Glazebrook J, Ausubel F M
Department of Genetics, Harvard Medical School, Boston, MA 02114.
Proc Natl Acad Sci U S A. 1994 Sep 13;91(19):8955-9. doi: 10.1073/pnas.91.19.8955.
A genetic approach was used to assess the extent to which a particular plant defense response, phytoalexin biosynthesis, contributes to Arabidopsis thaliana resistance to Pseudomonas syringae pathogens. The A. thaliana phytoalexin, camalexin, accumulated in response to infection by various P. syringae strains. No correlation between pathogen avirulence and camalexin accumulation was observed. A biochemical screen was used to isolate three mutants of A. thaliana ecotype Columbia that were phytoalexin deficient (pad mutants). The mutations pad1, pad2, and pad3 were found to be recessive alleles of three different genes. pad1 and pad2 were mapped to chromosome IV and pad3 was mapped to chromosome III. Infection of pad mutant plants with strains carrying cloned avirulence genes revealed that the pad mutations did not affect the plants' ability to restrict the growth of these strains. This result strongly suggests that in A. thaliana, phytoalexin biosynthesis is not required for resistance to avirulent P. syringae pathogens. Two of the pad mutants displayed enhanced sensitivity to isogenic virulent P. syringae pathogens, suggesting that camalexin may serve to limit the growth of virulent bacteria.
采用遗传学方法来评估一种特定的植物防御反应——植保素生物合成，在多大程度上有助于拟南芥对丁香假单胞菌病原体产生抗性。拟南芥植保素——camalexin，会在受到各种丁香假单胞菌菌株感染时积累。未观察到病原体无毒力与camalexin积累之间存在相关性。利用生化筛选方法分离出了拟南芥生态型哥伦比亚的三个植保素缺陷型突变体（pad突变体）。发现pad1、pad2和pad3突变是三个不同基因的隐性等位基因。pad1和pad2被定位到第四条染色体上，pad3被定位到第三条染色体上。用携带克隆无毒力基因的菌株感染pad突变体植物，结果表明pad突变并不影响植物限制这些菌株生长的能力。这一结果有力地表明，在拟南芥中，对无毒丁香假单胞菌病原体产生抗性并不需要植保素生物合成。其中两个pad突变体对同基因的毒性丁香假单胞菌病原体表现出增强的敏感性，这表明camalexin可能有助于限制毒性细菌的生长。
