Department of Plant Pathology, Cornell University, Ithaca, New York 14853-5908.
Appl Environ Microbiol. 1993 Jun;59(6):1756-61. doi: 10.1128/aem.59.6.1756-1761.1993.
The enterobacterium Erwinia chrysanthemi causes soft-rot diseases involving extensive tissue maceration in a wide variety of plants and secretes multiple pectic enzymes that degrade plant cell walls and middle lamellae. An E. chrysanthemi mutant with directed deletions or insertions in genes pehX, pelX, pelA, pelB, pelC, and pelE, which encode exo-poly-alpha-d-galacturonosidase, exopolygalacturonate lyase, and four isozymes of pectate lyase, respectively, was constructed by the marker exchange of a cloned pehX::TnphoA fragment into E. chrysanthemi CUCPB5010, a Delta(pelA pelE) Delta(pelB pelC)::28bp Delta(pelX)Delta4bp derivative of strain EC16. This mutant, E. chrysanthemi CUCPB5012, no longer caused pitting in a standard pectate semisolid agar medium used to detect pectolytic activity in bacteria. Nevertheless, the mutant still macerated leaves of chrysanthemum (Chrysanthemum morifolium), although with reduced virulence. The mutant was found to produce significant pectate lyase activity in rotting chrysanthemum tissue and in minimal media containing chrysanthemum extracts or cell walls as the sole carbon source. Activity-stained, ultra-thin-layer isoelectric focusing gels revealed the presence in these preparations of several pectate lyase isozymes with pIs ranging from highly acidic to highly alkaline. Sterile culture fluids containing these isozymes were able to macerate chrysanthemum leaf tissue. Unlike the products of the pelA, pelB, pelC, and pelE genes in E. chrysanthemi EC16, these plant-inducible pectate lyase isozymes were not produced in minimal medium containing pectate. The results suggest that E. chrysanthemi produces two sets of independently regulated pectate lyase isozymes that are capable of macerating plant tissues.
肠杆菌欧文氏菌引起多种植物的软腐病，导致广泛的组织液化，并分泌多种果胶酶，降解植物细胞壁和中层。通过将克隆的 pehX::TnphoA 片段的标记交换到 E. chrysanthemi CUCPB5010 中，构建了一个在基因 pehX、pelX、pelA、pelB、pelC 和 pelE 中具有定向缺失或插入的 E. chrysanthemi 突变体，这些基因分别编码外切聚-α-D-半乳糖醛酸酶、外聚半乳糖醛酸酶和 4 种果胶裂解酶同工酶。CUCPB5010 是 EC16 的 Delta(pelA pelE) Delta(pelB pelC)::28bp Delta(pelX)Delta4bp 衍生物。这种突变体，E. chrysanthemi CUCPB5012，不再在用于检测细菌果胶裂解活性的标准果胶半固体琼脂培养基中引起凹陷。然而，突变体仍然使菊花（Chrysanthemum morifolium）的叶子液化，尽管毒性降低。在腐烂的菊花组织和最小培养基中，发现突变体产生显著的果胶裂解酶活性，最小培养基中含有菊花提取物或细胞壁作为唯一碳源。活性染色的超薄层等电聚焦凝胶显示，这些制剂中存在几种果胶裂解酶同工酶，pI 范围从极酸到极碱。含有这些同工酶的无菌培养液能够液化菊花叶片组织。与 E. chrysanthemi EC16 中的 pelA、pelB、pelC 和 pelE 基因产物不同，这些植物诱导的果胶裂解酶同工酶在含有果胶的最小培养基中不会产生。结果表明，E. chrysanthemi 产生两组独立调节的果胶裂解酶同工酶，能够液化植物组织。
