Succinoglycan production and nodulation of Medicago sativa roots are influenced by the activity of a novel tyrosine phosphatase of Sinorhizobium meliloti.

MEDEOT D; RIVERO MR; FERRARI W; ROSSI F; LIAUDAT JP; FISCHER S; BECKER A; JOFRE E

La Falda, Córdoba

Workshop; II Workshop Latinoamericano sobre Rizobacterias Promotoras del Desarrollo Vegetal; 2014

Many cell to cell interactions involve specific signal transduction pathways that are triggered by posttranslational modification of proteins such as phosphorylation. In E. coli, Wzc is a tyrosine autokinase essential for the assembly of the capsule. Wzc is dephosphorylated by Wzb, a low molecular weight phosphotyrosine phosphatase (LMW-PTP). Homologs of Wzc participate in the production of exopolysaccharides (EPS) in a variety of bacteria. Phosphorylation states of the tyrosines are also involved in biofilm formation and community development. In S. melilotiMedicago sativa symbiosis the production of the succinoglycan (EPS I) is essential for invasion and development of Medicago sativa root nodules. EPS are also significant virulence determinants for many plant and animal pathogens. In the present work, we demonstrated that a mutation in the SMc02309 gene, encoding a novel LMW-PTP of S. meliloti, altered the EPS production and the symbiotic performance with M. sativa plants. The potential role of SMc02309 gene in EPS I production and symbiosis with M. sativa was tested with a mutant strain Rm42 generated by a targeted insertion of an integrative plasmid. EPS I production was measured in 6- and 9-days-old culture supernatants from GMS medium supplemented with 240 mM NaCl. To analyze whether the SMc02309 protein influences the molecular weight distribution of EPS I, culture supernatants containing the succinoglycan were subjected to gel permeation chromatography. S. meliloti strains were assayed for their symbiotic phenotypes on M. sativa. Nodule formation was monitored each four days during four weeks. Rm42 evidenced a reduced amount of EPS I in 6-day-old culture supernatants compared to the wild-type strain, Rm2011. As expected, the mutant strain Rm42 complemented with the wild type allele regained the EPS levels found in Rm2011. To confirm that the hexose equivalents measured were derived from EPS I, the S. meliloti exoY mutant deficient in production of EPS I was included as control. High molecular weight (HMW EPS I) and low molecular weight (LMW EPS I) EPS I have been described. Rm2011 produced HMW and LMW EPS I at a ratio of 76:24, whereas this ratio in the mutant strain Rm42 (at 69:31) was slightly modified in favor of the LMW-EPS I. Because EPS I plays an essential role in nodule invasion, the symbiotic proficiency of mutant strain Rm42 was compared with that of the wild-type strain Rm 2011. Although both strains established an effective symbiosis, as evidenced by the presence of pink and elongated nodules; the mutant strain Rm42 exhibited a delay in the nodulation of the M. sativa roots. The evidence implicating the influence of SMc02309 activity in EPS I production and nodulation of M. sativa roots, though preliminary, is promising. Protein phosphorylation on tyrosine has emerged as a key device in the control of numerous cellular functions in bacteria. Further studies will be required,however, to reveal whether or not SMc02309 provides crosstalk with other signaling pathways.