Genome-Wide Identification of Differentially Expressed Genes Reveals Complex Heat Stress-Responsive Regulatory Network in Radish (Raphanus sativus L.) Root

Heat stress (HS) causes detrimental effects on plant morphology, physiology and biochemistry that lead to drastic reduction in plant biomass production and economic yield worldwide. To date, little is known about HS-responsive genes involved in thermotolerance mechanism in radish. In this study, a total of 6,600 differentially expressed genes (DEGs) from the CK and Heat24 cDNA libraries of radish were isolated by high-throughput sequencing. With Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, some genes including MAPK, DREB, ERF, AP2, GST, Hsf and Hsp were predominantly enriched in signal transductions, metabolic pathways, biosynthesis and abiotic stress-responsive pathways. These pathways play significant roles in reducing stress-induced damages and acquisition of thermotolerance in radish. Expression patterns of 24 candidate genes were validated by reverse-transcription quantitative PCR (RT-qPCR). Based mainly on the analysis of DEGs combining with the previous miRNAs analysis, the schematic model of HS-responsive regulatory network was proposed. To counter the effects of HS, a rapid response of the plasma membrane leads to the opening of specific calcium channels and cytoskeletal reorganization, after which HS-responsive genes are activated to repair damaged proteins and ultimately facilitate further acquisition of thermotolerance in radish. These results could provide fundamental insight into the regulatory network underlying heat tolerance in radish and facilitate further genetic manipulation of thermotolerance in root vegetable crops.