Genetic and transcriptomic identification of WPG1 controlling nitrogen allocation-related leaf chlorisis and premature senescence in wheat

Leaf senescence is a turning point for grain development, closely related to yield and grain quality. Fine-tuning leaf senescence could be a vital strategy for yield improvement. However, our knowledge of the regulatory genes of leaf senescence is limited in wheat. In this study, we identified a methanesulfonate (EMS) mutant, wheat pale green 1 (wpg1), exhibiting obvious leaf chlorisis and premature senescence (PS) since the jointing stage. The chloroplast structure of the chlorisis leaf of wpg1 seemed intact, whereas its chlorophyll content was significantly decreased compared to the wild type (WT). The content of nitrogen (N), the core element for chlorophyll, was much lower in leaves of wpg1 than in WT. The spatio-temporal pattern analysis of nitrogen content further indicated accelerated N allocation from vegetation tissues to spike in wpg1, resulting in a significant decrease in nitrogen content in leaves, but a substantial increase in grains compared to WT. Genetic analysis showed that leaf chlorisis and PS is controlled by a single dominant locus, designated as Wheat Pale Green 1 (WPG1), which was further mapped to a physical interval of 34.69M-41.19M on chromosome 2A. Transcriptomic analysis revealed that expression of photosynthesis-related genes, N absorption and transportation genes consistently decreased in wpg1, which revalidated the underlying relationship between N shortage and leaf chlorisis. The results presented here lays the basis for further dissecting the causal gene of WPG1 and the subsequent molecular mechanism underlying the regulation of leaf senescence, N allocation, and possibly photosynthesis in wheat.