Characterization of Genes Associated with Salt Tolerance Using Transcriptome Analysis and Quantitative Trait Loci Mapping in Rice

We conducted transcriptome profiling analysis of O. glaberrima root using RNA-Seq at the control (OCR) and 100 mM NaCl treatment (OTR) at two time points (6 and 24 hours after treatment) to detect genes induced by salt stress. RNA-Seq analysis generated 102,690,698 sequence reads representing 30,388 predicted transcripts including 6,189 unannotated in Rice Annotation Project database. A total of 539 and 424 of differentially expressed genes (DEGs) were detected between OCR_6hours vs OTR_6hours and between OCR_24hours vs OTR_24hours, respectively (P < 0.001, q < 0.05). Among these DEGs, 262 genes showed constant differential expression at both 6 hours and 24 hours, and these included a bHLH containing protein, WRKY transcription factor, serine/threonine kinase, R2R3 MYB protein, and amino acid transporters. Interestingly, an enhanced seedling salt tolerant introgression line IL55 from a cross between a salt sensitive indica cultivar “Milyang23” and O. glaberrima harbors one DEG, Os02g0787300 encoding a mitogen activated protein kinase kinase (MAPKK) on chromosome 2. Analysis of the salt tolerance of the F2:3 lines from a cross between IL55 and Milyang23 indicated that the O. glaberrima segment on chromosome 2 containing the MAPKK gene was responsible for better shoot growth under salt stress at the seedling stage. The salt inducible genes will be evaluated in introgression lines (ILs) to understand whether the expression of these genes is associated with salt tolerance in ILs having the Milyang23 genetic background. Transcriptome sequence information in this study may be useful for developing DNA markers linked to salinity tolerance for MAS breeding.