Rhizosphere microbes enhance plant resistance to cadmium through a root ROS-microbial IAA-root DNA methylation interkingdom signaling pathway

Plants deploy a "cry-for-help" strategy to recruit beneficial microbes, thereby enhancing stress resistance and expanding their ecological niches in harsh environments. However, the molecular mechanisms driving this plant-microbe communication remain poorly understood. To uncover the underlying dialogue, we explore interactions between two plant-growth-promoting bacteria (PGPBs) and their host plants, rice and Solanum nigrum, under heavy metal (HM) stress. We identify an interkingdom signaling pathway, characterized by "root reactive oxygen species (ROS)-microbial indole-3-acetic acid (IAA)-root DNA methylation," which mediates plant-PGPB interactions. Under HM stress, root-derived ROS triggers IAA synthesis in PGPBs, which subsequently suppresses ROS production in the roots, thereby mitigating HM damage in plants. Furthermore, PGPB-derived IAA induces root DNA methylation modifications via ROS-dependent pathways, establishing a cross-kingdom signaling mechanism that links microbial metabolism to plant DNA methylation. This interkingdom signaling pathway is widely observed in the rhizosphere, providing insights into plant-microbe interactions in adverse environments.