Herbaspirillum seropedicae rfbB and rfbC genes are required for maize colonization

Abstract

SummaryIn this study we disrupted two Herbaspirillum seropedicae genes, rfbB and rfbC, responsible for rhamnose biosynthesis and its incoporation into LPS. GC-MS analysis of the H. seropedicae wild-type strain LPS oligosaccharide chain showed that rhamnose, glucose and N-acetyl glucosamine are the predominant monosaccharides, whereas rhamnose and N-acetyl glucosamine were not found in the rfbB and rfbC strains. The electrophoretic pattern of the mutants LPS was drastically altered when compared with the wild type. Knockout of rfbB or rfbC increased the sensitivity towards SDS, polymyxin B sulfate and salicylic acid. The mutants attachment capacity to maize root surface plantlets was 100-fold lower than the wild type. Interestingly, the wild-type capacity to attach to maize roots was reduced to a level similar to that of the mutants when the assay was performed in the presence of isolated wild-type LPS, glucosamine or N-acetyl glucosamine. The mutant strains were also significantly less efficient in endophytic colonization of maize. Expression analysis indicated that the rfbB gene is upregulated by naringenin, apigenin and CaCl 2. Together, the results suggest that intact LPS is required for H. seropedicae attachment to maize root and internal colonization of plant tissues.

Transcriptional Analysis of <i>Pseudomonas stutzeri</i> A1501 Associated with Host Rice

“…In a Tn5 mutant of A. brasilense affected in the biosynthesis ofd TDP-rhamnose, LPS composition was modified and resulted in impaired attachment of the mutant to maize roots and reduced root colonization [29]. Additional studies recently were undertaken on H. serepedicae by Balsanelli et al [30] confirmed these data. In addition to LPS, a major outer membraneprotein from A. brasilense strain Cd was purified and shown, by in vitro adhesion assays, to bind to roots of wheat, corn and sorghum seedlings [31].…”

Naringenin Regulates Expression of Genes Involved in Cell Wall Synthesis inHerbaspirillum seropedicae

“…1B). Previously, Balsanelli et al (3) showed that strains unable to synthesize LPS were severely impaired in maize colonization. These authors also showed that the rmlB gene, whose product is involved in LPS biosynthesis, was upregulated by naringenin (4-fold), in agreement with our results showing that naringenin can modulate genes involved in the biosynthesis and modification of LPS.…”

“…To check whether any of the mutations influenced the colonization of maize (Zea mays), the protocol of Balsanelli et al (3) was used to test bacterial cell adhesion to root surface and internal colonization. No difference was observed between the parental strain (SmR1) and mutants in growth and root surface attachment (data not shown).…”

Potential of Bacterial Endophytes as Plant Growth Promoting Factors

“…Mutational analyses suggest that surface characteristics of bacteria play an important role in the establishment of endophytes in roots. The lipopolysaccharide composition, particularly the rhamnose content had an impact on attachment to and endophytic colonization of maize roots by H. seropedicae [30]. In a study conducted on rice plant it was found that exopolysaccharide production is necessary for plant colonization by the nitrogen-Fixing endophyte Gluconacetobacter diazotrophicus [31].…”