Using Brachypodium as a Model to Study Key Genes Regulating Reproductive Development in Temperate Grasses

MADS-box genes encode a family of transcription factors (TFs) that are central to reproductive development in plants. Within this family, C-class and D-class genes control the development of the third and the fourth whorls in flowers that contain the reproductive organs, stamens and carpel, respectively. Investigating the role of these genes in essential crops such as wheat and barley will provide new insights into the genetic and molecular control of the formation of floral organs and in grain development. This study aimed to investigate the roles of C and D class genes in the monocot grass model system, Brachypodium in comparison to wheat and barley. The first objective was to identify all MADS-box MIKC-type genes in four species (Brachypodium distachyon, Oryza sativa, Triticum aestivum, Hordeum vulgare and Arabidopsis thaliana) and investigate their spatio-temporal expression patterns across developmental stages to suggest potential functions. The second objective was to investigate the effect of the loss-of-function of BdMADS3 from C-lineage, and BdMADS13 from the D-lineage on Brachypodium distachyon and try to select their potential targets.

This study established that there was an expansion in some MADS-box genes families in wheat and barley. Also, these genes were expressed during grain development which may suggest roles here. The comparative quantitative expression of C and D-class genes showed a conserved pattern across the three species (Brachypodium, wheat and barley) in addition to their high expression during grain filling. This expression was localised in Brachypodium grain sections in the degenerating mesocarp prior and after anthesis, then in the cellularising syncytial endosperm at full length stage, and finally in the aleurone layer at maturity. Furthermore, our functional analysis of BdMADS3 and BdMADS13 in Brachypodium revealed they are essential for plant fertility and proper spikelet formation. Finally, differential expression showed that BdMADS13 might regulate the reactive oxygen species level at pre-anthesis stage.