Dissecting seed genetic networks through the evolution of plant life-cycle transitions

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The modern biosphere is dominated by plants that reproduce using seeds, which are critical to human agriculture and nutrition. Seeds are a relatively recent evolutionary innovation, arising in a single plant group (the seed-bearing plants) from an ancestral spore-based reproductive mechanism still present in living seedless plants (e.g. mosses, liverworts, ferns). How this dramatic change in plant development occurred is presently unknown and identifying genetic changes associated with it will substantially advance our fundamental understanding of how novel innovations in plant form can arise and improve our knowledge of the functions of economically-valuable genetic networks in modern seeds. This project aims to determine from where in seedless plant development seed genetic networks first arose. We will focus on a single candidate gene family; SPOROCYTLESS (SPL). SPL is a crucial regulator of seed development in flowering plants but is also found in species that do not make seeds. However, its function in seedless plant lineages is currently unknown. Mapping SPL expression and function before the evolution of seeds can therefore tell us about how plant seeds evolved.We will use a reverse genetics approach to compare the function and expression of the SPL gene family between the seed-bearing genetic model Arabidopsis thaliana, the model moss Physcomitrium patens (representing early diverging land plants) and the newly-established fern genetic model Ceratopteris richardii (belonging to the closest seedless relatives of the seed-bearing plants).. Analytical techniques will include functional knockout and ectopic expression of native homologs in seedless plants, , use of fluorescent reporters to map seedless gene expression and functional complementation between the three plant lineages.