Transcriptome analysis reveals dynamic changes in the salt stress response inSalix

Soil salinization is a serious ecological problem worldwide and information regarding the salt tolerance mechanisms ofSalixis scarce. To elucidate the dynamic changes in the molecular mechanisms ofSalixunder salt stress, we generated gene expression profiles and examined changes in the expression of those genes. RNA-Seq was used to produce six cDNA libraries constructed from the leaves ofSalix x jiangsuensisCL 'J2345' treated with NaCl for 0, 2, 6, 12, 24 and 48 h. In total, 249 million clean reads were assembled into 12,739 unigenes, all of which were clustered into 10 profiles based on their temporal expression patterns. KEGG analysis revealed that as an early defense response, the biosynthesis pathways of cutin, suberin and wax, which are involved in cell wall structure, were activated beginning at 2 h. The expression of secondary metabolism genes, including those involved in the phenylpropanoid, flavonoid, stilbenoid, diarylheptanoid and gingerol pathways, peaked at 6 h and 24 h; the upregulated genes were mainly involved in plant hormone pathways and beta-alanine, galactose and betalain metabolism. We identified roles of key phytohormones and found ETH to be the major signaling molecule activating TFs at 12 h; ETH, ABA, IAA and SA were the key molecules at 24 h. Moreover, we found that the upregulated genes were associated with elevated levels of amino acids, sucrose, inositol, stress proteins and ROS-scavenging enzymes, contributing to the maintenance of water balance. This research constitutes the first detailed analysis of salt stress-related mechanisms inSalixand identifies potential targets for genetic manipulation to improve yields.