Research On The Proliferation Mechanism Of Allelopathic Potential Myxococcus Xanthus In Allelopathic Rice Rhizosphere

The academic view on that the interaction between soil microbes and plant allelochemicals leads to the final allelopathic potential on the targets have been widely accepted.Our previous found that the phenylalanine ammonia lyase?PAL?gene located on rice chromosome 2 function in regulation of the biosynthesis of phenolic acids in allelopathic rice PI312777,inhibiting of PAL-2 gene in PI312777 leads to reduce phenolic acids concentrations in rice and also decrease allelopathic potential on weed,while the biodiversity on bacterium from rice rhizosphere was also reduced,expecially on Myxococcus sp.that belongs to myxobacterium.In addition,It was found that the rhizosphere soil of allelopathic rice PI312777 contained more population number of Myxococcus than that of non-allelopathic rice rhizosphere soil,which suggests that Myxococcus plays an important role in the rhizospheric biological process of allelopathic rice in suppression of weeds.In order to further elucidate the correlations between phenolic allelochemicals and Myxococcus xanthus from allelopathic rice rhizosphere in this study,allelopathic rice PI312777?PI?,non-allelopathic rice Lemont?LE?,PAL-2 overexpression transgenic PI312777?PAL-OE?,PAL-2 RNA interference transgenic PI312777?PAL-RNAi?were used as donor plants.Myxococcus xanthus that being separated from allelopathic rice PI312777 rhizosphere was used as the testing strain.At 5-leaf stage,rice root was taken to extract the compounds of secondary metabolites by using methanol,the methanol extracts was then filtered by using a 0.22-?m sterile filter,these filtrate was respectively mixed with or without M.xanthus strain to culture barnygrass seeds in the sterile soil,it was found that the single extracts from different rice took no significant difference on the inhibitory rate on the germination and growth of barnyardgrass.The extracts being mixed with Myxococcus xanthus stains showed obviously allelopathic inhibition on barnyardgrass,which is highest in the extracts of PAL-OE with M.xanthus,following by the wild type PI312777 root extracts with M.xanthus and lowest in that of PAL-RNAi.The real time quantitative PCR?qPCR?was also used to determine the population number of Myxococcus species in the soil under different treatments.The results showed that there was a positive correlation between the inhibitory rate on barnyardgrass and the population number of Myxococcus species in the soil.The findings suggested PAL-2 in regulation of phenolic acids synthesis in PI312777 and then influenced on the proliferation of Myxococcus species in rice rhizosphere,which is the dominant factor in the allelopathic potential on barnyardgrass.On this basis,the growth changes of Myxococcus xanthus in the medium containing with ferulic acid and cinnamic acid,as well as the changing concentration of ferulic acid and cinnamic acid under different culture hours was detected,the results indicated that both ferulic acid and cinnamic acid may act as signaling factors to promote cell proliferation of Myxococcus xantus,and adding with 0.10 mM ferulic acid in the medium demonstrated the most significant inductive effect.Further,a dimethyl labeling quantitative proteomic technique was used to investigate the proteins in Myxococcus xanthus cells and the secretions under the induction of ferulic acid.A total of 76 proteins was found simultaneously up-regulated and 56 proteins was simultaneously down-regulated in the M.xanthus being induced by 0.05 mM and 0.10 mM ferulic acid.These up-regulated proteins cover a wide range of biological functions,including cell growth,motility,signal response and transduction,metabolic process,production of secondary metabolites,social predation,transport and intracellular traffic.Some target proteins,including frzS,MXAN₂023,MXAN₃668 and MXAN₃339 were selected to detect their genes transcript level in the M.xanthus under the same treatment,and increasing of gene expression level of the four genes was found in the 0.10 mM ferulic acid inductive M.xanthus compared to the ferulic acid absent control.In addition,transcript level of five other gene menbers from frz multigene family including frzA?frzB?frzCD?frzE?frzG were also detected,the results showed that all the frz gene members were significantly up-regulated in the M.xanthus being induced by 0.10 mM ferulic acid.The above studies preliminarily revealed the proliferation mechanism of phenolic allelochemicals on the allelopathic potential M.xanthus,which provided theoretical references for understanding the underlying mechanism on the interaction of phenolic allelochemicals and myxobactrium.