The novel ZmTCP7 transcription factor targets AGPase-encoding gene to regulate storage starch accumulation in maize.

The process of starch biosynthesis is a major developmental event that affects the final grain yield and quality in maize ( L.), and transcriptional regulation plays a key role in modulating the expression of the main players in the pathway. , which encodes the small subunits of AGPase, is a rate-controlling gene of the pathway; however, much remains unknown about its transcriptional regulation. Our earlier study identifies a short functional fragment of promoter (394-bp), and further shows it contains multiple putative -acting regulatory elements, demonstrating that several transcription factors may govern expression. Here, we identified a novel TCP transcription factor (TF), ZmTCP7, that interacted with the functional fragment of the promoter in a yeast one hybrid screening system. We further showed that ZmTCP7 is a non-autonomous TF targeted to the nucleus and predominantly expressed in maize endosperm. Using promoter deletion analyzes by transient expression in maize endosperm protoplasts combined with electrophoretic mobility shift assays, we found that ZmTCP7 bound to GAACCCCAC elements on the promoter to suppress its expression. Transgenic overexpression of in maize caused a significant repression of transcription by ~77.58%, resulting in a 21.51% decrease in AGPase activity and a 9.58% reduction in the endosperm starch content of transgenic maize. Moreover, the expressions of , , and were increased, while those of and reduced significantly in the endosperm of the transgenic maize. Overall, this study shows that ZmTCP7 functions as a transcriptional repressor of and a negative regulator of endosperm starch accumulation, providing new insights into the regulatory networks that govern expression and starch biosynthesis pathway in maize.