Impact of abiotic stress on plant reproduction and seed set

This project will explore the impact of stress on pollen development focusing on the role of gibberellin (GA) on fertility under adverse conditions. Pollen development involves a series of complex interactions between maternal tissues in the anther and the developing gametophytic tissues (pollen). A key maternal tissue in the anther is the tapetum, this cell layer is critical to the regulation of pollen development and pollen wall formation, with defects in the tapetum resulting in pollen degeneration and sterility. The tapetum goes through a regulated programmed cell death process and the timing and progression of this is critical for functional pollen development. Abiotic stress, in particular temperature stress, causes significant abnormalities to the tapetum and resulting sterility. It is known that bioactive GAs control microsporogenesis through their targeted degradation of the growth repressing DELLA proteins. Studies in rice have demonstrated the importance of GAs acting in the tapetum to control secretion of wall materials for the developing microspores and also promote tapetal breakdown. We have identified many of the key transcriptional regulators of tapetum development and the regulatory pathways that they are involved in. We have preliminary data that some of these factors act by binding DELLA proteins involved in the regulation of gibberellin responses. In a joint project between Rothamsted and Nottingham, we have identified two closely related bHLH transcription factors (TFs) in Arabidopsis, expressed exclusively in the tapetum and developing microspores, which interact with DELLA proteins. Our preliminary genetic evidence supports a role for these novel bHLH TFs in controlling GA-responsive anther development. We are currently testing our hypothesis that DELLAs block anther development through their sequestration of these bHLH TFs. This project will explore these interactions and determine their impact under abiotic stress. The project will also involve assessment of the impact of salt stress on fertility and a characterisation of whether this is occurring by similar changes as seen under heat stress. The project will involve molecular analysis of the interactions between these proteins, their expression patterns and impact on pollen development. It will include use of confocal microscopy to confirm phenotypes, interactions and determine localisation of transcripts and proteins under normal and stress conditions. The work will be principally be conducted in Arabidopsis and barley, however the project will benefit from associated collaborative work at Rothamsted Research on wheat GA reproduction pathways. The long-term aim of the project is to develop mechanisms to overcome the impact of abiotic stress during plant reproduction and thus maintain crop yields in adverse conditions.