A putative 3‐hydroxyisobutyryl‐CoA hydrolase is required for efficient symbiotic nitrogen fixation in Sinorhizobium meliloti and Sinorhizobium fredii NGR234 Journal Articles uri icon

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abstract

  • SummaryWe report that the smb20752 gene of the alfalfa symbiont Sinorhizobium meliloti is a novel symbiotic gene required for full N2‐fixation. Deletion of smb20752 resulted in lower nitrogenase activity and smaller nodules without impacting overall nodule morphology. Orthologs of smb20752 were present in all alpha and beta rhizobia, including the ngr_b20860 gene of Sinorhizobium fredii NGR234. A ngr_b20860 mutant formed Fix− determinate nodules that developed normally to a late stage of the symbiosis on the host plants Macroptilium atropurpureum and Vigna unguiculata. However an early symbiotic defect was evident during symbiosis with Leucaena leucocephala, producing Fix− indeterminate nodules. The smb20752 and ngr_b20860 genes encode putative 3‐hydroxyisobutyryl‐CoA (HIB‐CoA) hydrolases. HIB‐CoA hydrolases are required for l‐valine catabolism and appear to prevent the accumulation of toxic metabolic intermediates, particularly methacrylyl‐CoA. Evidence presented here and elsewhere (Curson et al., , PLoS ONE 9:e97660) demonstrated that Smb20752 and NGR_b20860 can also prevent metabolic toxicity, are required for l‐valine metabolism, and play an undefined role in 3‐hydroxybutyrate catabolism. We present evidence that the symbiotic defect of the HIB‐CoA hydrolase mutants is independent of the inability to catabolize l‐valine and suggest it relates to the toxicity resulting from metabolism of other compounds possibly related to 3‐hydroxybutyric acid.

publication date

  • January 2017