The eff-482 locus of Sinorhizobium meliloti CXM1-105 that influences symbiotic effectiveness consists of three genes encoding an endoglycanase, a transcriptional regulator and an adenylate cyclase

Abstract

The mutant T482 of Sinorhizobium meliloti CXM1-105, which carries a Tn5 insertion on megaplasmid 1, exhibits an enhanced symbiotic efficiency phenotype. Three genes, eglC, cya3 and syrB2, were identified in the eff-482 region tagged by the Tn5 insertion in T482. The eglC gene encodes an endoglycanase which contributes to the depolymerization of the exo-polysaccharide succinoglycan. The N-terminal region of the predicted cya3 gene product was similar to eukaryotic-type adenylate cyclases from Brevibacterium liquefaciens and Streptomyces coelicolor. Four contiguous tetratricopeptide repeats which are known to mediate protein-protein interactions were identified in the C-terminal portion of Cya3. Complementation analysis demonstrated that cya3 indeed encodes a functional adenylate cyclase. A central helix-turn-helix DNA-binding motif and a putative C-terminal coiled-coil structure implicated in protein oligomerization were found in SyrB2. Extra copies of the syrB2 gene negatively affect transcription of both syrB2 itself and cya3. The Tn5 insertion in T482 was localized between the divergently transcribed genes eglC and syrB2. It eliminated eglC function and slightly stimulated transcription of both syrB2 and cya3, which lies downstream of syrB2. Mutants carrying insertions of the lacZ-Gm interposon in the genes eglC, syrB2 and cya3 exhibit the same phenotype as mutant T482, indicating that these three genes influence symbiotic efficiency.

The LuxR Homolog ExpR, in Combination with the Sin Quorum Sensing System, Plays a Central Role in Sinorhizobium meliloti Gene Expression

“…The present study is the first to suggest a role for quorum sensing in the production of LMW succinoglycan. The endoglycanases ExsH and EglC, both of which play a role in the synthesis of the LMW fraction of succinoglycan required for the successful invasion of the plant host (49,66), seem to be controlled by quorum sensing. We have confirmed that indeed, the exsH gene is expressed at a higher level in the presence of the ExpR regulator and an active Sin system (see Table 5).…”

“…Image acquisition and data analysis were performed as described previously (4,49). In brief, mean signal and mean local background intensities were obtained for each spot of the microarray images by using the ImaGene 5.0 software for spot detection, image segmentation, and signal quantification (Biodiscovery, Inc., Los Angeles, Calif.).…”

Nucleotide sequence and predicted functions of the entire Sinorhizobium meliloti pSymA megaplasmid

“…13), a functional copy of the groESL chaperonin operon (14), and genes needed for catabolism of betaines (15). However, except for syrB and a locus that inf luences symbiotic effectiveness (16), little was known outside this 275-kb region. Recently, an alcohol dehydrogenase (adhA; ref.…”

Simulation of legume-rhizobia symbiosis evolution under the multi-strain competition of bacteria for inoculation of symbiotic habitats

“…Выявление генов обеих групп представляет большой интерес для конструирования хозяйственноценных штаммов ризобий, которое может быть связано как с усилением активности генов первой категории, так и с элиминацией генов второй категории. Генетичес-кие модификации обоих типов описаны в литературе (Bosworth et al, 1992;Sharypova et al, 1998), одна-ко, как показала наша работа, они смогут обеспечить существенное возрастание эффективности симбиоза только в сочетании с оптимизацией общей структуры микробно-растительной системы, обеспечивающей высокие частоты N 2 -фиксирующих штаммов в клу-беньках растений.…”