ZmbZIP27 regulates nitrogen-mediated leaf angle by modulating lignin deposition in maize

In grain crops such as maize (Zea mays), leaf angle (LA) is a key agronomic trait affecting light interception and thus planting density and yield. Nitrogen (N) affects LA in plants, but we lack a good understanding of how N regulates LA. Here, we report that N deficiency enhanced lignin deposition in the ligular region of maize seedlings. In situ hybridization showed that the bZIP transcription factor gene ZmbZIP27 is mainly expressed in the phloem of maize vascular bundles. Under N-sufficient conditions, transgenic maize overexpressing ZmbZIP27 showed significantly smaller LA compared with wild type (WT). By contrast, mutant showed larger LA under both N-deficient and N-sufficient conditions compared with WT. Overexpression of ZmbZIP27 enhanced lignin deposition in the ligular region of maize in the field. We further demonstrated that ZmbZIP27 could directly bind the promoters of the microRNA genes ZmMIR528a and ZmMIR528b and negatively regulate the expression levels of ZmmiR528. ZmmiR528 knockdown transgenic maize displayed erect architecture in the field by increasing lignin content in the ligular region of maize. Taken together, these results indicate that ZmbZIP27 regulates N-mediated LA size by regulating the expression of ZmmiR528 and modulating lignin deposition in maize.