A maize NAC transcription factor, ZmNAC34, negatively regulates starch synthesis in rice.

KEY MESSAGE: ZmNAC34 might function as an important regulator of starch synthesis by decreasing total starch accumulation and soluble sugar content and increasing amylose fractions. Starch is a major component in endosperm and directly influences seed yield and the cooking quality of cereal grains. Starch is synthesized through a series of complex biological processes. Nevertheless, the mechanism by which starch biosynthesis is regulated in maize is still unclear. In this study, ZmNAC34, a NAC transcription factor related to starch synthesis, was screened based on transcriptome sequencing data. Subsequent qRT-PCR analysis showed that ZmNAC34 is specifically expressed in maize endosperm. Transactivation and subcellular localization assays revealed that ZmNAC34 possesses two characteristics of transcription factors: nuclear localization and transactivation activity. Overexpression of ZmNAC34 in rice decreased total starch accumulation and soluble sugar content, while increased amylose fractions. Meanwhile, the transgenic seeds exhibited alterant starch structure and abnormal morphology. In addition, compared with WT seeds, most of the 17 starch biosynthesis-related genes were significantly upregulated in transgenic seeds from 6 to 15 DAP (day after pollination). These data reveal that ZmNAC34 might function as an important regulator of starch synthesis, thus providing a new perspective on controlling seed yield and quality.