Institute of Biotechnology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, China.
Appl Microbiol Biotechnol. 2013 Oct;97(20):9087-98. doi: 10.1007/s00253-013-5129-x. Epub 2013 Aug 6.
Penicillium digitatum is the most important postharvest pathogen of citrus fruits. Along disease progression, the infected citrus peel tissue is acidified due to the accumulation of organic acids. So far, relatively little is known about the environmental factors that regulate pathogenicity in this fungus. In this study, the role of the pH signaling transcription factor PacC in the pathogenesis of P. digitatum was investigated. We identified the pacC ortholog (PdpacC) in P. digitatum and found that its transcript levels were elevated under alkaline conditions (pH ≥ 7) in vitro, as well as during the infection of citrus fruits in spite of the low pH (about 3.0 to 3.5) of the macerated tissue. Na(+) and pectin also induced the expression of PdpacC. Disruption of PdpacC resulted in impaired mycelial growth under neutral or alkaline pH conditions and on synthetic medium supplemented with pectin as the sole carbon source, and attenuated virulence towards citrus fruits. Introducing the full length of PdpacC into the ΔPdpacC mutant restored all these phenotypes. The expression of the polygalacturonase gene Pdpg2 and pectin lyase gene Pdpnl1 in P. digitatum was upregulated in the wild type strain but not or weakly upregulated in the ΔPdpacC mutant during infection. Disruption of Pdpg2 also resulted in attenuated virulence of P. digitatum towards citrus fruits. Collectively, we conclude that PdPacC plays an important role in pathogenesis of P. digitatum via regulation of the expression of cell wall degradation enzyme genes, such as Pdpg2 and Pdpnl1.
青霉属是柑橘类水果最重要的采后病原体。随着疾病的发展，受感染的柑橘果皮组织由于有机酸的积累而酸化。到目前为止，关于调节这种真菌致病性的环境因素，人们知之甚少。在这项研究中，研究了 pH 信号转录因子 PacC 在青霉属中的致病性作用。我们在青霉属中鉴定了 pacC 直系同源物（PdpacC），并发现其转录水平在体外碱性条件（pH≥7）下以及柑橘果实感染过程中升高，尽管组织的 pH 值较低（约 3.0 至 3.5）。Na+和果胶也诱导 PdpacC 的表达。PdpacC 的破坏导致中性或碱性 pH 条件下和在补充果胶作为唯一碳源的合成培养基中菌丝生长受损，并且对柑橘果实的毒力减弱。将 PdpacC 的全长引入ΔPdpacC 突变体中恢复了所有这些表型。在野生型菌株中，多聚半乳糖醛酸酶基因 Pdpg2 和果胶裂解酶基因 Pdpnl1 的表达在感染过程中上调，但在ΔPdpacC 突变体中上调不明显或较弱。Pdpg2 的破坏也导致青霉属对柑橘果实毒力减弱。总之，我们得出结论，PdPacC 通过调节细胞壁降解酶基因（如 Pdpg2 和 Pdpnl1）的表达，在青霉属的发病机制中发挥重要作用。
