Investigation of the ASR family in foxtail millet and the role of ASR1 in drought/oxidative stress tolerance.

KEY MESSAGE: Six foxtail millet ASR genes were regulated by various stress-related signals. Overexpression of ASR1 increased drought and oxidative tolerance by controlling ROS homeostasis and regulating oxidation-related genes in tobacco plants. Abscisic acid stress ripening (ASR) proteins with ABA/WDS domains constituted a class of plant-specific transcription factors, playing important roles in plant development, growth and abiotic stress responses. However, only a few ASRs genes have been characterized in crop plants and none was reported so far in foxtail millet (Setaria italic), an important drought-tolerant crop and model bioenergy grain crop. In the present study, we identified six foxtail millet ASR genes. Gene structure, protein alignments and phylogenetic relationships were analyzed. Transcript expression patterns of ASR genes revealed that ASRs might play important roles in stress-related signaling and abiotic stress responses in diverse tissues in foxtail millet. Subcellular localization assays showed that SiASR1 localized in the nucleus. Overexpression of SiASR1 in tobacco remarkably increased tolerance to drought and oxidative stresses, as determined through developmental and physiological analyses of germination rate, root growth, survival rate, relative water content, ion leakage, chlorophyll content and antioxidant enzyme activities. Furthermore, expression of SiASR1 modulated the transcript levels of oxidation-related genes, including NtSOD, NtAPX, NtCAT, NtRbohA and NtRbohB, under drought and oxidative stress conditions. These results provide a foundation for evolutionary and functional characterization of the ASR gene family in foxtail millet.