Liu Xiaoguang, Inlow Mark, VanEtten Hans D
Department of Plant Pathology, University of Arizona, Tucson, AZ 85721, USA.
Curr Genet. 2003 Nov;44(2):95-103. doi: 10.1007/s00294-003-0428-x. Epub 2003 Aug 19.
A cluster of pathogenicity genes ( PEP1, PEP2, PDA1, PEP5), termed the pea pathogenicity ( PEP) cluster and located on a 1.6-Mb conditionally dispensable (CD) chromosome, was identified in the fungal pathogen Nectria haematococca. Studies determined that the expression of PDA1 is induced in both infected pea tissues and in vitro by the phytoalexin pisatin. The present study reports the use of real-time quantitative RT-PCR to monitor the expression of each PEP gene and PDA1. In mycelia actively growing in culture, the mRNA levels of PEP1, PEP5 and PDA1 were very low and the PEP2 transcript was undetectable. In planta, PDA1 and PEP2 were strongly induced, while PEP1 and PEP5 were moderately induced. Starvation slightly enhanced the expression of PEP1, PDA1 and PEP5, while the expression of PEP2 remained undetectable. Exposure to pisatin in culture stimulated the expression of PDA1 and each PEP gene to a similar level as occurred in planta. In addition, all four pathogenicity genes displayed similar temporal patterns of expression in planta and in vitro, consistent with a coordinated regulation of these genes by pisatin during pea pathogenesis. In the flanking regions of the PEP cluster, six open reading frames (ORFs) were identified and all were expressed during infection of pea. Comparison of the codon preferences of these ORFs and seven additional genes from CD chromosomes with the codon preferences of 21 genes from other chromosomes revealed there is a codon bias that correlates with the source of the genes. This difference in codon bias is consistent with the hypothesis that genes on the CD chromosome have a different origin from genes of normal chromosomes, suggesting that horizontal gene transfer may have played a role in the evolution of pathogenesis in N. haematococca.
在真菌病原体血座壳菌中鉴定出了一组致病基因（PEP1、PEP2、PDA1、PEP5），称为豌豆致病（PEP）簇，位于一条1.6兆碱基的条件性可缺失（CD）染色体上。研究确定，PDA1的表达在受感染的豌豆组织中和体外均受到植物抗毒素豌豆素的诱导。本研究报告了使用实时定量RT-PCR来监测每个PEP基因和PDA1的表达。在培养中活跃生长的菌丝体中，PEP1、PEP5和PDA1的mRNA水平非常低，且未检测到PEP2转录本。在植物体内，PDA1和PEP2被强烈诱导，而PEP1和PEP5被中度诱导。饥饿略微增强了PEP1、PDA1和PEP5的表达，而PEP2的表达仍未检测到。在培养中暴露于豌豆素会刺激PDA1和每个PEP基因的表达，使其达到与植物体内相似的水平。此外，所有四个致病基因在植物体内和体外均表现出相似的表达时间模式，这与豌豆发病过程中这些基因受豌豆素的协同调控一致。在PEP簇的侧翼区域，鉴定出了六个开放阅读框（ORF），并且在豌豆感染期间均有表达。将这些ORF以及来自CD染色体的另外七个基因的密码子偏好与来自其他染色体的21个基因的密码子偏好进行比较，发现存在与基因来源相关的密码子偏好。密码子偏好的这种差异与CD染色体上的基因与正常染色体上的基因起源不同的假设一致，这表明水平基因转移可能在血座壳菌致病机制的进化中发挥了作用。
