Theses and Dissertations Collection

The fine-turned regulation of plant hormones is essential for plant development and responses to the environmental stimulates because changes in trace concentration of hormones can influence diverse plant physiological processes. Thus, it is extremely important for plants to precisely control the balance between biosynthesis and catabolism of hormones. Although the biosynthesis pathways of plant hormones have been clearly established, the regulatory mechanisms of them are still vague. In this study, we find that the tomato genes SlSINA3 and SlWOX14 control plant vegetative growth and regulate the SlGA3ox1 responsible for biosynthesis of bio-active gibberellic acids (GAs). How SlSINA3 and SlWOX14 interact, and how they regulate the GA biosynthesis at molecular levels will be introduced. Previously, we have shown that the tomato ubiquitin ligase SlSINA3 plays a negative role in plant defense. However, little is known about its function in plant development and growth. Transgenic tomato plants overexpressing SlSINA3 (SlSINA3-OX) exhibit significant dwarf phenotype. The qRT-PCR analysis revealed that two GA-related anabolism and catabolism genes, SlGA3ox and SlGA2ox, are down-regulated and up-regulated in SlSINA3-OX plants, respectively. This result indicates that overexpression of SlSINA3 may suppress plant growth via indirectly suppressing GA biosynthesis, thereby resulting in a typical GA-defective dwarfism. In addition, changes in chlorophyll content and pollen activity in SlSINA3-OX transgenic plants were also consistent with the phenotypes of GA deficient plants. In line with this notion, we also found SlSINA3 can interact with and promote the degradation of SlWOX14, a transcription factor that regulates the expression of SlGA3ox1 by directly binding to its promoter. The SlWOX14-KO mutant plants generated by CRISPR/Cas9 exhibited similar GA-defective phenotypes as SlSINA3-OX transgenic plants did. Thus, we hypothesize that SlSINA3-SlWOX14 function as regulatory module controlling plant growth by manipulating genes (such as SlGA3ox1) involved in GA biosynthesis, in which, SlSINA3 promotes the degradation of SlWOX14 transcription factor presumably via ubiquitination.