Signal quenching, detoxification and mineralization of vir gene‐inducing phenolics by the VirH2 protein of Agrobacterium tumefaciens

Abstract

SummaryPlant tumorigenesis by Agrobacterium tumefaciens requires approximately 20 Vir proteins, transcription of which is induced by a family of phenolic compounds released from plant wound sites. One Vir protein, VirH2, plays a role in the metabolism of at least one phenolic inducer inasmuch as it converts ferulic acid, a potent vir gene inducer, to the non-inducer caffeate by O-demethylation of a methoxyl group. Here, we tested VirH2-dependent O-demethylation of 16 other vir -inducing phenolics, and detected this activity for each compound. However, O-demethylation rates differed enormously, with the strongest vir gene inducers such as acetosyringone being demethylated extremely slowly. Compounds containing two methoxyl groups were demethylated at both positions. In general, phenolic inducers were more toxic than their demethylated counterparts. A virH2 mutant was more sensitive than the wild type to growth inhibition by virtually all phenolic inducers tested, indicating that VirH2 detoxifies these compounds. VirH2 also played a role in mineralization of some phenolics. It converted vanillate to protocatechuate, which was then mineralized via the b b b b -ketoadipate pathway. Vanillyl alcohol and vanillin were also mineralized after being oxidized to vanillate. All three compounds served as sole sources of carbon, whereas the remaining 13 compounds did not.

Nocturnal Production of Endospores in Natural Populations ofEpulopiscium-Like Surgeonfish Symbionts

“…The major product peak, m/e ϭ 296, corresponds to the parent compound minus one methyl group. The peak of m/e ϭ 73 corresponds to the trimethylsilyl ion, which is characteristic of trimethylsilylated compounds (9). The peak of m/e ϭ 147 represents a fragmentation product that we could not ascertain.…”

“…A 0.2 l aliquot of the sample was analyzed with gas chromatography/mass spectroscopy (GC/MS) as described previously (9). Purified DPA (Acros Organics, New Jersey) was used as a standard.…”

Transcriptome Profiling and Functional Analysis ofAgrobacterium tumefaciensReveals a General Conserved Response to Acidic Conditions (pH 5.5) and a Complex Acid-Mediated Signaling Involved inAgrobacterium-Plant Interactions

“…Why virE0 and virE1 are acid inducible is not clear, especially since neither virE2 nor virE3 is acid inducible. VirH1 and VirH2 share high homologies with cytochrome P-450 monooxygenases (9). Both genes are under the control of VirA-VirG, but mutations in either one or both have no significant effect on virulence, as determined by laboratory assays (9).…”

“…VirH1 and VirH2 share high homologies with cytochrome P-450 monooxygenases (9). Both genes are under the control of VirA-VirG, but mutations in either one or both have no significant effect on virulence, as determined by laboratory assays (9). In addition, the VirH2 protein can demethylate and mineralize many phenolic vir gene inducers and thereby reduce their toxic activity against bacterial growth and destroy their vir gene-inducing activity (9).…”

“…Both genes are under the control of VirA-VirG, but mutations in either one or both have no significant effect on virulence, as determined by laboratory assays (9). In addition, the VirH2 protein can demethylate and mineralize many phenolic vir gene inducers and thereby reduce their toxic activity against bacterial growth and destroy their vir gene-inducing activity (9). The fact that acid alone induces expression of both virH1 (Atu6150) and virH2 (Atu6151) suggests that many phenolic compounds are exuded by the plant and that it behooves Agrobacterium to detoxify these compounds.…”