The Study Of Interaction Between Bradyrhizobium Sp. ORS278 And Rice

At present,plant colonization by rhizobia is found not only in leguminous plants but also in nonleguminous species such as rice.Regardless this association occurs widely,much remains unknown about rhizobial colonization to rice and molecular interaction between them.While rice plays a significant role in the world's food production,annual consumption of nitrogenous fertilizer not only consume large amounts of fossil energy,but also using a large amount of nitrogen brought serious ecological pollution.To study the interactions of the Bradyrhizobium symbiosis with rice to realize biological nitrogen fixation which plays an important role for ensuring food security and ecological construction.This study explores the relationship of Bradyrhizobium sp.ORS278 symbiotic interactions with rice through the Bradyrhizobium sp.ORS278 and rice inoculation experiment.At the same time,the mutants were used to study the effects of quorum sensing signal on the symbiosis between rhizobium and rice.Endogenous bacteria usually promote rice growth through the way of nitrogen fixation or IAA production.Through bioinformatics analysis,this study was found that the whole genome has the symbiotic nitrogen-fixing nifH gene necessary for the nitrogen fixation of rhizobia and the key enzymes for the synthesis of indole-3-acetic acid(IAA)pathway.Through the acetylene reduction experiment(ARA),it was proved that Bradyrhizobium sp.ORS278 was capable of nitrogen fixation,while Salkowski colorimetry and liquid mass spectrometry further confirmed that this rhizobia could produce indole-3-acetic acid.The above results indicated that Bradyrhizobium sp.ORS278 could promote the growth of rice.This study used logarithmic phase of Bradyrhizobium sp.ORS278 to inoculate Chinese rice under aseptic conditions,Chinese rice was cultivated around 15 days or 30 days with nitrogen free liquid medium.And then compare differences between the Bradyrhizobium sp.ORS278 inoculation of rice and the control group in plant height and weight.Preliminaryresearch suggests that Bradyrhizobium sp.ORS278 plays a certain role in promoting the growth of rice.The Bradyrhizobium sp.ORS278,which was labelled with the gfp gene,inoculated rice.Then the rice was cultivated 15 days after inoculation.To observe the Bradyrhizobium sp.ORS278 colonization in the fracture of lateral root epidermis through inverted fluorescence microscope.We have succeed isolated the Bradyrhizobium sp.ORS278 from the root surface disinfection of rice root with inoculation.This explains Photosynthetic Bradyrhizobium sp.ORS278 invades into the interior of the rice root from the fracture of rice roots.In order to explore the effect of Bradyrhizobium sp.ORS278 quorum sensing signaling on the symbiosis with rice.We used Bradyrhizobium sp.ORS278 quorum sensing signaling deficient mutant to evaluate the influence of quorum-sensing signaling in interaction between Bradyrhizobium sp.ORS278 and rice.Preliminary study shows that the strain of quorum sensing signaling influences the growth of rice compared with wild-type strains.Strain isolation experiments shows that quorum sensing signaling deficient mutant separation strains colony number compared to the number of wild type strains less two level,it reveals quorum sensing signaling affected the colonization of Bradyrhizobium sp.ORS278 in rice.In the process of rice cultivation experiments,we found the rice roots have nodules by accident.Thirteen strains of bacteria were isolated from the root tumor by surface disinfection,these bacteria respectively belong to Bacillus,Burkholderia,Chryseobacterium,Enterobacter,Pantoea,Bradyrhizobium sp.ORS278.When different types of bacteria were selected to be mixed together to inoculate rice,we found that these mixed strains had a strong pro-growth effect on rice.At the same time,Macpthora oryzae can be inhibited by the individual bacteria isolated from the nodule.Plant growth promoting and disease-resistant features make these bacteria have a great potential application value.As for the cause of the nodules and mechanism,it remains to be further explored.