Abstract
Mesorhizobium loti
MAFF303099 has a functional type III secretion system (T3SS) that is involved in the determination of nodulation competitiveness on Lotus. The
M. loti
T3SS cluster contains gene
y4yS
(
mlr8765
) that codes for a protein of unknown function (Y4yS). A mutation in the
y4yS
gene favors the
M. loti
symbiotic competitive ability on
Lotus tenuis
cv. Esmeralda and affects negatively the secretion of proteins through T3SS. Here we localize Y4yS in the bacterial membrane using a translational reporter peptide fusion.
In silico
analysis indicated that this protein presents a tetratricopeptide repeat (TPR) domain, a signal peptide and a canonical lipobox LGCC in the N-terminal sequence. These features that are shared with proteins required for the formation of the secretin complex in type IV secretion systems and in the Tad system, together with its localization, suggest that the
y4yS
-encoded protein is required for the formation of the
M
.
loti
T3SS secretin (RhcC2) complex. Remarkably, analysis of RhcC2 in the wild-type and
M. loti y4yS
mutant strains indicated that the absence of Y4yS affects negatively the accumulation of normal levels of RhcC2 in the membrane.