and the path leading to embryos) through a technique called RNA-Seq, a method that allow the extensive cataloguing of all the genes that are expressed in a cell.******To further explore how the necessary turnover occurs in the cell, we propose to investigate the population of small RNAs found in developing microspores. Such small RNAs have been shown to play important roles in development, both in plants and animals. Some specific types of small RNAs are known to target the destruction of some gene products. If this is the case when the microspore is undergoing its shift towards androgenesis, we expect to find small RNAs capable of directing the elimination of gene products normally needed to "build" a grain of pollen. Once a microspore has been thus deprogrammed, it can be reprogrammed to develop into an embryo by expressing a new suite of genes.******The results of this work will both enhance our basic knowledge of how plant cells can be reprogrammed and provide useful tools for optimizing androgenesis in barley.