TgMYBS1-TgSUS1 regulatory module mediates sucrose metabolism in Torreya grandis kernels.

Sucrose synthase (SUS) is a key enzyme in sucrose metabolism, catalyzing the reversible synthesis and degradation of sucrose. It plays a crucial role in plant growth and development. Previous studies have shown that SUS-mediated sucrose metabolism is essential during various developmental stages in plants like Arabidopsis. However, its specific functions in Torreya grandis, an important economic tree species, have not yet been fully elucidated. Here, we identified five SUS genes in T. grandis and found that TgSUS1, a highly expressed gene in kernels, was significantly increased during kernels development. TgSUS1 protein was localized to the nucleus and cell membrane. Transient overexpressed TgSUS1 in kernels and heterologous overexpression of TgSUS1 in Oryza sativa significantly enhanced SUS activity in the sucrose cleavage (SS-c) direction and reduced sucrose content. Conversely, silencing TgSUS1 markedly reduced SS-c activity and increased sucrose content in kernels. Additionally, we found that the transcription factor TgMYBS1 directly bound to the promoter of TgSUS1 by Y1H and EMSA experiments. TgMYBS1 significantly reduced SS-c activity and increased sucrose content in kernels by inhibiting TgSUS1 expression. In summary, our findings indicate that TgMYBS1 directly inhibits the expression of TgSUS1 to suppress SS-c activity, thereby modulating the sucrose metabolism in T. grandis kernels.