Inoculation of abscisic acid-producing endophytic bacteria enhances salinity stress tolerance in Oryza sativa

Salinity hinders plant growth and results in reduced crop yield. The use of plant growth-promoting endophytic bacteria is an eco-friendly strategy to counteract such stresses and confer tolerance to the host. Endophytic bacteria have been recognized for their active role in auxin production; however, little is known about their ability to produce abscisic acid (ABA). In recent studies, the bacterial endophyte Bacillus amyloliquefaciens RWL-1 has been found to produce ABA, and as such, has the potential to increase plant resistance to salinity stress. Results showed that RWL-1 produced varying concentrations of ABA (0.32 ± 0.015-0.14 ± 0.030 ng mL−1) under normal and saline conditions. The ability of RWL-1 to produce ABA was reduced in response to increasing salinity; however, it maintained its growth by up-regulating production of essential amino acids (glutamic acid and proline). To further investigate the potential of this endophytic bacterium, a plant-microbe interaction experiment was conducted which showed that RWL-1 inoculation significantly increased growth attributes of rice plants as compared to non-inoculated control plants under salinity stress. Micrographs also revealed active symbiosis of RWL-1 with plant roots under normal and salinity stress conditions. The essential amino acids (glutamic acid, aspartic acid, phenylalanine, proline, and cysteine) were significantly up-regulated by RWL-1 inoculation under salinity stress. In addition, the stress-sensitive endogenous ABA levels were significantly reduced, whereas the levels of endogenous salicylic acid were significantly higher in RWl-1-inoculated plants than in control plants exposed to the same level of salinity stress. The current findings suggest that the phytohormone-producing abilities of endophytic bacteria can increase plant resistance to salinity, in turn improving agricultural productivity.