Coordination of root auxin with the fungus Piriformospora indica and bacterium Bacillus cereus enhances rice rhizosheath formation under soil drying

Moderate soil drying (MSD) is a promising agricultural technique that can reduce water consumption and enhance rhizosheath formation promoting drought resistance in plants. The endophytic fungus Piriformospora indica (P. indica) with high auxin production may be beneficial for rhizosheath formation. However, the integrated role of P. indica with native soil microbiome in rhizosheath formation is unclear. Here, we investigated the roles of P. indica and native bacteria on rice rhizosheath formation under MSD using high-throughput sequencing and rice mutants. Under MSD, rice rhizosheath formation was significantly increased by around 30% with P. indica inoculation. Auxins in rice roots and P. indica were responsible for the rhizosheath formation under MSD. Next, the abundance of the genus Bacillus, known as plant growth-promoting rhizobacteria, was enriched in the rice rhizosheath and root endosphere with P. indica inoculation under MSD. Moreover, the abundance of Bacillus cereus (B. cereus) with high auxin production was further increased by P. indica inoculation. After inoculation with both P. indica and B. cereus, rhizosheath formation in wild-type or auxin efflux carrier OsPIN2 complemented line rice was higher than that of the ospin2 mutant. Together, our results suggest that the interaction of the endophytic fungus P. indica with the native soil bacterium B. cereus favors rice rhizosheath formation by auxins modulation in rice and microbes under MSD. This finding reveals a cooperative contribution of P. indica and native microbiota in rice rhizosheath formation under moderate soil drying, which is important for improving water use in agriculture.