Improved Resistance Of The Host To Fe-deficiency By Rice Endophytic Streptomyces Hygroscopicus OsiSh-2

Iron(Fe)deficiency is a common adversity stress in rice growth.It usually causes a severe reduction of rice yield and low Fe concentration in grains.Compared with the traditional methods of Fe deficiency control,biological methods are environmentally friendly and easy to promote.An endophytic actinomycetes Streptomyces hygroscopicus OsiSh-2,was screened by our previous laboratory work and the results showed that it has an efficient Fe absorption ability under the Fe deficiency.Therefore,it can inhibit pathogen M.oryzae by competing for Fe.This study takes OsiSh-2 as the research object to explore its effect and mechanism of endophytic actinomycete OsiSh-2 on rice growth under Fe deficiency.Related contents and results are as followed:1.Osish-2 can alleviate the effect of Fe deficiency on rice growth.The rice inoculated with OsiSh-2(E+)or non-inoculated with OsiSh-2(E-)were cultured in the hydroponic solution which was either supplied with 2 mg L-1(full strength,+Fe)or 0 mg L-1(depleted,-Fe),respectively.It was found that OsiSh-2 could significantly increase the growth-related indexes of rice under Fe deficiency,including the plant height,root length,fresh weight and dry weight of aboveground and underground parts,chlorophyll content and photo synthetic rate,especially the photo synthetic rate increased by 92.8%.Compared to E-rice,the expression levels in E+rice of HernAl and atpE were up-regulated by 0.51 and 0.37-fold,respectively.Moreover,Osish-2 had the same effect on rice under Fe sufficiency.It’s showed that rice biomass increased significantly,especially the photosynthesis rate increased by 35.5%.The expression of HernAl and atpE increased 0.51 and 0.47-fold respectively,compared with E-rice.What’ more,it was found that the photo synthetic rate increased by 11.1%and tiller number of E+rice rose by 24.4%during the tillering stage,compared with E-rice.In the ripening stage,the grain number,grain weight and grain length all increased,especially the grain weight increased 14.4%.2.OsiSh-2 enhanced the Fe aborption and Fe accumulation in rice.Under Fe deficiency,compared to E-rice,the Fe absorption rate and Fe accumulation in aboveground and underground parts of E+rice increased significantly by 14.0%,59.1%and 64.6%respectively.The expression level of OsFRDL1 gene in E+rice was significantly up-regulated by 0.76-fold,compared with E-rice.These results indicate that indicated that OsiSh-2 could promote the Fe absorption efficiency and enhanced the ability of Fe translocation to different tissue parts of rice under Fe deficiency.They also suggest that OsiSh-2 has a continuously beneficial impact on Fe absorption and accumulation in rice from the seedling stage to the ripening stage.Corresponding,the Fe concentration of grain in E+rice increased by 41.9%compared with E-rice.Corresponding,the Fe concentration in the E+rice grain increased 41.9%under Fe deficiency compared with that of E-rice.3.There are two strategies that OsiSh-2 enhances Fe absorption to ensure rice growth under Fe deficiency.The production of different types of siderophore in rice root exudates,the expression levels of genes related to phytosiderophore synthesis(OsNASl and OsNAS1)and phytosiderophore transporter(OsYSL15)were measured.Results showed OsiSh-2 increase the production of total siderophore(rose through nearly 44.4%)by secreting its unique hydroxamic siderophore.Thus,the Fe3+absorption in rice is enhanced.Because of the character of OsiSh-2,the production of phytosiderophore is reduced,which saves more energy for rice growth.In another way,the acidification ability,the Fe3+reductase and the expression of genes related to Fe3+reductase synthesis(OsFRO1 and OsFRO2)and Fe2+transporter(OsIRT1 and OsNRAMP1)were measured.Results indicated that OsiSh-2 could enhance Fe3+reductase activity and rhizospheric acidification capacity in the rice rhizosphere through secreting Fe3+reductase and reducing environmental pH under Fe deficiency.Additional Fe2+transported into the rice.To sum up,rice endophytic actinomycete OsiSh-2 can support rice to absorb Fe from the environment by enhancing the ability of Fe3+-chelation and Fe3+-reduction.These efforts will further enhance the Fe translocation in rice and guarantee the Fe supplement in various organizations of rice.It would reduce the adverse effects of Fe deficiency in rice to ensure its growth.This work provides a new basis for the OsiSh-2-rice interaction to jointly resist adversity stress,and provides a theoretical basis for the development of biological fertilizers suitable for Fe deficiency.