Abstract
Maize is one of the three major crops worldwide based on its yield and quality. Starch is crucial to both the yield and quality of maize as it accounts more than 60% of the seed weight, and its structure influences the quality of the crop. Starch synthase I (SSI) contributes to the majority of the starch synthase activity in the maize endosperm. An in-depth understanding of the starch synthesis regulatory mechanism would provide opportunities for improving the yield and quality of maize. In this study, ZmPLATZ2, a plant AT-rich sequence and zinc-binding protein (PLATZ) transcription factor related to starch synthesis, was selected based on co-expression analysis. The semiquantitative RT-PCR and qRT-PCR assays revealed that ZmPLATZ2 had a high expression in the endosperm, and reached the peak at 12 days after pollination (DAP). Different treatments demonstrated that ZmPLATZ2 was downregulated by the presence of sucrose. Subsequent transactivation and subcellular localization analyses showed that ZmPLATZ2 was localized in the nuclei without transactivation. Yeast one-hybrid and transient expression in maize endosperm indicated that ZmPLATZ2 could bind to the promoters of ZmSSI, ZmISA1, and ZmISA2 and increase their gene expression. After ZmPLATZ2 overexpression in rice, four starch synthesis genes were significantly upregulated in the transgenic plant, including the OsSSI gene. In vitro DAP-seq data showed that ZmPLATZ2 could bind to the CAAAAAAA element. In conclusion, our data support that ZmPLATZ2 binds to the CAAAAAAA element in the ZmSSI promoter and mediates the Glu signal pathway.
Highlights
Maize (Zea mays) is an important crop that contributes to solving the food security problem (Godfray et al 2010)
PLATZ1 is the first reported member of the PLATZ Transcription factors (TFs) family, which was identified from the pea (Pisum sativum) (Nagano et al 2001)
The first reported member in maize was ZmPLATZ12(fl3), which was expressed in Semiquantitative RT-PCR showed that ZmPLATZ2 was mainly expressed in the endosperm and further series experiments showed that ZmPLATZ2 harbored the PLATZ domain and was located in the nucleus
Summary
Maize (Zea mays) is an important crop that contributes to solving the food security problem (Godfray et al 2010). Starch accounts for more than half the weight of the seed; increasing the starch content is an essential measure for improving the yield. Four types of enzymes are involved in the starch biosynthesis reaction: adenosine diphosphate glucose pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE), and starch debranching enzyme (DBE) (Leterrier et al 2008; Zhou et al 2016; Hennen-Bierwagen et al 2008). IbSSI, a soluble starch synthase I gene, is involved in the synthesis of amylopectin chains and alters the content and structure of starch in the sweet potato (Wang et al 2017). DBE is responsible for generated linear starch fraction (Reddy et al 2018). These four enzymes, during the seed filling period, influence the starch content and accumulation rate
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