Disease relevance of Rhizobitoxine

• Bradyrhizobium japonicum rhizobitoxine genes and putative enzyme functions: expression requires a translational frameshift [1].
• Some strains of Bradyrhizobium japonicum produce rhizobitoxine, a phytotoxin that causes foliar chlorosis on susceptible host plants [1].
• Rhizobitoxine is synthesized by the legume symbiont Bradyrhizobium elkanii and the plant pathogen Burkholderia andropogonis [2].
• The assay is based on the inhibition of Salmonella typhimurium beta-cystathionase by rhizobitoxine [3].
• Rhizobitoxine is a phytotoxin synthesized by some strains of the legume symbiont genus Bradyrhizobium and the plant pathogen Pseudomonas andropogonis [3].

High impact information on Rhizobitoxine

• The CBLAVG structure furthermore suggests a binding mode for rhizobitoxine and explains the failure of MVG to inhibit CBL [4].
• Bradyrhizobium elkanii rtxC gene is required for expression of symbiotic phenotypes in the final step of rhizobitoxine biosynthesis [5].
• In addition, complementation analysis of rtxC by cosmids differing in rtxC transcription levels suggested that rhizobitoxine production correlates with the amount of rtxC transcript [5].
• A large-deletion mutant of B. elkanii, USDA94 Delta rtx::Omega 1, which lacks rtxA, ORF1 (rtxC), ORF2, and ORF3, did not produce rhizobitoxine, dihydrorhizobitoxine, or serinol [6].
• The broad-host-range cosmid pLAFR1, which contains rtxA and these ORFs, complemented rhizobitoxine production in USDA94 Delta rtx::Omega 1 [6].

Biological context of Rhizobitoxine

• Thus, desaturation of dihydrorhizobitoxine by rtxC-encoded protein is essential for the bacterium to show rhizobitoxine phenotypes in planta [5].
• In light of results from DNA sequence comparison, gene disruption experiments, and dihydrorhizobitoxine production from various substrates, we discuss the biosynthetic pathway of rhizobitoxine and its evolutionary significance in bradyrhizobia [6].
• Rhizobitoxine did not cause cell death at a concentration sufficient to eliminate hydrogenase expression [7].
• We cloned and sequenced a cluster of genes involved in the biosynthesis of rhizobitoxine, a nodulation enhancer produced by Bradyrhizobium elkanii [6].
• Further complementation experiments involving cosmid derivatives obtained by random mutagenesis with a kanamycin cassette revealed that at least rtxA and rtxC are necessary for rhizobitoxine production [6].

Associations of Rhizobitoxine with other chemical compounds

• However, recent studies have revealed that rhizobitoxine plays a positive role in establishing symbiosis between B. elkanii and host legumes: rhizobitoxine enhances the nodulation process by inhibiting ACC (1-aminocyclopropane-1-carboxylate) synthase in the ethylene biosynthesis of host roots [8].

Gene context of Rhizobitoxine

• New assay for rhizobitoxine based on inhibition of 1-aminocyclopropane-1-carboxylate synthase [2].
• By using these mutants, it was found that rhizobitoxine plays no apparent role in the nodulation of rj1 soybeans [9].

References