Soybean seed lectin prevents the accumulation of S-adenosyl methionine synthetase and the S1 30S ribosomal protein in Bradyrhizobium japonicum under C and N starvation.

Soybean lectin (SBL) participates in the recognition between Bradyrhizobium japonicum and soybean although its role remains unknown. To search for changes in the proteome in response to SBL, B. japonicum USDA 110 was incubated for 12 h in a C- and N-free medium with or without SBL (10 μg ml(-1)), and the soluble protein profiles were compared. Two polypeptides, S-adenosyl-methionine synthetase (MetK) and the 30S ribosomal protein S1 (RpsA), were found only in the fractions from rhizobia incubated without SBL. Transcript levels of metK and rpsA were not correlated with polypeptide levels, indicating that there was regulation at translation. In support of this proposal, the 5' translation initiation-region of rpsA mRNA contained folding elements as those involved in regulation of its translation in other species. Disappearance of MetK and RpsA from the soluble protein fractions of SBL-treated rhizobia suggests that SBL might have attenuated the nutritional stress response of B. japonicum.