Integrated metabolome and transcriptome analysis of maize roots response to different degrees of drought stress

Plants in arid environments can regulate the generation of specialized metabolites to enhance their adaptability. Roots serve as the first defense line, responding directly to drought situations; however, the knowledge regarding the molecular mechanisms of metabolite changes to drought in maize roots remain largely limited. Here, we employed RNA-seq and UPLC-MS/MS methods to examine changes in the root metabolome and transcriptome of maize seedlings subjected to moderate drought (MD) and severe drought (SD) conditions by controlling water supply.

Compared to the untreated control group, 460 differentially accumulated metabolites were detected in roots under MD and SD conditions. Among these metabolites, lignin compounds emerged as the primary response to drought. Most lignin metabolites, including caffealdehyde, sinapyl alcohol, coniferaldehyde, p-coumaryl alcohol, and p-coumaric acid, showed a significant increase under MD but decreased under SD. Transcriptional profiling identified 903 and 5306 differential genes in roots treated with MD and SD, respectively. The majority of these genes were associated with lignin biosynthesis, hormone synthesis and signal transduction, and defense response processes. These metabolites and genes play crucial roles in lignin biosynthesis, antioxidant capacity, hormone balance, and root growth, particularly under MD conditions, which aligns with the results from morpho-physiological studies. Further, a conjoint omics analysis highlighted the significant regulatory roles of hormone-associated genes in lignin formation.

Our results suggest that the co-regulation of the lignin biosynthesis pathway and hormone signals significantly enhances root performance, helping maize maintain growth under MD conditions. This study leads to a better understanding of the regulatory mechanisms involved in maize root adaptation to drought environments.