Maize is the world's largest food crop, accounting for 41% of the world's total food production. Maize production plays an important role in promoting global food security and economic development. The compact corn plant size is conducive to increasing the planting density and thus increasing the corn yield. Leaf angle is a key trait that determines the compactness of maize plants, which directly affects the light energy utilization efficiency of maize populations. Cultivation studies have found that the application rate of nitrogen fertilizer in the field also affects the size of maize leaf angles, but the molecular mechanism is still unclear.
近日，中国农业科学院作物科学研究所李文学团队在The Crop Journal在线发表了题为“ZmbZIP27 regulates nitrogen-mediated leaf angle by modulating lignin deposition in maize”的研究论文，作者通过分析低氮处理下玉米叶枕部位的转录组数据，结合玉米维管束转录组公共数据库，挖掘到低氮胁迫下调控玉米叶夹角的关键基因ZmbZIP27，阐明了ZmbZIP27通过影响ZmmiR528的表达和叶枕部位的木质素沉积来调控氮素介导的叶夹角。
The researchers first dynamically measured the changes of leaf angle at seedling stage of maize under different concentrations of nitrogen supply, and found that the low nitrogen treatment significantly reduced the leaf angle of maize, and the change time of maize leaf angle under low nitrogen condition was earlier than the yellowing of leaves, indicating that the leaf angle of the inverted second leaf could be used as a morphological index to measure the response of maize to early low nitrogen stress (Fig. 1). The transcriptome data and resorcinol staining results of the leaf pillow of maize inverted bifolio under low nitrogen treatment showed that lignin deposition in the leaf pillow was involved in the nitrogen-mediated angle size of maize leaves. Combined with the maize vascular transcriptome public database, the ZmbZIP27 gene with high expression in the phloem of maize vascular bundle was preliminarily selected for further study. Low nitrogen stress induced the up-regulation of ZmbZIP27 gene expression. The results of in situ hybridization showed that ZmbZIP27 was highly expressed in the vascular phloem and vascular sheath of maize leaf occipital (Fig. 2). At the seedling stage of maize, overexpression of ZmbZIP27 gene could reduce the leaf angle and compensate for the effect of low nitrogen stress on the leaf angle of maize (Fig. 2). Compared with the wild type, the leaf angle of ZMBZIP27EMS mutant was significantly increased under normal nitrogen and low nitrogen treatments. Under field conditions, overexpression of ZmbZIP27 significantly increased the lignin content and the cell wall thickness of the distal axial pachyma in the occipital part of maize leaves, resulting in higher mechanical strength of the leaf midrib and thus reducing the leaf angle (Fig. 3). The researchers found that miR528 regulates the lignin synthesis of maize through the target genes ZmLAC3 and ZmLAC5, which in turn affects the lodging property of maize under high nitrogen conditions. The analysis showed that there was a binding site of ZmbZIP27 on the ZmMIR528a/b promoter, and EMSA and stem loop RT-qPCR experiments confirmed that ZmbZIP27 negatively regulated the expression of ZmmiR528 in maize leaf pillows. ZmmiR528 knockdown increased lignin content and decreased leaf angle in ear leaves, which was consistent with the leaf angle phenotype of ZmbZIP27 overexpressing plants (Fig. 4). In conclusion, this study constructed a molecular regulatory network of ZmbZIP27 to regulate the angle of maize leaves, elucidated the molecular mechanism of nitrogen supply on the development of maize leaf angle, and provided a new genetic resource for the cultivation of compact and dense maize.
Fig.1 Effect of nitrogen supply on leaf angle at maize seedling stage
Fig.2 Effect of nitrogen supply on leaf angle of ZmbZIP27 overexpressing plants
Fig.3 Overexpression of ZmbZIP27 increased the lignin content of maize leaf pillows
Fig.4 ZmmiR528 is involved in the molecular pathway of ZmbZIP27 regulating the angle of maize leaves
Authors and Funding Projects
Chen Huan, a doctoral student jointly trained by the Institute of Crop Science of the Chinese Academy of Agricultural Sciences and China Agricultural University, and Gong Xiaoping, a postdoctoral fellow who has been released, are the first authors of the paper, researcher Li Wenxue and associate researcher Du Qingguo are the co-corresponding authors, and Professor Yu Jingjuan of the College of Biology of China Agricultural University also participated in the related work. This research was supported by the National Science and Technology Major Project of Agricultural Biological Breeding (2023ZD04072), the Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences, and the Yazhou Bay Seed Laboratory of Hainan Province (B23YQ1507). The team is mainly engaged in the mining of lodging resistance gene resources and the analysis of the genetic mechanism of nutrient efficient utilization in maize.
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