Cremers H C, Batley M, Redmond J W, Wijfjes A H, Lugtenberg B J, Wijffelman C A
Department of Plant Molecular Biology, Leiden University, The Netherlands.
J Biol Chem. 1991 May 25;266(15):9556-64.
The patterns of O-acetylation of the exopolysaccharide (EPS) from the Sym plasmid-cured derivatives of Rhizobium leguminosarum bv. trifolii strain LPR5, R. leguminosarum bv. trifolii strain ANU843 and R. leguminosarum bv. viciae strain 248 were determined by 1H and 13C NMR spectroscopy. Beside a site indicative of the chromosomal background, these strains have one site of O-acetylation in common, namely residue b of the repeating unit. The O-acetyl esterification pattern of EPS of the Sym plasmid-cured derivatives of strains LPR5, ANU843, and 248 was not altered by the introduction of a R. leguminosarum bv. viciae Sym plasmid or a R. leguminosarum bv. trifolii Sym plasmid. The induction of nod gene expression by growth of the bacteria in the presence of Vicia sativa plants or by the presence of the flavonoid naringenin, produced no significant changes in either amount or sites of O-acetyl substitution. Furthermore, no such changes were found in the EPS from a Rhizobium strain in which the nod genes are constitutively expressed. The substitution pattern of the exopolysaccharide from R. leguminosarum is, therefore, determined by the bacterial genome and is not influenced by genes present on the Sym plasmid. This conclusion is inconsistent with the suggestion of Philip-Hollingsworth et al. (Philip-Hollingsworth, S., Hollingsworth, R. I., Dazzo, F. B., Djordjevic, M. A., and Rolfe, B. G. (1989) J. Biol. Chem. 264, 5710-5714) that nod genes of R. leguminosarum bv. trifolii, by influencing the acetylation pattern of EPS, determine the host specificity of nodulation.
通过¹H和¹³C核磁共振光谱法测定了豆科根瘤菌三叶草生物变种LPR5菌株、豆科根瘤菌三叶草生物变种ANU843菌株以及豌豆根瘤菌蚕豆生物变种248菌株的共生质粒治愈衍生物胞外多糖（EPS）的O - 乙酰化模式。除了一个指示染色体背景的位点外，这些菌株有一个共同的O - 乙酰化位点，即重复单元的b残基。菌株LPR5、ANU843和248的共生质粒治愈衍生物的EPS的O - 乙酰酯化模式不会因引入豌豆根瘤菌蚕豆生物变种共生质粒或豆科根瘤菌三叶草生物变种共生质粒而改变。在蚕豆植株存在的情况下细菌生长或黄酮类化合物柚皮苷的存在诱导结瘤基因表达，O - 乙酰取代的量或位点均未发生显著变化。此外，在结瘤基因组成型表达的根瘤菌菌株的EPS中未发现此类变化。因此，豆科根瘤菌胞外多糖的取代模式由细菌基因组决定，不受共生质粒上基因的影响。这一结论与Philip - Hollingsworth等人（Philip - Hollingsworth, S., Hollingsworth, R. I., Dazzo, F. B., Djordjevic, M. A., and Rolfe, B. G. (1989) J. Biol. Chem. 264, 5710 - 5714）的观点不一致，他们认为豆科根瘤菌三叶草生物变种的结瘤基因通过影响EPS的乙酰化模式来决定结瘤的宿主特异性。
