Coordinated Regulation of Carbon and Nitrogen Assimilation Confers Drought Tolerance in Maize (zea Mays L.)

Drought is a major limiting factor affecting crop productivity. To gain a comprehensive understanding of transcriptomic reprogramming under drought stress in maize (Zea mays L.), we performed physiological and transcriptomic analysis of leaf tissues of two maize cultivars, LY66 and LY99, subjected to a progressively severe drought and subsequent recovery. LY66 exhibited greater drought tolerance and recovery than LY99. RNA-Seq analysis showed that differentially expressed genes mainly enriched in pathways involved in carbon (C) and nitrogen (N) metabolism, and plant hormone signal transduction. As judged from RNA-Seq data, enzyme activity, and metabolite contents, LY66 maintained a higher relatively stable C and N metabolism than LY99, which were related to higher photosynthesis and sucrose biosynthesis capacity, higher N assimilation and protein biosynthesis capacity under drought stress, respectively. Interestingly, the expression of several genes encoding key enzymes involved in auxin biosynthesis and signaling were activated to higher levels in LY66 than in LY99 under drought stress. Our results indicate that LY66 exhibits coordinated regulation of C and N assimilation, possibly involved in phytohormone signaling pathways, which enhances drought stress tolerance.