The Role of Brassinosteroids in the Ambient Temperature Floral Pathway of Arabidopsis thaliana

The current climate crisis has led to a rise in global temperatures, negatively impacting crop yields. Hence, there is an urgency to improve crops to enhance crop yields (Fitter & Fitter, 2002; McClung et al., 2016; Zhao et al., 2017). One trait directly linked to crop yield improvement is flowering time. Multiple environmental factors regulate flowering time, including photoperiod and temperature. Within the temperature pathways, ambient temperature is critical in regulating flowering. Low ambient temperatures repress flowering, while high ambient temperatures promote it (Blázquez et al., 2003). Central to this pathway is the MADS box transcription factor SVP. SVP represses flowering at low ambient temperatures by inhibiting the expression FT, a key floral inducer (Jeong et al., 2007). Noteworthy, the interaction with other temperature-responsive factors is crucial for SVP activity. Despite our current understanding of this pathway, the role of temperature-responsive hormones, including Brassinosteroids (BRs), in regulating the ambient temperature flowering pathway and SVP remains elusive. BRs are steroid phytohormones that play essential roles in ambient temperature-mediated growth at the seedling stage. Moreover, BRs regulate flowering time (Li et al., 2018). Whether BRs regulate ambient temperature flowering remains unknown. My MSc by Research aimed to understand the roles of BRs in the ambient temperature floral pathway in Arabidopsis. The results presented in this thesis indicate that BRs are involved in ambient temperature flowering through the interaction of SVP with the BR-responsive transcription factor BZR1. BZR1 acts as a flowering repressor through FT downregulation. Such repressive activity of BZR1 requires a functional SVP. Further research is necessary to understand the BZR1-SVP molecular relationship to expand our knowledge of how the BR and temperature crosstalk regulate the floral network.