With the warming global climate, drought stress is considered to be the most important abiotic factor limiting plant growth and yield in the world. Drought stress has serious impacts on crop production. Many researchers have studied the influences of drought stress on crop production and plant physiology; however, few researchers have combined root exudates with root-associated microbiomes for their mutual effects under drought conditions. In this review, we systematically illustrate the impact of drought stress on root exudates and root-associated microbiomes, and then we discuss the mutual regulation of root-associated microbiomes and the host plant in helping the plant adapt to drought. Finally, we construct a framework for the mutual connections between the plant, root exudates, and the microbiome. We hope this review can provide some significant guidelines to promote the study of drought resistance in plants in association with the rhizosphere microbiota.

Asian cultivated rice (Oryza sativa L.), domesticated from Asian wild rice, is a staple food crop for populations around the world. Asian cultivated rice has undergone physiological changes in the process of its evolution from Asian wild rice, and the closely related rhizosphere microorganisms may have changed in the process of plant domestication. However, the rhizosphere microorganisms of different Asian wild rice species and their related indica and japonica cultivated rice have not yet been illustrated clearly. This study aimed to illustrate the microbial community structures in the rhizosphere of Asian wild rice (common wild rice, nivara wild rice, medicinal wild rice, and spotted wild rice) and Asian cultivated rice (indica and japonica accessions) through the high-throughput sequencing of 16S rDNA, ITS amplifiers and metagenomic data. The results showed that there were significant differences between wild and cultivated rice in their rhizosphere microbial community structures. In view of the indica and japonica rice, the bacterial and fungal community structures of indica rice with the nivara wild rice and medicinal wild rice were more similar than the japonica rice species. The indica and japonica rice had the lowest proportion of Actinobacteria than the wild rice species, and indica rice has the highest relative abundance of Nitrospira. As for the microbial functions, methane metabolism and pyruvate metabolism were found to be the common pathway enriched in the rhizosphere of common and nivara wild rice in comparison with the indica and japonica rice; in addition, though it was found that the relative abundances of the pathogenic fungi in the rhizosphere soil of indica and japonica rice were significantly lower than that of the wild rice, the relative abundances of Magnaporthales and Ustilaginales were significantly higher in indica and japonica rice than that of the wild rice. This study is expected to provide a theoretical basis for the development and utilization of rhizosphere microbial resources for wild and cultivated rice.

Wild rice is an important improved resource for cultivated rice and its unique ability to resist biotic and abiotic stress has attracted the attention of many scholars. The microbial community structure in the rhizosphere and leaf area of different rice varieties is also different, which may be one of the reasons for the difference in stress resistance between wild rice and cultivated rice. Forty-six bacteria were screened from the rhizosphere and phyllospheric of four different wild rice varieties. The results of functions of the screened strains showed that 18 strains had a good inhibitory effect on rice blast, and 33 strains had the ability to dissolve phosphorus, potassium, or fix nitrogen. Through potted experiment, the three bacterial strains, 499G2 (Peribacillus simplex), 499G3 (Bacillus velezensis), and 499G4 (B. megaterium) have a positive effect on the growth of cultivated rice in addition to the resistance to rice blast. The contents of total nitrogen, total phosphorus, total potassium, indole acetic acid (IAA), and chlorophyll in plant leaves were increased. In addition, in the verification test of rice blast infection, the application of inoculants can significantly reduce the content of malondialdehyde (MDA), increase the content of soluble sugar, and increase the activity of plant antioxidant enzymes, which may thereby improve rice in resisting to rice blast.