Transcriptome profiling of unigenes participating in salt tolerance in purslane (Portulaca oleracea) under salinity stress

The second generation of RNA-sequencing was done on the leaves of salt-tolerant ('PL') and salt-sensitive ('LCL') purslane (Portulaca oleracea) genotypes. Twenty-four RNA libraries were obtained at four different time intervals (0 h, 1 h, 24 h, and 72 h) during salinity stress. Compared with control, at 1 h, 24 h, and 72 h of 200 mM NaCl treatment, 7407, 2499, and 7597 of differential expression genes (DEGs) were qualified in 'LCL', and 8861, 7974, and 10349 in 'PL' the Kyoto Encyclopedia of Genes and Genomes (KEGG)- and Gene Ontology-based pathway studies displayed that salt stress response of purslane was a complex metabolic regulation process. Two kinds of analyses, especially KEGG, showed that salt stress affected gene expression linked with metabolism of fatty acid. Two fatty acid metabolism pathways, "alpha-linolenic acid metabolism" and "fatty acid degradation" were downregulated in two genotypes at 24 h vs 0 h and 72 h vs 0 h of NaCl stress. Another fatty acid metabolism pathway, "biosynthesis of unsaturated fatty acids", was only upregulated at 24 h vs 0 h and 72 h vs 0 h of NaCl stress in 'PL'. Upregulated expressions of FAD2, SAD, ACX2, and CLKR27 in "biosynthesis of unsaturated fatty acids" pathway might be associated with salt tolerance of 'PL' in purslane. Among these, upregulation of FAD2 and SAD might be beneficial to the accumulation of polyunsaturated fatty acids, upregulation of ACX2 might promote the plant growth under salt stress in salt-tolerant purslane genotype. The results are of great significance for further screening salt-tolerant and high-quality purslane genotypes.