Regulatory Mechanisms of Free Umami Amino Acid Accumulation in Fresh Waxy Kernels: Insights from Transcriptome and Metabolomics Analyses

Free amino acids play a key role as flavor components and metabolic precursors in fresh corn, with umami taste largely attributing to their concentration, particularly the umami amino acid glutamate and aspartate. While several genes involved in the biosynthesis of these amino acids have been identified, their regulatory pathways remain poorly understood. Sweet waxy corn 'Qianjiangnuo No.3' (Q3) and waxy corn 'Huayunhuanuo 402' (H402), with contrasting umami taste, were used in this study. Transcriptomic, metabolomic, and targeted metabolite profiling were conducted at kernel-filling stage. Our analysis showed that Q3 ears possessed significantly higher levels of free amino acids than H402, and its umami amino acids were highly enriched. Diverse enrichment of amino acids was observed across the isolated kernels distribution in ears. The <i>O2</i> (<i>bZIP1</i>), <i>Naked endosperm1</i> (<i>NKD1</i>), and <i>bZIP</i> genes were found significantly downregulated in Q3 compared to H402. Conversely, genes involved in glutamate and aspartate biosynthesis showed higher expression in Q3 than H402 while translation-associated genes <i>snoRNA U3-2</i> and <i>rRNA28S</i> exhibited lower expression in Q3 than H402, correlating with a notable enrichment of free umami amino acids. Genes promoter analysis revealed an abundance of <i>bZIPs</i> binding motifs. These findings suggest that <i>bZIP</i> members may act as central regulators modulating free amino acid synthesis and accumulation in fresh kernels.