| Soybean is an important source of food,fodder and biofuel.The legume-rhizobia symbiosis is the most important contributor of symbiotic N in natural and agricultural ecosystems.Approximately 50%of the world’s arable land is considered acidic with an underlying problem of aluminum toxicity.And aluminum toxicity has been reported in 67%of the world’s acidic soils.Aluminum toxicity can inhibit the growth of rhizobium and host and inhibit their symbiosis,resulting in low biological nitrogen fixation efficiency and decreased crop yield.Due to the toxicity and wide distribution of aluminum,it has become the main factor limiting the growth of soybean and biological nitrogen fixation in acid soils.The resistance of plants to adversity can be enhanced by inoculation of stress resistant rhizobium to build symbiotic relationship with plants.Meanwhile,aluminum tolerant microorganisms play an indispensable role in soil bioremediation.Therefore,it is of great significance to screen the aluminum-tolerant rhizobium and explore its mechanism.In this study,nodules of two soybean genotypes BX10(aluminum tolerant type)and BD2(aluminum sensitive type)grown on acid red soil were used as materials to screen out aluminum-tolerant rhizobium,and the genera of rhizobium were identified by nodulation test,16S rDNA and housekeeping gene phylogenetic analysis and physiological and biochemical reactions.The results showed that RFS-1 and RFS-2 could grow normally at 350 μmol/L and 200 μmol/L respectively.Next,RNA-Saq technology was used to provide a detailed analysis of the global transcriptional response of RFS-1 when the cells were exposed to 350 μmol/L of aluminum.Total of 1752 genes were differentially expressed(Fold Change>2.00)with 844 genes were up-regulated while 908 genes were down-regulated,in comparing to control with no aluminum added in the culture.Based on Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway analysis,the majority of genes encoding for metabolism such as carbon,glycine,serine and threonine,pyruvate metabolism,TCA cycle,environmental information processing such as bacterial secretion system,HIF-1 signaling pathway,genetic information processing such as RNA polymerase、RNA degradation,were up-regulated.Further analysis revealed that specific response genes were associated with oxidative phosphorylation,TCA cycle,pyruvate metabolism,exopolysaccharides synthesis,and iron transporters.At the same time,the content of exopolysaccharides was determined,and it was found that the yield of exopolysaccharides was significantly increased under high aluminum stress.In conclusion,the up-regulated expressed genes responsible for exopolysaccharides synthesis,TCA cycle and siderophore transporter may be related to the resistance of RFS-1 to aluminum,which provides further insight and help us to understand on the resistance of Rhizobium toward aluminum. |
