Researchers identified a maize mutant, ven2, with impaired sucrose metabolism, leading to changes in protein accumulation. The study highlights the role of the transcription factor SRF1 in translating sugar signals into increased production of α-zein proteins, offering new insights into seed development and potential breeding strategies to improve grain quality.
Maize seeds store energy and nutrients in the form of starch and proteins, with α-zeins making up over 60% of total protein. These proteins contribute significantly to seed structure, nutritional value, and resistance to mechanical damage. While transcription factors like OPAQUE2 and PBF1 have been identified as central regulators of zein gene expression, the upstream signaling mechanisms controlling their activity remain poorly understood. Sucrose not only fuels seed development but also acts as a signal that can influence gene expression, particularly in the developing endosperm where nutrient allocation is critical. Until now, the link between sucrose metabolism and zein protein synthesis remained largely speculative.
A study (DOI: 10.48130/seedbio-0025-0008) published in Seed Biology on 24 June 2025 by Xiangyu Zhao’s team, Shandong Agricultural University, elucidates a sucrose–SRF1–α-zein regulatory axis, providing mechanistic insight into how sugar signaling orchestrates protein biosynthesis during maize seed development.
To dissect the molecular relationship between sucrose metabolism and seed storage protein synthesis in maize, researchers employed a combination of genetic, molecular, biochemical, and transcriptomic analyses. They began by identifying a mutant, vitreous endosperm 2 (ven2), from an EMS-mutagenized B73 population. Genetic mapping using F₂ segregating populations narrowed the mutation to Zm00001d003776, encoding the enzyme cell wall invertase II (INCW2). Sequencing confirmed a G-to-A substitution in this gene. Complementary allelism tests with two additional ven2 alleles (ven2-1 and ven2-2) validated INCW2 as the causal gene. Phenotypically, ven2 seeds were significantly smaller, showed a vitreous and hardened endosperm, had reduced starch content, and accumulated elevated levels of 19 kDa and 22 kDa α-zeins, without changes in non-zein proteins. High-resolution SEM revealed densely packed small starch granules in ven2, embedded in a protein matrix. Biochemical assays further confirmed that ven2 mutants had increased sucrose and reduced glucose/fructose in the basal endosperm, a hallmark of impaired invertase activity. To determine whether sucrose acts as a signaling molecule influencing zein gene expression, promoter analysis identified W-box sugar-responsive elements in the α-zein promoters. Endosperm cultured in sucrose-rich media showed increased α-zein expression, and luciferase assays confirmed promoter activation by sucrose. In contrast, overexpression of INCW2 under a zein promoter (OE-Incw2) led to decreased sucrose and zein accumulation. RNA-seq revealed that ven2 mutants upregulated storage protein biosynthesis genes and downregulated starch biosynthetic genes, consistent with observed phenotypes. Among sugar-responsive transcription factors, SRF1, a WRKY protein, was significantly induced by sucrose and shown to directly bind α-zein promoters via W-box elements, as confirmed by dual-luciferase and EMSA assays.
These findings suggest a direct regulatory pathway in which sucrose levels modulate storage protein accumulation via the sugar-responsive transcription factor SRF1. By manipulating sucrose signaling or SRF1 activity, breeders could optimize the protein content and quality of maize kernels. This has significant implications for improving seed texture, nutrient density, and overall crop value, particularly in varieties used for human consumption and animal feed.
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References
DOI
10.48130/seedbio-0025-0008
Original Source URL
https://doi.org/10.48130/seedbio-0025-0008
Funding information
This work was supported by the National Natural Science Foundation of China (32071921), the Natural Science Foundation of Shandong (ZR2023QC162 and ZR2024QC152), Shandong Provincial University Youth Innovation and Technology Program, China (2023KJ284), and the Taishan Scholars Project.
About Seed Biology
Seed Biology (e-ISSN 2834-5495) is published by Maximum Academic Press in partnership with Yazhou Bay Seed Laboratory. Seed Biology is an open access, online-only journal focusing on research related to all aspects of the biology of seeds, including but not limited to: evolution of seeds; developmental processes including sporogenesis and gametogenesis, pollination and fertilization; apomixis and artificial seed technologies; regulation and manipulation of seed yield; nutrition and health-related quality of the endosperm, cotyledons, and the seed coat; seed dormancy and germination; seed interactions with the biotic and abiotic environment; and roles of seeds in fruit development. Seed Biology publishes a wide range of research approaches, such as omics, genetics, biotechnology, genome editing, cellular and molecular biology, physiology, and environmental biology. Seed Biology publishes high-quality original research, reviews, perspectives, and opinions in open access mode, promoting fast submission, review, and dissemination freely to the global research community.