The Disease-resistance And Growth-promoting Characteristics And Reacting Mechanisms Of Rice Endophytic Actinomycetes OsiSh-2 And OsiLf-2

Rice（Oryza sativa）is one of the most important food crops in the world,thus,ensuring the high and stable yield is the top priority for agricultural scientists.Endophytes,which colonize in the plant tissues,can positively interfere with plant physiological activities,such as promoting vegetative growth,increasing the biomass accumulation,and enhancing the resistance against various biological and abiotic stresses.However,the underlying molecular mechanisms of the interaction modes between endophytic actinomyces and their host plants are still scantily reported.In this study,two rice endophytic actinomycetes Streptomyces hygroscopicus OsiSh-2and Streptomyces albidoflavus OsiLf-2 were used as the research objects.The methods of physiology,biochemistry,molecular biology and proteomics were carried out to investigate the interaction mechanisms of the endophytic actinomycetes and rice symbionts in against the rice blast disease and growth regulation.As the results,the following innovative research achievements are obtained:（1）The bio-control efficiencies of OsiSh-2 and OsiLf-2 against rice blast disease in the field conditions have been confirmed.Foliar-spraying either the spore suspension or the cell-free culture filtrate of OsiSh-2 and OsiLf-2 could significantly reduce the disease index of rice blast in the field conditions.The spore suspension of OsiSh-2 presented the best biocontrol efficiency.Further studies show that the difference in disease resistance between these two strains might be related to the following factors:firstly,the differences in colonization ability in rice tissues.The colonization capability of OsiSh-2 was better than that of OsiLf-2 as the re-isolation rate of OsiSh-2 in rice shoot was 100%,while that was 71.4%of OsiLf-2.Secondly,OsiSh-2 can induce a faster and stronger immune response in rice.The lesion mimics were observed after OsiSh-2 foliar-spraying spore suspension treatment.The levels of H₂O₂accumulation,callose deposition,defense-related enzyme activities and the expression levels of defense-related genes were all significantly higher and earlier than those of OsiLf-2 treated rice.Lastly,OsiSh-2 can produce more secondary metabolites than OsiLf-2,especially antibiotic substances,while OsiLf-2 can produce more IAA and GA than OsiSh-2（2）The interaction mechanisms of OsiSh-2 on the disease resistance and growth promotion of host rice was analyzed.The biocontrol efficiency of OsiSh-2 spore suspension is quite stable in each-year field trials,and the disease control efficiency is relying on the applied dosage of OsiSh-2 spore suspension.The control efficiency of the seedling blast for OsiSh-2 was up to 45.3%,particularly the yield loss rate was reduced for 29.7%after the panicle blast,which was better than that in tricyclazole treated rice.The results show that the rice plant might be maintained in a“priming”state after OsiSh-2 treatment,because a large amount of H₂O₂accumulation and callose deposition were observed in rice leaves,which was at least 4 h earlier than that of unpretreated rice.The secretory proteome identified that many of the extracellular proteins secreted by OsiSh-2 are carbohydrates related hydrolytic enzymes,which may induce systemic disease resistance or directly inhibit the growth of pathogenic fungi.Basing on the Tandem Mass Tags labeled proteomics,the expression of proteins involved with growth and metabolism pathway in untreated rice after M.oryzae infection were significantly inhibited,while the expression level of more than90%of the defense-related proteins in OsiSh-2 treated rice were lower than those in untreated rice after M.oryzae infection.On the contrary,the related proteins in photosynthetic and nitrogen-metabolism pathways were up-regulated in OsiSh-2treated rice.Meanwhile,61.49%chloroplast localization proteins in the OsiSh-2treated rice were up-regulated after M.oryzae infection.The electron microscopy and physiological detection confirmed that the chloroplast size and starch grains in mesophyll cells were increased.These results suggested that OsiSh-2 can enhance the resistance against rice blast in rice plants by direct antagonism,indirect regulation of endogenous immune response,and maintain the normal growth and development of rice after rice blast infected by stimulating the chloroplast development.（3）The characteristics and mechanism of OsiLf-2 on the growth promotion in rice plants are elucidated.OsiLf-2 can significantly promote the growth and development of different rice varieties or even Arabidopsis thaliana.The biomass accumulation and root development of all detected host plants were better after OsiLf-2 treatment.OsiLf-2 can also improve the uptaking and utilizing of nitrogen by improving the activity of nitrogen metabolism-related enzymes in rice under low nitrogen stresses.The IAA produced by OsiLf-2 plays an important role in growth promotion in the host plants.After the IAA biosynthesis-related gene iaaM,the encoding gene for tryptophan 2-mono-oxygenase,was knockout from the DNA of OsiLf-2,the growth-promoting effect of rice and Arabidopsis thaliana by OsiLf-2treatment was significantly reduced.Thus,OsiLf-2 is a functional strain that can increase the plant’s stress tolerance and promote the growth and development of the host,and it has the prospect of being developed as a bio-fertilizer.In summary,this study takes rice and endophytic actinomycetes as the research object,aiming to reveal the new mechanisms of the interaction between endophytic bacteria and host in the aspects of anti-fungal diseases and growth regulation.At the same time,it provides a theoretical basis for the research of disease-resistant and grown-promoting species of rice mediated by microorganisms,and provides useful resources for the further development of new biological pesticides and biological fertilizers.