Saline-alkali stress tolerance is enhanced by MhPR1 in Malus halliana leaves as shown by transcriptomic analyses

qRT-PCR analysis showed that MhPR1 was strongly induced by saline-alkali stress. Overexpression of MhPR1 enhanced tolerance to saline-alkali stress in transgenic tobacco (Nicotiana tabacum L.) and apple calli. Abstract: Soil salinization seriously threaten apple growth in Northwest loess plateau of China. Malus halliana has developed special system to adapt to saline-alkali environmental stress. To obtain a more detailed understanding of the adaptation mechanisms involved in M. halliana, a transcriptomic approach was used to analyze the leaves' pathways in the stress and its regulatory mechanisms. RNA-Seq showed that among the 16,246 investigated unigenes under saline-alkali stress, 7268 genes were up-regulated and 8978 genes were down-regulated. KEGG analysis indicated that most of the enriched saline-alkali-responsive genes were mainly involved in plant hormone, calcium signal transduction, amino acids, carotenoid and flavonoids biosynthesis, carbon and phenylalanine metabolism, and other secondary metabolites. Expression profile analysis by quantitative real-time PCR confirmed that the maximum up-regulation of MhPR1 under saline-alkali stress was 7.1 folds in leaves. Overexpression of MhPR1 enhanced tolerance to saline-alkali stress in transgenic tobacco (Nicotiana tabacum L.) and apple calli. Taken together, our results demonstrate that MhPR1 encodes a saline-alkali-responsive transcriptional activator and provide valuable information for further study of PR1 functions in apple.