A beneficial bacterium influences myo -inositol homeostasis to protect plants during drought

Exposure to abiotic stress is one of the primary factors limiting crop productivity with drought stress is the most prevalent. Under drought, plants can produce osmolytes that increase water retention and prevent severe drought symptoms. Plant responses by extension also impact their associated root microbiomes through altered root metabolite concentrations and exudation. For example, myo-inositol (MI) serves as a precursor to osmolytes and also serves as a mediator for plant-microbe interactions in Arabidopsis thaliana (Arabidopsis). Here, we inoculated plants with Pantoea sp. R4 (R4), an isolate that can catabolize MI, and subjected them to drought. We observed that R4 colonized plants experiencing drought maintained their leaf relative water content while uninoculated planted did not, and that this colonization coincided with enrichment of MI in the shoots and depletion of MI in the roots. Interestingly, exogenous MI alone rescued water retention in wild-type Col-0, but not in int1 mutants, which lack the tonoplast MI transporter. Together, our results show that R4 colonization under drought conditions increases MI in the shoots, that this accumulation is associated with increased leaf water retention, and that INT1-mediated MI transport is required for this protection. Our results suggest that microbial colonization can alter how MI is localized in plants, which can inform future development of treatments to protect plants from drought.