Top international scientific journal Cell published online a research paper by Professor Yan Jianbing's team from Huazhong Agricultural University (HZAU) titled "A Zea genus-specific micropeptide controls kernel dehydration in maize" on Nov 12. The paper charted the process of kernel dehydration.
The study identified a small peptide, microRPG1, which affects kernel dehydration and is a novel 31-amino acid peptide specific to maize and its close relatives. This peptide originates from a non-coding sequence and controls kernel dehydration by precisely regulating the expression of key genes in the ethylene signaling pathway.
The study revealed the molecular mechanism of kernel dehydration in maize for the first time, laying an important foundation for breeding maize varieties suitable for rapid dehydration and mechanical harvesting.
Maize is the crop with the largest planting area and highest total yield in China, but it has long been limited by the lack of varieties suitable for rapid dehydration, resulting in lower water content in mechanically harvested maize kernels, affecting production efficiency and planting costs. So far, few genes controlling the rate of kernel dehydration have been cloned, and the underlying mechanism remains unclear, which is the fundamental reason why it is difficult to breed maize varieties suitable for rapid dehydration and mechanical harvesting through genetic improvement.
The mechanism by which microRPG1 regulates seed dehydration [Photo/news.hzau.edu.cn]
The research team has been continuously working on this key industry issue and has established field identification techniques for kernel dehydration phenotypes. Through QTL mapping using this technique, four QTLs affecting kernel dehydration were identified. This study focused on one major-effect QTL, qKDR1, and successfully narrowed it down to 1417-bp, revealing a non-coding DNA sequence that does not encode any proteins or transcribe, with a transposon sequence of about 6.2 kb between the parental sequences. Knocking out the parental sequences significantly reduced the rate of kernel dehydration, regardless of the presence of the transposon.
Analysis indicated that qKDR1 may act as a suppressor, inhibiting the expression of a gene named RPG (qKDR1 REGULATED PEPTIDE GENE) located about 10 kb upstream.
Further research found that RPG is the target gene regulated by qKDR1, and two transcription factors, ZmMYBST1 and ZmMYBR43, can bind to qKDR1 and suppress the expression of RPG.
QTL-KDR1 is the locus controlling kernel dehydration. [Photo/news.hzau.edu.cn]
RPG has not been annotated in the maize genome and is a completely new gene. Through various techniques, the research team jointly demonstrated that RPG functions by encoding a 31-amino acid peptide, named microRPG1. Knocking out microRPG1 accelerates the dehydration rate, while over-expression significantly reduces the dehydration rate. Further research revealed that microRPG1 may affect dehydration by regulating the expression of key genes, ZmEIL1 and ZmEIL3, in the ethylene signaling pathway.
RPG is expressed in maize kernels 26 days after pollination, reaching its peak at 38 days when maize kernels are mostly filled, and regulating ethylene expression can promote rapid dehydration of kernels without affecting yield, achieving a balance between yield and dehydration. This discovery also provides a new direction for precise control of kernel dehydration in the future.
MicroRPG1 is not homologous to any known small peptides in other species and is unique to maize and its close relatives. Whether this unique small peptide functions in other species was explored by synthesizing the peptide and applying it exogenously to Arabidopsis, resulting in a significant delay in fruit maturation and a notable increase in seed moisture content. Over-expression of microRPG1 in Arabidopsis also significantly delayed fruit maturation. Arabidopsis roots can absorb the peptide and transport it to the aerial parts. These results suggest that microRPG1 may have a conserved function in other species, providing imaginative space for further exploration of the peptide's application value.
Maize kernels suitable for mechanized harvesting require a moisture content between 15% and 25%, but most maize varieties in China typically have a moisture content between 30% and 40% at harvest.
Experiments conducted over many years and locations showed that knocking out microRPG1 can reduce the moisture content of harvested kernels by 2% to 17%, with an average decrease of 7%, while other agronomic and yield traits show no significant changes. Analysis of hundreds of representative maize germplasm materials revealed that almost all materials contain the RPG gene, indicating that manipulating RPG to alter the rate of kernel dehydration for breeding varieties suitable for mechanical harvesting has enormous potential.
It is reported that the team has laid out multiple patents related to the precise control of maize kernel dehydration and has authorized Wimi Biotechnology Co Ltd to carry out commercial applications, with significant progress already achieved.
Professor Yan Jianbing, of the National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory and Yazhouwan National Laboratory, is the corresponding author of this paper. PhD students Yu Yanhui and Liu Yuanfang and Associate Professor Li Wenqiang are the joint first authors of this paper. Professors, faculty and students from Huazhong Agricultural University, Wimi Biotechnology Co Ltd, Huazhong University of Science and Technology, Yanzhouwan National Laboratory and the Max Planck Institute of Molecular Plant Physiology in Germany were involved in this work and provided valuable discussions.
This research was supported by the National Key R&D Program, the National Natural Science Foundation of China, the Department of Science and Technology of Hubei Province, and the 111 Project.
