Rollins Jeffrey A
Department of Plant Pathology, 1453 Fifield Hall, University of Florida, Gainesville, FL 32611-0680, USA.
Mol Plant Microbe Interact. 2003 Sep;16(9):785-95. doi: 10.1094/MPMI.2003.16.9.785.
The synergistic activities of oxalic acid and endopolygalacturonases are thought to be essential for full virulence of Sclerotinia sclerotiorum and other oxalate-producing plant pathogens. Both oxalic acid production and endopolygalacturonase activity are regulated by ambient pH. Since many gene products with pH-sensitive activities are regulated by the PacC transcription factor in Aspergillus nidulans, we functionally characterized a pacC gene homolog, pac1, from S. sclerotiorum. Mutants with loss-of-function alleles of the pac1 locus were created by targeted gene replacement. In vitro mycelial growth of these pac1 mutants was normal at acidic pH, but growth was inhibited as culture medium pH was increased. Development and maturation of sclerotia in culture was also aberrant in these pac1 replacement mutants. Although oxalic acid production remained alkaline pH-responsive, the kinetics and magnitude of oxalate accumulation were dramatically altered. Additionally, maximal accumulation of endopolygalacturonase gene transcripts (pg1) was shifted to higher ambient pH. Virulence in loss-of-function pac1 mutants was dramatically reduced in infection assays with tomato and Arabidopsis. Based on these results, pac1 appears to be necessary for the appropriate regulation of physiological processes important for pathogenesis and development of S. sclerotiorum.
草酸和内切多聚半乳糖醛酸酶的协同活性被认为对核盘菌和其他产草酸的植物病原体的完全致病性至关重要。草酸的产生和内切多聚半乳糖醛酸酶的活性都受环境pH值的调节。由于在构巢曲霉中许多具有pH敏感活性的基因产物受PacC转录因子调控，我们对来自核盘菌的pacC基因同源物pac1进行了功能鉴定。通过靶向基因替换构建了具有pac1基因座功能缺失等位基因的突变体。这些pac1突变体在酸性pH条件下的体外菌丝生长正常，但随着培养基pH值升高，生长受到抑制。在这些pac1替换突变体中，菌核在培养中的发育和成熟也异常。尽管草酸的产生仍对碱性pH有反应，但草酸盐积累的动力学和量发生了显著变化。此外，内切多聚半乳糖醛酸酶基因转录本（pg1）的最大积累转移到了更高的环境pH值。在对番茄和拟南芥的感染试验中，功能缺失的pac1突变体的毒力显著降低。基于这些结果，pac1似乎对于核盘菌发病机制和发育过程中重要生理过程的适当调节是必需的。
