Maize STARCH SYNTHESIS REGULATING PROTEINI positively regulates starch biosynthesis in rice endosperm

Starch is a major component of the endosperm, directly determining grain yield and quality. Although the key enzymes of starch synthesis have been identified and characterised, the regulatory mechanisms remain unclear. In this study, we identified the novel maize STARCH SYNTHESIS REGULATING PROTEIN1 (ZmSSRP1), which encodes a typical carbohydrate-binding module 48 (CBM48) protein. Expression analysis revealed that ZmSSRP I was highly expressed in the maize endosperm, while transient expression in maize leaf protoplasts showed localisation in the plastids, dependent on the N-terminal transit peptide. In addition, overexpression of ZmSSRPI in rice resulted in a decrease in grain thickness and the 1000-grain weight, as well as affecting the starch content and structure of the rice endosperm. The physicochemical properties of starch in the rice endosperm were also altered compared with the wild-type seeds. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was subsequently performed to determine the expression of starch synthesis-related genes, revealing upregulation of mRNA expression of most genes in the transgenic compared with wild-type lines. Collectively, these findings suggest that ZmSSRP I acts as a potential regulator of starch synthesis, providing new insight for molecular breeding of high-yielding high-quality maize.

Automated summary

This study identified a novel maize starch synthesis regulating protein, ZmSSRP1, and demonstrated its potential role in regulating starch synthesis. Overexpression of ZmSSRP1 in rice resulted in changes in grain quality and starch structure, providing insights for molecular breeding of high-yielding high-quality maize.