Transcriptomic and physiological analyses of rice seedlings under different nitrogen supplies provide insight into the regulation involved in axillary bud outgrowth

BACKGROUND: N is an important macronutrient required for plant development and significantly influences axillary bud outgrowth, which affects tillering and grain yield of rice. However, how different N concentrations affect axillary bud growth at the molecular and transcriptional levels remains unclear. RESULTS: In this study, morphological changes in the axillary bud growth of rice seedlings under different N concentrations ranging from low to high levels were systematically observed. To investigate the expression of N-induced genes involved in axillary bud growth, we used RNA-seq technology to generate mRNA transcriptomic data from two tissue types, basal parts and axillary buds, of plants grown under six different N concentrations. In total, 10,221 and 12,180 DEGs induced by LN or HN supplies were identified in the basal parts and axillary buds, respectively, via comparisons to expression levels under NN level. Analysis of the coexpression modules from the DEGs of the basal parts and axillary buds revealed an abundance of related biological processes underlying the axillary bud growth of plants under N treatments. Among these processes, the activity of cell division and expansion was positively correlated with the growth rate of axillary buds of plants grown under different N supplies. Additionally, TFs and phytohormones were shown to play roles in determining the axillary bud growth of plants grown under different N concentrations. We have validated the functions of OsGS1;2 and OsGS2 through the rice transgenic plants with altered tiller numbers, illustrating the important valve of our transcriptomic data. CONCLUSION: These results indicate that different N concentrations affect the axillary bud growth rate, and our study show comprehensive expression profiles of genes that respond to different N concentrations, providing an important resource for future studies attempting to determine how axillary bud growth is controlled by different N supplies.