Identification of candidate genes and proteins for tasseling stage drought tolerance through integrated transcriptomic and proteomic analysis approach in maize

Drought stress, particularly at the tasseling stage, is the most devastating abiotic factor and major contributor to yield reduction in maize (Zea mays L.). Despite recent scientific advances in deciphering maize drought stress responses, the overall picture of key genes and proteins regulating maize tasseling drought tolerance remains less understood. In this study, we conducted comparative physiological, transcriptomic and proteomic analyses to monitor the changes in the leaf tissues of two contrasting maize hybrid cultivars exposed to drought stress at the tasseling stage. We identified 1701 differentially expressed genes (DEGs) in RNA-sequence runs and 424 differentially expressed proteins (DEPs) from an iTRAQ-based analysis. Mapman analysis revealed several regulatory processes influenced by drought conditions, including signal transduction, cell-wall remodeling, cellular redox homeostasis and hormone metabolism that were observed at both mRNA and protein levels. However, transcription factor regulation and secondary metabolism were specifically identified at the transcript level, whereas photosynthesis was uniquely identified to be affected by drought stress at the protein level. Meanwhile, a weak correlation between DEGs and DEPs was observed, indicating the drought response of maize at tasseling stage is largely regulated post-transcriptionally. Furthermore, comparative physiological analysis and qRT-PCR results substantiated the trancriptomic and proteomic findings. Additionally, we screened ZmPOD, ZmRAV1, ZmTPP and performed phenotypical and physiological characterizations of transgenic Arabidopsis thaliana (Arabidopsis) lines and wild-type. Resultantly, the transgenic Arabidopsis lines exhibited stronger tolerance to drought than the WT. This functional verification reinforces the reliability of our omics-based candidate gene selection. Overall, our research provides insights on the drought-responsive genes and pathways mediating maize drought tolerance at the tasseling stage.