Abstract
Drought stress causes heavy damages to crop growth and productivity under global climatic changes. Transcription factors have been extensively studied in many crops to play important roles in plant growth and defense. However, there is a scarcity of studies regarding WRKY transcription factors regulating drought responses in maize crops. Previously, ZmWRKY79 was identified as the regulator of maize phytoalexin biosynthesis with inducible expression under different elicitation. Here, we elucidated the function of ZmWRKY79 in drought stress through regulating ABA biosynthesis. The overexpression of ZmWRKY79 in Arabidopsis improved the survival rate under drought stress, which was accompanied by more lateral roots, lower stomatal aperture, and water loss. ROS scavenging was also boosted by ZmWRKY79 to result in less H2O2 and MDA accumulation and increased antioxidant enzyme activities. Further analysis detected more ABA production in ZmWRKY79 overexpression lines under drought stress, which was consistent with up-regulated ABA biosynthetic gene expression by RNA-seq analysis. ZmWRKY79 was observed to target ZmAAO3 genes in maize protoplast through acting on the specific W-boxes of the corresponding gene promoters. Virus-induced gene silencing of ZmWRKY79 in maize resulted in compromised drought tolerance with more H2O2 accumulation and weaker root system architecture. Together, this study substantiates the role of ZmWRKY79 in the drought-tolerance mechanism through regulating ABA biosynthesis, suggesting its broad functions not only as the regulator in phytoalexin biosynthesis against pathogen infection but also playing the positive role in abiotic stress response, which provides a WRKY candidate gene to improve drought tolerance for maize and other crop plants.
Highlights
Maize (Zea mays L.) is a major food and fodder crop that effectively contributes to the economic values of countries worldwide
We noticed that the expression of ZmWRKY79 was enhanced under salt and drought stresses simulated by PEG treatment, suggesting its possible involvement in abiotic stress responses [27]
We identified the positive role of ZmWRKY79 in drought stress response
Summary
Maize (Zea mays L.) is a major food and fodder crop that effectively contributes to the economic values of countries worldwide. Long-term waterless conditions always contest crops’ survival and shift crops from growth to defense strategies These survival attempts mostly reduce grain or biomass yield [2]. In order to cope with drought stress for sustainable maize productivity, several breeding programs are adopted, such as crop genetic engineering through the overexpression or mutation of drought-responsive genes for developing drought-tolerant transgenic crops [3,4]. In this respect, there is an urgent need to study the underlying mechanisms involving physiological responses and molecular pathways that mediate substantial stress responses
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