Nitrogen fixation by native Bradyrhizobia in symbiosis with Lupinus mariae-josephae requires a T3SS encoding a NopE-like effector

Several bradyrhizobial isolates from L. mariae-josephae root nodules [1] contain a type III secretion system (T3SS) within a cluster of about 30 genes. Among those genes, ttsI codes for the transcriptional activator of the system. Mutation of ttsI resulted in the formation of white, non-fixing nodules with the natural legume host, L. mariae-josephae. The T3SS cluster also contains a gene coding for a NopE-like protein. NopE proteins have been demonstrated to be effectors in the Bradyrhizobium-soybean symbiosis [2] and belong to a small group of poorly characterized proteins from plant-associated bacteria that contain one or two autocleavage motifs known as DUF1521 (Schirrmeister et al. 2011). The amino acid sequence of a NopE-like protein in the L. mariae-josephae strain LmjC contains just one autocatalytic motif. This is unlike NopE1 and NopE2 proteins secreted by the T3SS of B. japonicum, that contain two motifs [3]. The autocleavage of LmjC NopE protein was analyzed after expression in E. coli and purification. Two protein fragments of the predicted sizes appeared in the presence of Ca2+, Cu2+, Cd2+, Zn2+ and Mn2+ cations. In contrast, autocleavage did not take place in the presence of Ni2+, Co2+ or Mg2+. Site-directed mutagenesis of the DUF1521 motif in LmjC NopE abolished self-cleavage in vitro. Symbiotic competence of a NopE- mutant with the L. mariae-josephae host was not affected. Possible roles of NopE are discussed.

Quorum Sensing is essential for an effective symbiosis in R. leguminosarum UPM791.

The implications of Quorum Sensing in the establishment of a successful symbiosis of Rhizobium leguminosarum bv. viciae (Rlv) with legume plants are discussed in this work. In order to analyze the significance and regulation of the production of AHL signal molecules, mutants deficient in each of the two QS systems present in Rlv UPM791 were constructed. A detailed analysis of the effect of these mutations on growth, AHL production, biofilm formation and symbiosis with pea, vetch and lentil plants has been carried out.

Native bradyrhizobia isolated from Lupinus mariae-josephae possess an essential T3SS for symbiosis

Analysis of the genome sequence of bradyrhizobia strains isolated from root nodules of Lupinus mariae-josephae revealed the presence of a type III secretion system (T3SS). Mutagenesis of ttsI gene that codes for the transcriptional activator (TtsI) resulted in the formation of white, non-fixing nodules in L. mariae-josephae. The T3SS cluster includes a gene coding for a NopE-like protein with an autocleavage motif. The NopE protein is an effector in the Bradyrhizobium-soybean symbiosis (Wenzel et al., 2010). The autocatalytic properties of the purified NopE-like protein have been studied.

Metal Transport in the Rhizobium-Legume Symbiosis

Metal Transport in the Rhizobium-legume Symbiosis