AUTHOR=Ajayo Babatope Samuel , Li Yangping , Wang Yayun , Dai Chengdong , Gao Lei , Liu Hanmei , Yu Guowu , Zhang Junjie , Huang Yubi , Hu Yufeng 

TITLE=The novel ZmTCP7 transcription factor targets AGPase-encoding gene ZmBt2 to regulate storage starch accumulation in maize

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.943050

DOI=10.3389/fpls.2022.943050

ISSN=1664-462X

ABSTRACT=<p>The process of starch biosynthesis is a major developmental event that affects the final grain yield and quality in maize (<italic>Zea mays</italic> L.), and transcriptional regulation plays a key role in modulating the expression of the main players in the pathway. <italic>ZmBt2</italic>, 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 <italic>ZmBt2</italic> promoter (394-bp), and further shows it contains multiple putative <italic>cis</italic>-acting regulatory elements, demonstrating that several transcription factors may govern <italic>ZmBt2</italic> expression. Here, we identified a novel TCP transcription factor (TF), ZmTCP7, that interacted with the functional fragment of the <italic>ZmBt2</italic> 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 <italic>ZmBt2</italic> promoter to suppress its expression. Transgenic overexpression of <italic>ZmTCP7</italic> in maize caused a significant repression of <italic>ZmBt2</italic> 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 <italic>ZmBt1</italic>, <italic>ZmSSI</italic>, <italic>ZmSSIIa,</italic> and <italic>ZmSSIIIa</italic> were increased, while those of <italic>ZmSh2</italic> and <italic>ZmSSIV</italic> reduced significantly in the endosperm of the transgenic maize. Overall, this study shows that ZmTCP7 functions as a transcriptional repressor of <italic>ZmBt2</italic> and a negative regulator of endosperm starch accumulation, providing new insights into the regulatory networks that govern <italic>ZmBt2</italic> expression and starch biosynthesis pathway in maize.</p>