Comparative Cytological and Gene Expression Analysis Reveals Potential Metabolic Pathways and Target Genes Responsive to Salt Stress in Kenaf (Hibiscus cannabinusL.)

Salt stress represents the most unfortunate abiotic stress factor in agricultural areas worldwide and contributes a severe reduction in growth, development, and yield of crop plants. Kenaf is a salt-tolerant crop. However, molecular mechanisms of salt stress tolerance in kenaf are not well elucidated. In the present study, seed germination parameters and cytological and transcriptome responses of leaves from two cultivars of kenaf (salt-tolerant P3A and salt-sensitive P3B) were analyzed between 250 and 0 mM NaCl treatments. Results indicated that under salt stress cultivar P3A had higher seed germination energy, germination index, and germination percentage with the less relative rate of salt damage than cultivar P3B. Furthermore, cytological studies indicated swelling and vacuolization of chloroplast and thylakoid in cultivar P3A under the influence of salt stress; however, chloroplast and thylakoid were degraded in cultivar P3B. Transcriptome analysis generated 8466 and 9333 differentially expressed unigenes (DEGs) (FDR <= 0.05 and log(2)FC >= 1) between salt-stressed and control treatments in cultivar P3A and cultivar P3B, respectively. Eight DEGs were selected randomly for quantitative real-time PCR to test the reliability of transcriptome sequencing results. Several genes encoding transcription factorsWRKY, AP2/EREBP, andHsfsfamilies and genes likeLEA, PsbA, PK, GSTs, NPR1,andTGAwere induced under salt stress, and expression levels were higher in the cultivar P3A compared to cultivar P3B. The GO enrichment and KEGG pathway analysis suggested that these DEGs were related to ionic homeostasis and transport, osmotic adjustment, water deficit response, antioxidants, ROS scavenging, cellular membranes protection, photo-damage repairing cycle of photosystem II, thylakoid part, plant hormone signal transduction pathway, and may be related to salt tolerance in kenaf.