Fast induction of biosynthetic polysaccharide genes lpxA, lpxE, and rkpI of Rhizobium sp. strain PRF 81 by common bean seed exudates is indicative of a key role in symbiosis

• Published in: Functional & integrative genomics Vol. 13; no. 2; pp. 275 - 283
• Main Authors: Oliveira, Luciana Ruano, Rodrigues, Elisete Pains, Marcelino-Guimarães, Francismar Corrêa, Oliveira, André Luiz Martinez, Hungria, Mariangela
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-06-2013; Springer Nature B.V
• Subjects: Agrobacterium radiobacter; Animal Genetics and Genomics; Bacteria; Beans; Biochemistry; Bioinformatics; Biomedical and Life Sciences; Biosynthesis; Cell Biology; cell walls; chemical structure; gene expression regulation; Gene Expression Regulation, Bacterial - drug effects; genes; Genes, Bacterial - genetics; Genomics; Life Sciences; Microbial Genetics and Genomics; Nitrogen; Original Paper; Phaseolus - chemistry; Phaseolus vulgaris; Phylogeny; Plant Exudates - pharmacology; Plant Genetics and Genomics; polysaccharides; Polysaccharides, Bacterial - biosynthesis; Polysaccharides, Bacterial - genetics; quantitative polymerase chain reaction; reverse transcription; Rhizobium; Rhizobium - drug effects; Rhizobium - genetics; Rhizobium etli; Rhizobium leguminosarum; Rhizobium tropici; Seeds - chemistry; Sinorhizobium; Soils; Symbiosis; Symbiosis - drug effects; Symbiosis - genetics; Symbiosis; Biological nitrogen fixation; K-Antigen polysaccharide; RT-qPCR; LPS
• ISSN: 1438-793X; 1438-7948
• DOI: 10.1007/s10142-013-0322-7

Rhizobial surface polysaccharides (SPS) are, together with nodulation (Nod) factors, recognized as key molecules for establishment of rhizobia–legume symbiosis. In Rhizobium tropici, an important nitrogen-fixing symbiont of common bean (Phaseolus vulgaris L.), molecular structures and symbiotic roles of the SPS are poorly understood. In this study, Rhizobium sp. strain PRF 81 genes, belonging to the R. tropici group, were investigated: lpxA and lpxE, involved in biosynthesis and modification of the lipid-A anchor of lipopolysaccharide (LPS), and rkpI, involved in synthesis of a lipid carrier required for production of capsular polysaccharides (KPS). Reverse transcription quantitative PCR (RT-qPCR) analysis revealed, for the first time, that inducers released from common bean seeds strongly stimulated expression of all three SPS genes. When PRF 81 cells were grown for 48 h in the presence of seed exudates, twofold increases (p < 0.05) in the transcription levels of lpxE, lpxA, and rkpI genes were observed. However, higher increases (p < 0.05) in transcription rates, about 50-fold for lpxE and about 30-fold for lpxA and rkpI, were observed after only 5 min of incubation with common bean seed exudates. Evolutionary analyses revealed that lpxA and lpxE of PRF81 and of the type strain of R. tropici CIAT899ᵀclustered with orthologous Rhizobium radiobacter and were more related to R. etli and Rhizobium leguminosarum, while rkpI was closer to the Sinorhizobium sp. group. Upregulation of lpxE, lpxA, and rkpI genes suggests that seed exudates can modulate production of SPS of Rhizobium sp. PRF81, leading to cell wall changes necessary for symbiosis establishment.