IBBP, WWU Münster, Münster, Germany.
INRA, BIOGER, Grignon, France.
PLoS Genet. 2014 Jan;10(1):e1004040. doi: 10.1371/journal.pgen.1004040. Epub 2014 Jan 9.
Botrytis cinerea is the causal agent of gray mold diseases in a range of dicotyledonous plant species. The fungus can reproduce asexually by forming macroconidia for dispersal and sclerotia for survival; the latter also participate in sexual reproduction by bearing the apothecia after fertilization by microconidia. Light induces the differentiation of conidia and apothecia, while sclerotia are exclusively formed in the absence of light. The relevance of light for virulence of the fungus is not obvious, but infections are observed under natural illumination as well as in constant darkness. By a random mutagenesis approach, we identified a novel virulence-related gene encoding a GATA transcription factor (BcLTF1 for light-responsive TF1) with characterized homologues in Aspergillus nidulans (NsdD) and Neurospora crassa (SUB-1). By deletion and over-expression of bcltf1, we confirmed the predicted role of the transcription factor in virulence, and discovered furthermore its functions in regulation of light-dependent differentiation, the equilibrium between production and scavenging of reactive oxygen species (ROS), and secondary metabolism. Microarray analyses revealed 293 light-responsive genes, and that the expression levels of the majority of these genes (66%) are modulated by BcLTF1. In addition, the deletion of bcltf1 affects the expression of 1,539 genes irrespective of the light conditions, including the overexpression of known and so far uncharacterized secondary metabolism-related genes. Increased expression of genes encoding alternative respiration enzymes, such as the alternative oxidase (AOX), suggest a mitochondrial dysfunction in the absence of bcltf1. The hypersensitivity of Δbctlf1 mutants to exogenously applied oxidative stress--even in the absence of light--and the restoration of virulence and growth rates in continuous light by antioxidants, indicate that BcLTF1 is required to cope with oxidative stress that is caused either by exposure to light or arising during host infection.
灰葡萄孢（Botrytis cinerea）是一系列双子叶植物病原菌，可引起灰霉病。该真菌可通过形成用于传播的大型分生孢子和用于生存的菌核进行无性繁殖；后者也可通过微孢子受精后产生子囊壳参与有性繁殖。光照可诱导分生孢子和子囊壳的分化，而菌核则仅在光照缺失时形成。光照对真菌毒力的相关性尚不清楚，但在自然光照射和持续黑暗下都观察到了感染。通过随机诱变方法，我们鉴定了一个新的与毒力相关的基因，该基因编码一个 GATA 转录因子（光响应 TF1 的 BcLTF1），在构巢曲霉（NsdD）和粗糙脉孢菌（SUB-1）中有特征性同源物。通过 bcltf1 的缺失和过表达，我们证实了该转录因子在毒力中的预测作用，并发现其在光照依赖性分化、活性氧（ROS）产生和清除之间的平衡以及次生代谢的调节中的功能。微阵列分析显示了 293 个光响应基因，其中这些基因的大多数（66%）的表达水平受到 BcLTF1 的调节。此外，bcltf1 的缺失影响了 1539 个基因的表达，无论光照条件如何，包括已知和迄今为止未表征的次生代谢相关基因的过表达。替代呼吸酶（如替代氧化酶（AOX））基因的表达增加表明，在缺乏 bcltf1 的情况下，线粒体功能受损。Δbctlf1 突变体对外源氧化应激的敏感性增加——即使在没有光照的情况下——以及抗氧化剂在持续光照下恢复毒力和生长速率，表明 BcLTF1 是应对由暴露于光或在宿主感染期间产生的氧化应激所必需的。
