Genome-wide characterization of homeodomain-leucine zipper genes reveals RsHDZ17 enhances the heat tolerance in radish (Raphanus sativus L.).

Homeodomain-leucine zipper (HD-Zip) transcription factors are involved in various biological processes of plant growth, development, and abiotic stress response. However, how they regulate heat stress (HS) response remains largely unclear in plants. In this study, a total of 83 RsHD-Zip genes were firstly identified from the genome of Raphanus sativus. RNA-Seq, RT-qPCR and promoter activity assays revealed that RsHDZ17 from HD-Zip Class I was highly expressed under heat, salt, and Cd stresses. RsHDZ17 is a nuclear protein with transcriptional activity at the C-terminus. Ectopic overexpression (OE) of RsHDZ17 in Arabidopsis thaliana enhanced the HS tolerance by improving the survival rate, photosynthesis capacity, and scavenging for reactive oxygen species (ROS). In addition, transient OE of RsHDZ17 in radish cotyledons impeded cell injury and augmented ROS scavenging under HS. Moreover, yeast one-hybrid, dual-luciferase assay, and electrophoretic mobility shift assay revealed that RsHDZ17 could bind to the promoter of HSFA1e. Collectively, these pieces of evidence demonstrate that RsHDZ17 could play a positive role in thermotolerance, partially through up-regulation of the expression of HSFA1e in plants. These results provide novel insights into the role of HD-Zips in radish and facilitate genetical engineering and development of heat-tolerant radish in breeding programs.