Integration of mRNA and miRNA analysis reveals the molecular mechanism of potato (Solanum tuberosum L.) response to alkali stress

The continuing increase in the global saline-alkali land area has made saline-alkali stress the principal abiotic stress limiting plant growth. Potato is the most important non-grain crop, and its production is also severely limited by saline-alkali stress. However, few studies have addressed the mechanism of saline-alkali tolerance of potato with a focus on its response to neutral salt NaCl stress, or its response to alkali stress. Recently, miRNA-mRNA analyses have helped advance our understanding of how plants respond to stress. Here, we have characterized the morphological, physiological, and transcriptome changes of tissue culture seedlings of potato variety "Qingshu No. 9" treated with NaHCO3 (for 0, 2, 6, and 24 h). We found that the leaves of tissue culture seedlings wilted and withered under alkali stress, and the contents of ABA, BRs, trehalose, and lignin in roots increased significantly. The contents of GAs decreased significantly. Subsequently, miRNA-seq analysis results identified 168 differentially expressed miRNAs (DEMIs) under alkali stress, including 21 exist miRNAs and 37 known miRNAs from 47 families and 110 novel miRNAs. The mRNA-seq results identified 5731 differentially expressed mRNAs (DEMs) under alkali stress. By miRNA-mRNA integrated analysis, were obtained 33 miRNA-target gene pairs composed of 20 DEMIs and 33 DEMs. Next, we identified the "phenylpropanoid biosynthesis", "plant hormone signal transduction", and "starch and sucrose metabolism" pathways as necessary for potato to respond to alkali stress. miR4243-x and novel-m064-5p were involved in the response of potato to alkali stress by their negative regulatory effects on shikimate O-hydroxycinnamoyltransferase (HCT) and sucrose-phosphate synthase (SPS) genes, respectively. The expression results of miRNA and mRNA were verified by quantitative real-time PCR (qRT-PCR). Our results clarify the mechanism of potato response to alkali stress at the miRNA level, providing new insights into the molecular mechanisms of potato's response to alkali stress. We report many candidate miRNAs and mRNAs for molecular-assisted screening and salt-alkali resistance breeding.