Response mechanism in Populus x euramericana cv. '74/76' revealed by RNA-seq under salt stress

Populus spp., had the characteristics of rapid growth and high biological yield, is one of the major tree species in the world's afforestation and shelterbelt. But the growing soil salinization has become an important limited factor in the application of poplar planting. High-throughput sequencing technology was used to analyze the transcriptome of Populus x euramericana cv. '74/76' under treatments with different NaCl concentrations to determine the formation pathway of the poplar response to salt stress and further reveal the mechanism of resistance to salt stress, so providing theoretical guidance for the salt tolerant breeding of poplar. Sequencing obtained 31.5G sequencing data and generated a total of 263 million reads, which were mapped to 32,840 non-repeatable genes with a sequencing quality value of Q30 > 96.70%. After filtering, 292 and 3284 differentially expressed genes (DEGs) were obtained from 3 and 6% NaCl treatments, respectively. There were a large number of stress-induced genes differentially expressed under the 6% NaCl treatment. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis results showed that the salt resistance mechanism of poplar 107 was different under different NaCl treatments. Poplar 107, under a high NaCl concentration treatment had a more salt resistant metabolic pathway, which included the citric acid cycle [tricarboxylic acid (TCA) cycle], terpenoid backbone biosynthesis, flavone and flavonol biosynthesis, carotenoid biosynthesis, zeatin biosynthesis, calcium signaling pathway, and other important salt-related pathways. We excavated the genes that affected the electron transport involved in the process of photosynthesis under salt stress and the key enzyme genes in response to salt stress involved in glutathione and terpenoid backbone metabolism. A total of 52 transcription factors (TFs), including 24 new TFs closely related to the salt stress response mechanism, were identified in the co-expression genes. This result provided important theoretical guidance for the establishment of the poplar salt resistance database, excavation of salt tolerant genes, and breeding of new species of poplar by means of molecular biology.