Date of Award
Doctor of Philosophy
Genetics, Development and Cell Biology
Brassinosteroids (BRs) are the steroids hormone widely found in many plant species, which play important roles in many aspects of plant life, including cell elongation, leaf development, root growth, abiotic and biotic stress responses, reproduction and fruit development. Studying BR signaling pathway not only provides mechanisms of plant development and stress responses, but also shed light on agricultural application of BRs to improve yield and stress resistance.
This dissertation firstly discussed the general knowledge of BRs, including the diversity and biosynthesis, physiological function, signaling pathway of perception, transduction, transcriptional regulation, interaction with stress signaling, and applications.
Then a study of interaction between BRs signaling and drought stress pathway was included. Drought is one of the major challenges for agriculture and will become more challenging in the future because of climate changes. Previous study revealed that a dehydration induced transcription factor, RESPONSIVE TO DESSICATION 26 (RD26), physically interacts with BR signaling transcription factor, BRI1-EMS-SUPPRESSOR 1 (BES1), to antagonize the growth and drought responses. BRASSINOSTEROID-INSENSITIVE 2 (BIN2), which is the kinase of BES1, was found to phosphorylate and stabilize RD26 to enhance the drought responses. Moreover, BIN2 can be dephosphorylated by ABA INSENSTIVE 1 (ABI1), which is an important phosphatase of Abscisic acid (ABA) signaling. This study establishes a link between drought-ABA and BR signaling pathways.
Lastly, a forward genetic screen for the suppressor of BR gain-of-function mutant bes1-D revealed that BES1 S-nitrosylation functions to modulate BR signaling. The mutation in S-NITROSOGLUTATHIONE REDUCTASE (GSNOR) increased the S-nitrosoglutathione (GSNO) level, causing increased S-nitrosylation of BES1 protein. Transcriptomic analysis showed that the BR regulated genes and BES1 regulated genes were mis-regulated when GSNOR was mutated. The S-nitrosylation of BES1 decreased the DNA binding affinity on target genes, which reduces BR signaling.
The dissertation applied both forward genetic and reverse genetic approaches, as well as molecular and biochemical tools to study the BR signaling in Arabidopsis. ABI1-BIN2-RD26 regulatory module established a new mechanism for balancing ABA regulated stress signaling and BR regulated growth signaling. bes1-D suppressor screening revealed that BES1 S-nitrosylation played a negative role in BR signaling by inhibiting BES1 DNA binding ability. Future research on the environmental signals that trigger the BES1 S-nitrosylation will help our understanding of coordination of plant growth and stress responses.
Jiang, Hao, "Forward and reverse genetic studies of Brassinosteroids signaling" (2020). Graduate Theses and Dissertations. 18153.
Available for download on Sunday, August 28, 2022