Screening Of Drought-Tolerance Rhizobia Of Soybean And Its Proteomics

In this study, seven soybean rhizobia strains with drought-tolerance were isolated by drought stress under laboratory and soil-pot experiment from twenty-one rhizobia strains (two reference strains included), which were obtained from the Huanghuaihai area. These strains with drought-tolerance grew better and were good at nodulating and nitrogen fixation under drought stress. Then, the influences on the physiological and biochemical indexes of soybean inoculated with the rhizobium under drought stress were studied. Proteomic technique was used to analyze the drought-tolerance mechanism preliminarily. The results would be a guide for the screening, application, and nitrogen fixation of effective rhizobial strains with drought-tolerance in dry areas. Detailed results were listed as the following.Drought condition in the experiment was simulated by PEG6000. The results showed that, growth of the tested strains were increasely inhibited along with the increasing of the drought degree. The OD of seventeen strains would reduce upto more than 70% under 25% of PEG6000. The strains were seriously inhibited. Under the same condition of PEG6000, the OD of B. japonicum USDA110, B. japonicum 4788, B. japonicum 4792, B. japonicum 4534, S. fredii 4632, S. fredii 4780, S. fredii 4796 less significantly decreased than the others, inclicating a good ability of drought tolerance. Secondary screening by soil-pot experiment with simulated drought environment followed. The results revealed that, three strains of B. japonicum 4788, B. japonicum 4792 and B. japonicum USDA110 were good at nodulating, nitrogen fixation and plant growth promoting, and would be drought-tolerance rhizobia.Several parameters related with drought resistance of plant were determined when B. japonicum 4792 was inoculated under the condition mentioned above. The results showed that, the contents of betain, chlorophyll and SOD in plant increased but MDA decreased compared with the uninoculated control. Thus, the inoculation of rhizobia was beneficial for accumulation of drought-tolerance materials in soybean plant and improvement of drought-resistant for plants.The protein expression profiles of B. japonicum 4792 were analyzed after the strain was exposed to PEG6000. The results showed that B. japonicum 4792 had ten up-regulated proteins and thiry-eight down-regulated proteins with significant difference. The differential proteins were analyzed by MALDI-TOF-MS and twelve of them were identified. Most of them were associated with stress protein, translation, metabolism and signal transduction.Among the identified proteins from B. japonicum 4792 in this study, S-adenosylmethionine synthetase,Stress-response protein and DNA-binding response protein, and ATP synthase subunit beta were up-regulated. Because S-adenosyl methionine synthetase was closely relatated with the transmission of drought-stress signal, it was hypothesized that the genes of drought defense were regulated to strengthen resistance of drought stress. Furthemore, stress protein and DNA-binding stress response could stabilize protein and peptide, it could heighten the resistance to stress by degrading the damaged protein and protecting DNA from various damage so as to help strains grow in the stress environment. Additionlly, ATP synthase subunit beta could provide more energy for strains to adapt to the impact of stress. So,it was sopposed that the aboved three proteins in responses to drought stress may be one of the main mechanisms that help B. japonicum 4792 had drought-tolerance ability.