Differential response of the plant Medicago truncatula to its symbiont Sinorhizobium meliloti or an exopolysaccharide-deficient mutant

Abstract

Sinorhizobium meliloti forms symbiotic, nitrogen-fixing nodules on the roots of Medicago truncatula. The bacteria invade and colonize the roots through structures called infection threads. S. meliloti unable to produce the exopolysaccharide succinoglycan are unable to establish a symbiosis because they are defective in initiating the production of infection threads and in invading the plant. Here, we use microarrays representing 16,000 M. truncatula genes to compare the differential transcriptional responses of this host plant to wild-type and succinoglycan-deficient S. meliloti at the early time point of 3 days postinoculation. This report describes an early divergence in global plant gene expression responses caused by a rhizobial defect in succinoglycan production, rather than in Nod factor production. The microarray data show that M. truncatula inoculated with wild-type, succinoglycan-producing S. meliloti more strongly express genes encoding translation components, protein degradation machinery, and some nodulins than plants inoculated with succinoglycan-deficient bacteria. This finding is consistent with wild-type-inoculated plants having received a signal, distinct from the well characterized Nod factor, to alter their metabolic activity and prepare for invasion. In contrast, M. truncatula inoculated with succinoglycan-deficient S. meliloti more strongly express an unexpectedly large number of genes in two categories: plant defense responses and unknown functions. One model consistent with our results is that appropriate symbiotically active exopolysaccharides act as signals to plant hosts to initiate infection thread formation and that, in the absence of this signal, plants terminate the infection process, perhaps via a defense response.nitrogen fixation ͉ nodule ͉ succinoglycan ͉ microarray ͉ legume

Potential Emergence of Multi-quorum Sensing Inhibitor Resistant (MQSIR) Bacteria

“…For nodulation efficiency, RhiI synthesized C6HSL, C7HSL and C8-HSL activate the rhiABC genes. These QSS also govern motility and exopolysaccharide production which is required for infection process, and biofilm formation [80,81]. In Sinorhizobium meliloti, sinI/ sinR and expR, regulate the Sin QSS through long chain AHLs: C12HSL to C18HSL [29,[82][83][84].…”

Immunosuppression duringRhizobium-legume symbiosis

“…The transcriptomic data showed that S.meliloti exoY minus mutant (not synthesize succinoglycan) induced the elevated expression of many defense related genes on host M. truncatula, suggesting that succinoglycan suppresses host immunity during infection. 17 Whether the oligomer of EPS is perceived by a receptor, interacting with MAPKs to constitute a signaling pathway will be elucidated by forward genetics and biochemistry.…”

How legumes recognize rhizobia

“…Of particular interest are studies that used mutant strains of rhizobia to dissect the transcriptional changes associated to recognition of signal molecules from bacteria. 28,[30][31][32][33] (Table 1). Jones and collaborators 32 showed the differences in the M. truncatula transcriptional response when it was inoculated with the wild type strain or a succinoglycan-deficient strain of S. meliloti unable to establish a successful infection.…”

“…28,[30][31][32][33] (Table 1). Jones and collaborators 32 showed the differences in the M. truncatula transcriptional response when it was inoculated with the wild type strain or a succinoglycan-deficient strain of S. meliloti unable to establish a successful infection. The absence of this exopolysaccharide resulted in a reduction of genes involved in protein synthesis and degradation, as well as genes involved in nodulation (known as nodulins).…”