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In the fibers of many plant species after the formation of secondary cell walls, cellulose-enriched cell wall layers (often named G-layers or tertiary cell walls) are deposited which are important in many physiological situations. Flax (Linum usitatissimum L.) phloem fibers constitutively develop tertiary cell walls during normal plant growth. During the gravitropic response after plant inclination, the deposition of a cellulose-enriched cell wall layer is induced in xylem fibers on one side of the stem, providing a system similar to that of tension wood in angiosperm trees. Atomic force microscopy (AFM), immunochemistry, and transcriptomic analyses demonstrated that the G-layer induced in flax xylem fibers was similar to the constitutively formed tertiary cell wall of bast (phloem) fibers but different from the secondary cell wall. The tertiary cell walls, independent of tissue of origin and inducibility, were twice as stiff as the secondary cell walls. In the gravitropic response, the tertiary cell wall deposition rate in xylem was higher than that of the secondary cell wall. Rhamnogalacturonan I (RG-I) with galactan side chains was a prominent component in cellulose-rich layers of both phloem and xylem flax fibers. Transcriptomic events underlying G-layer deposition in phloem and xylem fibers had much in common. At the induction of tertiary cell wall deposition, several genes for rhamnosyltransferases of the GT106 family were activated in xylem samples. The same genes were expressed in the isolated phloem fibers depositing the tertiary cell wall. The comparison of transcriptomes in fibers with both inducible and constitutive tertiary cell wall deposition and xylem tissues that formed the secondary cell walls is an effective system that revealed important molecular players involved in the formation of cellulose-enriched cell walls. [ABSTRACT FROM AUTHOR]

We previously discovered that Pseudomonas chlororaphis NRRL B-30761 produces monorhamnolipids (RLs) with predominantly 3-hydroxydodecenoyl-3-hydroxydecanoate (C-C) or 3-hydroxydodecanoyl-3-hydroxydecanoate (C-C) as the lipid moiety under static growth conditions only. We have now cloned, sequenced, and analyzed in silico the gene locus of NRRL B-30761 containing the putative coding sequences of rhamnosyltransferase chain A ( rhlA, 894 bps), rhamnosyltransferase chain B ( rhlB, 1272 bps), and N-acyl-homoserine lactone-dependent transcriptional regulatory protein ( rhlR, 726 bps). The putative gene products RhlA (297 amino acid residues or a.a.), RhlB (423 a.a.), and RhlR (241 a.a.) only have between 60 and 65 % a.a. identities to their respective closest matched homologs in P. aeruginosa. Polymerase chain reaction (PCR)-based assay did not detect the presence of rhamnosyltransferase C gene ( rhlC) in P. chlororaphis, suggesting a genetic basis for the lack of dirhamnose-lipid (RL) synthesis in this organism. We thus genetically constructed an RL-synthesizing P. chlororaphis by expressing a rhamnosyltransferase C ( rhlC) gene of P. aeruginosa using an expression vector (pBS29-P2- gfp) containing a Pseudomonas syringae promoter. The RL/RL ratio is 2.4 in the rhamnolipid (RL) sample isolated from the genetically engineered (GE) P. chlororaphis [pBS29-P2- rhlC], in contrast to undetectable RL in the GE P. chlororaphis [pBS29-P2- gfp] control cells based on LC-MS analysis. The critical micelle concentrations of the RL and RL samples from GE P. chlororaphis [pBS29-P2- rhlC] and the control [pBS29-P2- gfp] cells were ca. 0.1 mM, and their minimum surface tensions were ca. 26 mN/m with no significant difference. [ABSTRACT FROM AUTHOR]

The β1,2-rhamnosyltransferase WsaF is involved in the biosynthesis of a polyrhamnan chain which is attached to the surface-layer protein from Geobacillus stearothermophilus NRS 2004/3a. The enzyme belongs to the large retaining GT4 family. To date, no structure of a rhamnosyltransferase has been published. Recombinant purified native WsaF has been crystallized, resulting in crystals that belonged to space group P212121 with unit-cell parameters a = 50.5, b = 56.1, c = 276.8 Å and diffracted to 3.0 Å resolution. Selenomethionine-variant WsaF crystallized in space group P21 with unit-cell parameters a = 75.9, b = 75.5, c = 78.1 Å and diffracted to 2.3 Å resolution. [ABSTRACT FROM AUTHOR]