Transcriptional response of cultivated peanut (Arachis hypogaea L.) roots to salt stress and the role of DNA methylation.

Our study unravels a complex multi-layered molecular response of peanut roots to salinity, where reprograming of gene-expression is partly executed by changes in methylome via RdDM pathway and exerted through transcription factors. Peanut (Arachis hypogaea L.) is a major oilseed crop of global importance, whose production is severely impacted by salinity. Here, we have explored the transcriptional response of peanut roots to salinity stress using deep sequencing. Further, we have unravelled the salinity-induced changes in peanut root methylome. When peanut seedlings were grown under high-salt conditions for 7 days, their root and shoot growth was significantly impaired. A large-scale transcriptional reprogramming was recorded where 1926 genes were down- and 3260 genes were up-regulated due to salt stress in peanut roots. The molecular response of peanut root comprised several layers of regulators, which included the genes related to ion transport, osmolyte accumulation, signal transduction, and salt stress-responsive genes. Several negative regulators are also differentially expressed in peanut roots, which may contribute to its susceptibility. This response is regulated by a large number of transcription factors (TFs) and epigenetically by changes in DNA methylation. The DNA methylation changes in roots were highly complex and context dependent when exposed to salt stress. An inverse relationship between the changes in gene expression and methylation status was partially observed for several important gene sets and TFs. A treatment with 5'-azacytidine recovered the inhibitory impact of salt stress in peanut roots. Thus, a complex multilayered molecular response to salinity in peanut roots was observed. A part of this response may be modulated by the reprogramming of RNA-directed DNA methylation pathway. This investigation also serves as a resource for future gene-mining and methylation studies for improving peanut resistance to salt stress.