UV-B stress reshapes root-associated microbial communities and networks, driven by host plant resistance

Elevated UV-B radiation, a growing threat to global crop production since the 1970s, impacts both plant physiology and their associated microbiomes. While the role of soil microbes in plant adaptation to abiotic stresses is well documented, the effects of aboveground UV-B radiation on root-associated microorganisms remain poorly understood. This study investigated how root microbial communities in UV-B-resistant and UV-B- sensitive highland barley varieties respond to UV-B stress, uncovering core microbial populations linked to plant resistance. We showed that UV-B stress induces compositional changes in root-associated prokaryotic communities but not fungal ones. Notably, UV-B stress increased microbial connectivity in the rhizosphere of sensitive plants while diminishing it within their root-associated networks. In contrast, resistant plants displayed an opposite pattern, suggesting sensitive plants 'ask for help' from rhizospheric microbes under stress, while resistant plants maintain robust endosphere microbial interactions. A keystone bacterial group, identified via forest model analysis, and affiliated with the genus Mesorhizobium, was significantly suppressed by UV-B stress in the rhizosphere of sensitive plants but remained stable in resistant ones. Inoculation with Mesorhizobium spp. enhanced plant growth and reduced oxidative stress in UV-B-sensitive barley seedlings, indicating its crucial role in UV-B tolerance. Our study highlights the importance of preserving specific microbial populations in the rhizosphere to bolster plant resilience against abiotic stressors.