Transcriptional analysis of maize elite inbred line Jing24 and the function of ZmMAPKKK21 in the response to drought stress

Drought, one of the most devastating abiotic stresses to affect agricultural production worldwide, causes significant crop yield loss. In China, the yield and value of maize, a drought-sensitive staple crop, is significantly affected by drought conditions. Jing24 (J24), an elite, robust, and drought-resistant maize inbred line, yet the underlying genetic basis for this resistance remains imperfectly understood. We characterized the overall performance of three maize varieties (J24, B73, and X178) under moderate and severe drought conditions at seedling and flowering stages. RNA-Seq analysis revealed more genes to respond to drought treatment in J24 than in either B73 or X178, with some drought-responsive genes were common to each line in leaf and root tissues. Gene ontology analysis of common differentially expressed genes in J24 and X178 showed ​that membrane and transporter-related genes were significantly enriched in roots, whereas genes associated with photosynthesis and membrane were most-enriched in leaves. The expression of ZmMAPKKK21 was significantly up-regulated in the root of J24 in the moderate drought treatment, the transgenic Arabidopsis plants overexpressing ZmMAPKKK21 we obtained exhibited a substantial reduction in ABA sensitivity and ​an increase in drought tolerance. In contrast, maize plants in which ZmMAPKKK21 was knocked out were more sensitive to water deficiency, and have a smaller root system and a lower survival rate after rewatering than wild type plants. These results suggest that ZmMAPKKK21 is a positive regulator for drought response in J24, which provides insights into the molecular mechanism underlying the strong drought resistance of J24. • We first performed a phenotypical characterization to confirm the impressive drought resistance of maize Jing24 under drought stress. • A comprehensive analysis of RNA-Seq and WGCNA uncovered a spectrum of shared and distinct differentially expressed genes under various drought scenarios, indicating the line-, tissue- and developmental stage-specific response to drought. • The gene ZmMAPKKK21 is a positive regulator for drought response in Jing24, with significant contribution to ABA sensitivity, root architecture, survival rate upon rewatering.