Symbiotic induction of pyruvate dehydrogenase genes from Sinorhizobium meliloti

• Published in: Molecular plant-microbe interactions Vol. 13; no. 5; pp. 483 - 493
• Main Authors: CABANES, D, BOISTARD, P, BATUT, J
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01.05.2000; The American Phytopathological Society
• Subjects: Agronomy. Soil science and plant productions; Amino Acid Sequence; Base Sequence; Biological and medical sciences; DNA, Complementary; Economic plant physiology; Enzyme Induction; Fundamental and applied biological sciences. Psychology; Medicago sativa - microbiology; Molecular Sequence Data; Oxygen Consumption; Promoter Regions, Genetic; Pyruvate Dehydrogenase Complex - chemistry; Pyruvate Dehydrogenase Complex - genetics; Sequence Homology, Amino Acid; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - genetics; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Symbiosis; Rhizobium meliloti; Multienzyme complex; Nucleotide sequence; Enzyme; Induction; Operon; Medicago sativa; Pyruvate dehydrogenase (lipoamide); Vegetal microorganism relation; Homology; Gene organization; Gene expression; Leguminosae; Dicotyledones; Angiospermae; Bacteria; Spermatophyta; Oxidoreductases; Fodder crop; Rhizobiaceae; Aminoacid sequence
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/mpmi.2000.13.5.483

Genes coding for components of the pyruvate dehydrogenase (PDH) multienzyme complex (PDHc) from Sinorhizobium meliloti, the alfalfa symbiont, have been isolated on the basis of their high expression in symbiotic bacteria. The Elp component, PDH, is encoded by two genes, pdhAalpha (1,047 bp) and pdhAbeta (1,383 bp), a situation encountered in the alpha-proteobacteria Rickettsia prowazekii and Zymomonas mobilis as well as in some gram-positive bacteria and in mitochondria. pdhAalpha and pdhAbeta precede pdhB (1,344 bp), which encodes the E2p component, dihydrolipoamide acetyltransferase, of the PDHc. No gene encoding the E3 component, lipoamide dehydrogenase, was found in the immediate vicinity of pdhA and pdhB genes. pdhAalpha, pdhAbeta and pdhB likely constitute an operon. Here, we provide evidence that pdhA expression is induced in the symbiotic stage, compared with free-living conditions. We demonstrate that symbiotic expression of pdhA genes does not depend on the fix LJ regulatory cascade that regulates nitrogen fixation and respiration gene expression in symbiotic S. meliloti cells. Induction of pdhA expression could be obtained under free-living conditions upon the addition of pyruvate to the culture medium. Induction by pyruvate and symbiotic activation of pdh gene expression take place at the same promoter.