Plant growth-promoting endophyte Sphingomonas sp. LK11 alleviates salinity stress in Solanum pimpinellifolium

Salinity stress can be detrimental to the growth and yield of plants. The adverse effects of salinity can be ameliorated with the application of plant growth-promoting endophytic bacteria (PGPEB). The concomitant beneficial effects of exogenous jasmonic acid (JA) in synergism with PGPEB have been well-established; however, its physiological responses under salinity stress have least been understood. In initial screening, PGPEB (Sphingomonas sp. LK11) was grown with or without JA and sodium chloride. LK11 did not significantly compromise its growth and physiological processes such as biosynthesis of cell wall-related amino acids (aspartate, glutamate, and alanine) during JA treatment under salinity stress. This improved growth performance during salinity stress was mainly due to the expression of glutathione-related genes in LK11 genome. PGPEB counteracting salinity stress can be vital trait to improve crop's growth and tolerance. In plant-microbe interaction, the interplay of JA and LK11 and their synergistic effects on the growth of wild-type Solanum pimpinellifolium and non-isogenic mutant (Got-3) plants under salinity stress were assessed. Combined LK11-JA applications significantly improved the shoot/root growth in both wild-type and Got-3 tomato plants with or without salinity stress. Combined treatment of LK11-JA responded well to salinity stress by significantly regulating glutathione contents in wild-type and Got-3 plants. Endogenous stress-responsive abscisic acid contents were significantly low in sole and combined LK11-JA applications during salinity as compared to sole saline conditions in both types of plants. Relatively high levels of salicylic acid (SA) and low levels of JA showed the impaired stress tolerance and growth with/without salinity stress in Got-3 plants. In contrast, wild-type plants showed relatively higher JA and lower SA levels in response to combined LK11-JA treatments under salinity stress. These findings indicate that combination of PGPEB and JA is not essentially harmful to plants; however, both can reprogramme crop plant responses to overcome the adverse effects of salinity stress.