Matthysse A G, McMahan S
Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.
Appl Environ Microbiol. 2001 Mar;67(3):1070-5. doi: 10.1128/AEM.67.3.1070-1075.2001.
Infections of wound sites on dicot plants by Agrobacterium tumefaciens result in the formation of crown gall tumors. An early step in tumor formation is bacterial attachment to the plant cells. AttR mutants failed to attach to wound sites of both legumes and nonlegumes and were avirulent on both groups of plants. AttR mutants also failed to attach to the root epidermis and root hairs of nonlegumes and had a markedly reduced ability to colonize the roots of these plants. However, AttR mutants were able to attach to the root epidermis and root hairs of alfalfa, garden bean, and pea. The mutant showed little reduction in its ability to colonize these roots. Thus, A. tumefaciens appears to possess two systems for binding to plant cells. One system is AttR dependent and is required for virulence on all of the plants tested and for colonization of the roots of all of the plants tested except legumes. Attachment to root hairs through this system can be blocked by the acetylated capsular polysaccharide. The second system is AttR independent, is not inhibited by the acetylated capsular polysaccharide, and allows the bacteria to bind to the roots of legumes.
根癌土壤杆菌感染双子叶植物的伤口部位会导致冠瘿瘤的形成。肿瘤形成的早期步骤是细菌附着于植物细胞。AttR突变体无法附着于豆类和非豆类植物的伤口部位，并且对这两类植物均无致病性。AttR突变体也无法附着于非豆类植物的根表皮和根毛，并且在这些植物根部定殖的能力显著降低。然而，AttR突变体能够附着于苜蓿、菜豆和豌豆的根表皮和根毛。该突变体在这些根部定殖的能力几乎没有降低。因此，根癌土壤杆菌似乎拥有两种与植物细胞结合的系统。一种系统依赖AttR，对于所有测试植物的致病性以及除豆类植物外所有测试植物根部的定殖都是必需的。通过该系统与根毛的附着可被乙酰化荚膜多糖阻断。第二种系统不依赖AttR，不受乙酰化荚膜多糖的抑制，并使细菌能够与豆类植物的根部结合。
