Hauck Paula, Thilmony Roger, He Sheng Yang
Department of Energy Plant Research Laboratory and Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA.
Proc Natl Acad Sci U S A. 2003 Jul 8;100(14):8577-82. doi: 10.1073/pnas.1431173100. Epub 2003 Jun 19.
Bacterial effector proteins secreted through the type III secretion system (TTSS) play a crucial role in causing plant and human diseases. Although the ability of type III effectors to trigger defense responses in resistant plants is well understood, the disease-promoting functions of type III effectors in susceptible plants are largely enigmatic. Previous microscopic studies suggest that in susceptible plants the TTSS of plant-pathogenic bacteria transports suppressors of a cell wall-based plant defense activated by the TTSS-defective hrp mutant bacteria. However, the identity of such suppressors has remained elusive. We discovered that the Pseudomonas syringae TTSS down-regulated the expression of a set of Arabidopsis genes encoding putatively secreted cell wall and defense proteins in a salicylic acid-independent manner. Transgenic expression of AvrPto repressed a similar set of host genes, compromised defense-related callose deposition in the host cell wall, and permitted substantial multiplication of an hrp mutant. AvrPto is therefore one of the long postulated suppressors of an salicylic acid-independent, cell wall-based defense that is aimed at hrp mutant bacteria.
通过III型分泌系统（TTSS）分泌的细菌效应蛋白在引发植物和人类疾病中起着关键作用。尽管III型效应子在抗性植物中触发防御反应的能力已得到充分了解，但III型效应子在感病植物中的致病促进功能在很大程度上仍不明确。先前的显微镜研究表明，在感病植物中，植物病原菌的TTSS转运由TTSS缺陷型hrp突变细菌激活的基于细胞壁的植物防御的抑制因子。然而，此类抑制因子的身份仍然难以捉摸。我们发现丁香假单胞菌TTSS以水杨酸非依赖的方式下调了一组拟南芥基因的表达，这些基因编码推定的分泌型细胞壁和防御蛋白。AvrPto的转基因表达抑制了一组类似的宿主基因，损害了宿主细胞壁中与防御相关的胼胝质沉积，并允许hrp突变体大量繁殖。因此，AvrPto是长期以来推测的针对hrp突变细菌的水杨酸非依赖型、基于细胞壁的防御的抑制因子之一。
