Overexpression of Transcription Factor WRKY76 in Rice Leaves Leads to Increased Photosynthesis and Plant Yield

The rate of leaf starch biosynthesis impacts overall plant growth and yield. Overexpression of ADP-glucose pyrophosphorylase (AGPase), the rate limiting enzyme in the starch pathway, has led to increased plant growth in multiple species. Our goal here was to identify and test transcription factors that themselves upregulate starch biosynthetic genes. To accomplish this objective, we examined rice genes upregulated in response to overexpression of leaf AGPase, and identified the transcription factor (TF) WRKY76 as a potential regulator of the rice leaf starch biosynthesis pathway. Overexpression of WRKY76 in rice (Oyrza sativa) leaves led to a 27% increase in plant growth and seed yield. The enhanced productivity phenotype in rice overexpressing WRKY76 was associated with a 40% increase in leaf starch levels at one month after planting and at anthesis. This was accompanied by a 16% increase in photosynthetic rate and 20% increase in net carbon metabolism, indicating that WRKY76 positively regulates leaf starch biosynthesis and carbon metabolism. Interestingly, increased expression of WRKY76 led to changes in expression of other WRKY TFs, indicating that the mechanism by which WRKY76 regulates starch biosynthesis involves a complicated regulatory network. This research indicates that WRKY76 directly increases expression of genes involved in leaf starch biosynthesis