Transcriptomic and Metabolomic Profiling Reveal the Close Implication of Alkaloid Biosynthesis and Ureide Metabolism to Drought Stress Tolerance in Maize

Addressing sustainable agriculture production and food security requires a thorough understanding of the crop drought response. Although the importance of secondary metabolites in mediating drought tolerance (DT) has been extensively reported, the implication of alkaloids and urea in maize DT remains elusive. Here, through evaluating the physiological, transcriptome, and metabolome responses of two maize varieties, CIMMYT PAK (C, drought tolerant) and Haq Nawaz (H, drought sensitive), we found that alkaloid biosynthesis and ureide metabolism were particularly significantly induced under DS (drought stress) in C. Notably, lupanine and (S)-ureidoglycolate were 20.87-fold and over 37-fold up-regulated under DS in C. Five key candidate genes, including ZmAPY3, were uncovered. In addition, other critical pathways and genes in response to DS were revealed, highlighting key drought-responsive mechanisms in maize. Our results provide new insights into the DT mechanisms of maize. The molecular contribution of alkaloid and ureide metabolism to maize DT deserves further in-depth investigations.