Insights into Salt Stress-Induced Biochemical, Molecular and Epigenetic Regulation of Spatial Responses in Pigeonpea (Cajanus cajan L.)

Abstract

Pigeonpea (Cajanus cajan L.) is a rich source of nutritionally good quality proteins, carbohydrates, minerals, and vitamins. However, environmental stresses adversely affect its productivity. Only limited reports are available on biochemical/physiological responses of pigeonpea under salt stress. The objectives of the present study were to screen pigeonpea germplasm accessions for salt stress tolerance, followed by understanding their biochemical, epigenetic and molecular responses. Based on germination, growth, and vigor of seedlings under salt stress, the most contrasting pair of salt-responsive genotypes (ICP1071- most salt-sensitive, and ICP7- most salt-tolerant) were selected. Three-week-old seedlings subjected to 250 mM NaCl stress for 7 days showed a significant increase in proline and reducing sugar contents in the case of ICP7, whereas a considerable increase in cell wall-degrading enzyme activity and protein oxidation was observed in ICP1071. Superoxide dismutase, peroxidase, and glutathione reductase activity increased considerably in shoots of ICP7. We observed the CcCYP gene to be upregulated in root, whereas CcCDR was upregulated in shoots of the salt-tolerant genotype to provide protection against the stress. The extent of DNA hypomethylation in the contrasting pigeonpea genotypes under salt stress was correlated with their salt tolerance level. Bisulfite sequencing of CcCDR revealed that methylation of three cytosine residues in CHH context in shoots of the ICP7 genotype due to salt stress results in 2.6-fold upregulated expression of the gene. With a 6.8% increase in methylation of the coding region of CcCDR, its expression level increased by 22%. To the best of our knowledge, this is the first report on a comprehensive study of salt-induced biochemical, epigenetic and molecular responses of pigeonpea, which might be useful in the development of improved salt-tolerant variety.