Corn is commonly used as feed, and is also an important energy and industrial raw material. The endosperm accounts for about 90% of the dry weight of corn kernels, which largely determines the kernel weight and nutritional quality of corn kernels. Therefore, studying the regulation of endosperm filling is crucial for the genetic improvement of corn yield and quality. Ten days after corn pollination, the endosperm starts filling. The Sugar synthesized by leaf photosynthesis enters the endosperm through the basal transport layer at the base of the kernel, and the regulatory genes related to storage material synthesis are activated, and Starch and protein begin to be synthesized in large quantities. However, the molecular mechanism by which sugar promotes endosperm filling and storage material synthesis remains unknown.
Corn endosperm filling and storage substance Synthesis are regulated by a highly complex and precisely regulated genetic network. In 2023, the collaborative team of Yongrui Wu from the Chinese Academy of Sciences and Tao Yang from Sichuan Agricultural University published a review article entitled "Regulation of seed storage protein synthesis in monocot and dicot plants: A comparative review" in Molecular Plant, systematically summarizing and comparing the evolution, formation and regulatory networks of storage proteins in monocots and dicots, and proposing key scientific issues and genetic improvement strategies that need to be urgently addressed in storage protein research.
Opaque2 (O2) is a core regulatory factor in endosperm filling. Previously, the research team cracked the molecular mechanism of endosperm filling initiation regulation by analyzing the upstream regulatory network of O2. It was found that transcription factors ZmABI19 and ZmbZIP29 synergistically regulate multiple key proteins in endosperm filling, and clarified the phosphorylation mechanism of ABA signal regulation of maize endosperm filling initiation.
Recently, Yongrui Wu's team and Tao Yang's team published a research paper titled "Sucrose-associated SnRK1a1-mediated phosphorylation of Opaque2 modulates endosperm filling in maize" online in Molecular Plant, deeply analyzing the molecular mechanism of sugar signals promoting maize endosperm filling and storage material synthesis, constructing a regulatory module centered on Sucrose-SnRK1a1-O2, and proposing a new strategy for genetic improvement of high-yield and high-quality maize.
The study found that sugar promotes the expression of O2, a core regulatory factor in maize endosperm filling. The research team screened O2-interacting proteins through IP-MS and found that O2 interacted with SnKR1a1. Sugar, as a stimulatory signal, promotes O2 expression and storage material synthesis by inhibiting SnRK1a1 activity. SnRK1a1 has been shown to phosphorylate O2 at the 41st serine site and promote its protein degradation. This study analyzed the deep mechanism of low sugar inhibiting endosperm filling and storage material synthesis at the molecular level.
Fig. 1 SnRK1a1 phosphorylates O2 and regulates its transcriptional activity. (Yang, et al., 2024)
This study found that SnRK1a1 negatively and cooperatively regulates corn grain weight and starch and protein content. The grain weight, starch and protein content of snrk1a1 mutants were significantly increased, while SnRK1a1 Overexpression was the opposite. By constructing Transgenic materials with O2 overexpression, phosphorylation and dephosphorylation O2 variants, it was found that all three could increase corn grain weight. Dephosphorylated kernels became smaller, but the hard endosperm area, bulk density, starch and protein content increased. Phosphorylated kernels became larger, but the bulk density, starch and protein content did not change significantly. O2 overexpression kernels were a mixture of phosphorylated and dephosphorylated kernels, showing larger kernels, increased bulk density, starch and protein content. This study regulated the characteristics of O2 protein through Phosphorylation modification to achieve precise design for improving corn yield and nutritional quality.
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