Improved Rice Resilience To Drought By Endophytic Streptomyces Albidoflavus OsiLf-2

As one of the important food crops,rice consumes the most water,and its production is severely affected by drought.Therefore,it is of great significance to improve the drought resistance of rice.Plant endophytes live inside plant tissues,and can co-evolve with the host and reciprocal symbiosis,which can enhance the plant’s resistance.In this study,the endophytic actinomycete Streptomyces albidoflavus OsiLf-2（hereinafter referred to as OsiLf-2）isolated from the leaves of rice and rice were used as experimental materials.Rice（indica rice 9311）was treated by seed embedding with spore suspension（hydroponics experiment）and leaf spraying（soil culture experiment）,respectively.The OsiLf-2 treated rice（E+）and untreated control（E-）were set to analyze the effect of OsiLf-2 on the drought resistance of rice.In the hydroponic experiment,20%polyethylene glycol 6000（PEG）was used to simulate drought stress.In the soil culture experiment,natural drought stress was carried out.This study aims to explore the physiological mechanism of endophytic actinomycetes in regulating drought resistance in rice,and has achieved the following research results:（1）OsiLf-2 can alleviate the effects of drought stress on rice growth.After 7 days of PEG-simulated drought stress treatment,the growth physiological indexes of the seedlings in the E+rice were significantly higher than those in the E-group,such as the fresh weight of rice tissues above and below the ground increased by 47.8%and47.6%,respectively.Further measurement showed that the chlorophyll content and net photosynthetic rate of the seedlings in the E+group were significantly increased by30.6%and 12.5%compared with the E-group.After the natural drought stress treatment,the rice yield-related indicators of the E+group were significantly higher than those of the E-group,especially the spike length and spike number increased by13.8%and 46.6%,respectively.The indicated that under drought stress,OsiLf-2 can help rice increase its photosynthetic efficiency and stabilize the yield.（2）OsiLf-2 can help host rice to maintain the integrity of cell membranes under drought conditions.After PEG-simulated stress treatment for 1.5 hours,the leaves and roots of E-seedlings had already accumulated H₂O₂,while that in E+group didn’t show this accumulation.At the same time,the activities of antioxidant enzymes（SOD,POD,CAT）in the E+group increased,the electrical conductivity and malondialdehyde content of the seedlings were significant ly lower than those in the E-group.These indicate that OsiLf-2 can reduce excessive ROS caused by drought stress,alleviate damage to the seedling cell membrane,and maintain the integrity of the cell membrane.（3）OsiLf-2 can increase the content of osmotic adjustment substances in rice under PEG-simulated drought stress treatment.Under PEG stress conditions,the proline and soluble sugar content of rice seedlings in the E+group increased.This indicates that OsiLf-2 may be maintain the water-holding capacity of cells or tissues by increasing the content of osmotic adjustment substances,thus reducing the damage caused by drought to rice.（4）Under PEG-simulated drought stress treatment,OsiLf-2 increased the expression of drought resistance-related genes in rice.Under the conditions of PEG stress,the expression levels of Os LEA3,Os P5CS1,Os P5CS2,Os MYB4,and Os WRKY11 in rice seedlings of E+group were improved,thus enhancing the drought resistance performance of rice.In summary,the rice endophytic OsiLf-2 increased the osmotic-adjustment ability,antioxidant enzyme activity,photosynthetic characteristics and drought resistance-related gene expression of rice seedlings under drought stress,promoted the accumulation of rice seedling biomass and t he development of the root system,and improved the yield of rice.This study provides a theoretical basis for the further development of OsiLf-2 into a bio-fertilizer for improving the stress resistance of rice.