Zhou N, Tootle T L, Glazebrook J
Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA.
Plant Cell. 1999 Dec;11(12):2419-28. doi: 10.1105/tpc.11.12.2419.
Phytoalexins are low molecular weight antimicrobial compounds that are synthesized in response to pathogen attack. The phytoalexin camalexin, an indole derivative, is produced by Arabidopsis in response to infection with the bacterial pathogen Pseudomonas syringae. The phytoalexin deficient 3 (pad3) mutation, which causes a defect in camalexin production, has no effect on resistance to P. syringae but compromises resistance to the fungal pathogen Alternaria brassicicola. We have now isolated PAD3 by map-based cloning. The predicted PAD3 protein appears to be a cytochrome P450 monooxygenase, similar to those from maize that catalyze synthesis of the indole-derived secondary metabolite 2,4-dihydroxy-1, 4-benzoxazin-3-one. The expression of PAD3 is tightly correlated with camalexin synthesis and is regulated by PAD4 and PAD1. On the basis of these findings, we conclude that PAD3 almost certainly encodes an enzyme required for camalexin biosynthesis. Moreover, these results strongly support the idea that camalexin does not play a major role in plant resistance to P. syringae infection, although it is involved in resistance to a fungal pathogen.
植保素是一类低分子量的抗菌化合物，在植物受到病原体攻击时合成。植保素camalexin是一种吲哚衍生物，由拟南芥在受到细菌病原体丁香假单胞菌感染时产生。植保素缺陷3（pad3）突变导致camalexin产生缺陷，对丁香假单胞菌的抗性没有影响，但会损害对真菌病原体芸苔链格孢的抗性。我们现在通过图位克隆分离出了PAD3。预测的PAD3蛋白似乎是一种细胞色素P450单加氧酶，与玉米中催化吲哚衍生的次生代谢物2,4-二羟基-1,4-苯并恶嗪-3-酮合成的酶相似。PAD3的表达与camalexin的合成紧密相关，并受PAD4和PAD1调控。基于这些发现，我们得出结论，PAD3几乎肯定编码camalexin生物合成所需的一种酶。此外，如果这些结果有力地支持了这样一种观点，即camalexin在植物对丁香假单胞菌感染的抗性中不发挥主要作用，尽管它参与了对真菌病原体的抗性。
