| Summary: | Development of viable pollen in the anther locule is crucial for plant reproduction, and relies upon secretion of proteins, lipids, polysaccharides and other essential molecules from the surrounding tapetum tissue. Tapetum development in Arabidopsis thaliana is regulated by a number of genes including the basic Helix Loop Helix (bHLH) transcription factors DYSFUNCTIONAL TAPETUM (DYT1) and ABORTED MICROSPORES (AMS), which interact competitively with bHLH010, bHLH089 and bHLH091 to regulate downstream targets involved in synthesis and secretion of pollen wall components. Disruption of genes within the tapetum development pathway leads to male sterility and previous research has shown that ams, dyt1 and bhlh089 bhlh010 amiR-bHLH091 knockout mutants are completely male sterile, whereas the single and double bhlh010, -089 and -091 mutants are mostly fertile due to a high level of functional redundancy.
In this thesis bhlh089 bhlh091 and bhlh089 bhlh010 double mutants are revealed to show light-sensitive sterility, alongside recent observations of thermosensitive male sterility. In low light conditions, both bhlh double mutants exhibit severe pollen wall defects; however, whereas the bhlh89,10 double mutant shows later recovery of fertility, bhlh89,91 remains sterile throughout development suggesting that bHLH89, -91 and -10 have distinct functions in maintaining fertility in response to environmental stress.
RNASeq analysis of wild type and bhlh89,91 mutant light response highlighted differential regulation of genes related to sexual reproduction and hormonal responses. As transient assays demonstrated that bHLH89, 91 and -10 interact with DELLA proteins and MYB33/65, and bHLH-AMS heterodimers were found to more strongly induce target gene expression, it’s proposed that DELLA-dependent sequestration of bHLHs in different light environments regulates formation of AMS-bHLH dimers that activate genes involved in pollen development. bHLH89, -91 and -10 are further shown to undergo post-translational modifications leading to a new hypothesis on their role in regulating reproductive development in adverse conditions.
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