Integrated physiological, transcriptomic and proteomic analyses revealed molecular mechanism for salt resistance in Solidago canadensis L.

Solidago canadensis is an invasive plant around the world, and it has been found to have successfully invaded saline soils. To dissect the salt acclimation mechanisms in S. canadensis, we analyzed the transcriptome and proteome of salt-treated S. canadensis for 0, 1, 2, 4, and 8 days. We identified a total of 7496 differentially expressed genes (DEGs), of which 662, 2569, 3866 and 399 were identified in different salt-treated stages. We identified 0, 14, 76 and 337 differentially expressed proteins (DEPs) in different salt-treated stages, of which sum up to 427 DEPs. These results indicated that the transcriptome of S. canadensis changed greatly in the early stage under salt stress, whereas the proteome changed greatly in the late stage. Weighted gene co-expression network analysis (WGCNA) identified 28 modules which consisted of co-expressed DEGs and 5 modules which consisted of co-expressed DEPs. Salt stress altered physiological traits of S. canadensis, including proline content, photosynthesis and three antioxidant enzyme activity, and some genes and proteins were involved in these physiological processes. For example, 'brown' module of genes was found to be highly correlated with proline accumulation. Two transcription factor genes, CL13369.Contig2_All (mTERF) and Unigene22959_All (MYB44), were presented in 'brown' module as hub genes. We found 'turquoise' and 'blue' module of proteins with most of DEPs involved in photosynthesis, antioxidant mechanisms and secondary metabolism. The changes in gene and protein expression indicated that S. canadensis may transfer energy into the protective system in response to salt stress, at the cost of photosynthesis and secondary metabolic processes. Our study provided the molecular mechanisms that may explain acclimatory process of S. canadensis to salt stress and provided many candidate genes and proteins for further research.