The Feedback And Response Of Rhizospheric Microbial Communities Of Wild And Cultivated Soybean To Drought Stress

Drought is considered as the major abiotic stress limiting plant growth and yield worldwide.Soybean(Glycine max),as the main source of proteins and lipids,plays an essential role in China’s agricultural production.Drought is one of the main factors which threaten soybean yield through limiting the soybean growth and decreasing the number of flowers and pods.Therefore,in order to achieve high yield,it is important to improve drought resistance of soybean.Wild soybean(Glycine soja),the ancestors of cultivated soybean(Glycine max),has strong resistance and tolerance to environmental factors,and is the main source of vital germplasms for drought resistant breeding practices in China.As wild and cultivated soybean were grown in different habitats for long term,they have evolved different molecular,biochemical and physiological mechanisms to defend dehydration stress condition.Epigenetic and genetic factors playing the main role in the regulation of this process,but the role of rhizosphere microorganisms should not be ignored.Therefore,we studied the rhizosphere bacterial and fungal community structure and diversity of the wild and cultivated soybean and under drought stress condition,and further explored the mechanism of arbuscular mycorrhizal(AM)fungi improving the soybean resistance to drought stress.The results showed that wild soybean(Glycine soja)enhanced its drought resistance by accumulating the osmotic adjustment substances and increasing the expression of drought resistance gene.Higher sugar and prolin contents and NCED1 gene expression level were detected in Glycine soja than that in Glycine max.The response of rhizospheric fungi and bacteria of wild and cultivated soybean to the drought stress was significantly different.Under drought stress,the Shannon Wiener index of bacteria in wild soybean was increased significantly,while decreased in cultivated soybean,and the Shannon wiener index of fungi in both soybean genotypes was decreased.These results indicated that drought stress inhibit the diversity of rhizosphere fungi but notrhizosphere bacteria.Furthermore,Sulfitobacter sp.was onlydetected in wild soybean.Drought stress reduced the ratio of Rhizobium sp.in bacterium.There was an increase in the proportion of Bradyrhizobium sp.under drought stress condition in two soybean genotypes and the increase of Sphingomonas sp.(Band-16)only found in wild soybean genotype.We suspected that under unsuitable conditions,plants may establish certain relationship with rhizosphere microorganisms which can help them to cope with the abiotic stress conditions.But the mechanisms are still not well understood and need further study.The innoculation of AMF stimulated the root growth of both wild and cultivated soybean under drought stress,while the stimulation of the stems was not significant.The content of free proline and the activity of Catalase(CAT)in AMF incoculated soybeans were significantly higher than that in non-AMF soybean under drought stress condition,and the highest increase was found in the AMF innoculated wild soybean.However,the content of malondialdehyde(MDA)showed the opposite trend.The expression levels of GintAQPF1 and GintAQPF2 in AMF innoculated soybeans were increased significantly,and the expression level of Gint AQPF2 in wild soybean was significantly higher than that in cultivated soybean.These results suggested that AMF symbiosis could increase the accumulation of proline and the activity of CAT,improve the expression level of GintAQPF1 and GintAQPF2,and stimulate the growth of soybean roots,thus alleviate stress damage of drought stress on the plant.