Unveiling Microbial Gene Functions in Maize Cultivars With Varying Drought Resistance.

Abstract

The rhizosphere microbiome is recognized as a "biological tool" for mitigating drought stress on plant development. However, the functional genes involved in plant-microbe interactions, particularly in drought-sensitive and drought-tolerant cultivars, remain poorly understood. This study comparatively evaluated the functional gene set of the maize rhizosphere microbiome in Monsanto DKC 72-70 (drought-tolerant) and CRN-3505 (drought-sensitive) maize genotypes at water holding capacity (WHC) values of 60, 80, and 100% via shotgun metagenomics. The findings revealed that both cultivars contained a variety of microbial taxa, such as Actinobacteria, Alphaproteobacteria, Gammaproteobacteria, and Bacilli, with plant stress tolerance genes. The analysis of beta diversity indicated significant differences between drought-stressed (60% WHC) and well-watered (100% WHC) conditions in both cultivars (R ≈ 0.57, 0.58; p < 0.01), which implies that the functional gene composition is different and that there are intermediate patterns at 80% WHC. In terms of functional responses, drought-sensitive maize presented increased expression of genes related to sulfur oxidation (soxA, soxB, soxD) and osmoprotectant synthesis (BetI, betC, CHCH), indicating a reactive stress response. Conversely, drought- tolerant maize presented regulated expression of the nitrogen metabolism (glnA) and iron homeostasis (FUR) genes in all the WHCs, thus indicating efficient adaptation. In addition, the drought-tolerant maize cultivar selectively expressed stress-response genes (SigB, AhpC) and protein protection genes (dnaJ, dnaK), whereas the drought-sensitive maize cultivar constitutively expressed these genes across conditions. This study provides novel evidence of cultivar-specific functional microbial signatures and demonstrates how microbial gene functions underpin drought tolerance in maize under varying water availability conditions.

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