Department of Chemical Sciences, University of Napoli, Via Cintia 4, 80126, Napoli, Italy.
Institute for Research on Combustion (IRC), CNR, Naples (Italy), Piazzale Vincenzo Tecchio 80, 80126, Napoli, Italy.
Angew Chem Int Ed Engl. 2020 Apr 16;59(16):6368-6374. doi: 10.1002/anie.201914053. Epub 2020 Mar 10.
The lipopolysaccharide (LPS) O-antigen structure of the plant pathogen Rhizobium radiobacter strain TT9 and its possible role in a plant-microbe interaction was investigated. The analyses disclosed the presence of two O-antigens, named Poly1 and Poly2. The repetitive unit of Poly2 constitutes a 4-α-l-rhamnose linked to a 3-α-d-fucose residue. Surprisingly, Poly1 turned out to be a novel type of biopolymer in which the repeating unit is formed by a monosaccharide and an amino-acid derivative, so that the polymer has alternating glycosidic and amidic bonds joining the two units: 4-amino-4-deoxy-3-O-methyl-d-fucose and (2'R,3'R,4'S)-N-methyl-3',4'-dihydroxy-3'-methyl-5'-oxoproline). Differently from the O-antigens of LPSs from other pathogenic Gram-negative bacteria, these two O-antigens do not activate the oxidative burst, an early innate immune response in the model plant Arabidopsis thaliana, explaining at least in part the ability of this R. radiobacter strain to avoid host defenses during a plant infection process.
我们研究了植物病原菌根瘤菌菌株 TT9 的脂多糖（LPS）O-抗原结构及其在植物-微生物相互作用中的可能作用。分析表明存在两种 O-抗原，分别命名为 Poly1 和 Poly2。Poly2 的重复单元由 4-α-l-鼠李糖连接到 3-α-d-岩藻糖残基组成。令人惊讶的是，Poly1 原来是一种新型的生物聚合物，其重复单元由单糖和氨基酸衍生物形成，因此聚合物具有交替的糖苷和酰胺键连接两个单元：4-氨基-4-去氧-3-O-甲基-d-岩藻糖和（2'R，3'R，4'S）-N-甲基-3'，4'-二羟基-3'-甲基-5'-氧代脯氨酸）。与来自其他致病性革兰氏阴性细菌的 LPS 的 O-抗原不同，这两种 O-抗原不能激活模型植物拟南芥中的早期先天免疫反应氧化爆发，这至少部分解释了这种根瘤菌菌株在植物感染过程中逃避宿主防御的能力。
