Reduced root secretion of valine in Rosa-microbe interaction contributes to the decreased colonization of pathogenic Agrobacterium tumefaciens

Root exudates play a critical role in root-microbe interactions. Agrobacterium tumefaciens causes crown gall disease in multiple plant species, but the rose root exudates-mediated inhibition of Agrobacterium in the rhizosphere is poorly understood. In this study, the influence of preinoculation with beneficial bacteria or pathogens on root exudates and subsequent colonization by A. tumefaciens was investigated in a split-root system. We found that preinoculation of rose plants in a split-root system with Bacillus velezensis CLA178 or A. tumefaciens C58 inhibited the subsequent colonization by C58. The root secretion of valine had positive effects on the chemotaxis, biofilm formation, colonization of C58 and crown gall disease severity, but the secretion of valine decreased significantly when Rosa multiflora plants were preinoculated with CLA178 or C58. These results indicated that the rose plants reduced the root secretion of valine in response to microbial colonization, thereby reducing the colonization of Agrobacterium and disease severity. This study provides new insights into the root exudates-mediated interactions of rose plants, B. velezensis and A. tumefaciens, and proposes a potential way for controlling crown gall disease.

Keywords: Rosa; colonization; crown gall disease; root exudates; valine.