Viral and chloroplastic signals essential for initiation and efficiency of translation in Agrobacterium tumefaciens

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 rose root exudate-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 subsequent colonization by C58. Root secretion of valine had positive effects on the chemotaxis, biofilm formation, colonization of C58, and crown gall disease severity, but valine secretion decreased significantly when Rosa multiflora plants were preinoculated with CLA178 or C58. These results indicated that rose plants reduced root secretion of valine in response to microbial colonization, thereby reducing the colonization of Agrobacterium colonization and disease severity. This study provides new insights into the root exudate-mediated interactions of rose plants, B. velezensis, and A. tumefaciens and proposes a potential way to control crown gall disease.

Identifying a Molecular Mechanism That Imparts Species-Specific Toxicity to YoeB Toxins

The ribosome-dependent E. coli (Ec) mRNase toxin YoeB has been demonstrated to protect cells during thermal stress. Agrobacterium tumefaciens (At), a plant pathogen, also encodes a YoeB toxin. Initial studies indicated that AtYoeB does not impact the growth of Ec, but its expression is toxic to the native host At. The current work examines this species-specific effect. We establish the highly similar structure and function of Ec and AtYoeB toxins, including the ability of the AtYoeB toxin to inhibit Ec ribosomes in vitro. Comparison of YoeB sequences and structures highlights a four-residue helix between β-strands 2 and 3 that interacts with mRNA bases within the ribosome. This helix sequence is varied among YoeB toxins, and this variation correlates with bacterial classes of proteobacteria. When the four amino acid sequence of this helix is transplanted from EcYoeB onto AtYoeB, the resulting chimera gains toxicity to Ec cells and lessens toxicity to At cells. The reverse is also true, such that EcYoeB with the AtYoeB helix sequence is less toxic to Ec and gains toxicity to At cultures. We suggest this helix sequence directs mRNA sequence-specific degradation, which varies among proteobacterial classes, and thus controls growth inhibition and YoeB toxicity.