Maize gene expression during infection with Colletotrichum graminicola

The hemibiotrophic fungal pathogen Colletotrichum graminicola is the causal agent of anthracnose disease on maize stalks and leaves. After the formation of appressoria the host cell wall is penetrated by the conversion of appressorial turgor pressure into forceful ejection of a penetration peg. Subsequently, C. graminicola establishes biotrophic hyphae in the penetrated epidermis cell at around 36 hours post inoculation (hpi) until a switch of hyphal morphology and lifestyle takes place during the colonization of neighboring host cells at around 72 hpi. During the ensuing necrotrophic growth, dark necrotic lesions are formed that are visible as anthracnose symptoms. We used microarrays to detail the global programme of gene expression during the infection process of Colletotrichum graminicola in its host plant to get insight into the defense response of this compatible interaction and into the metabolic reprogramming needed to supply the fungus with nutrients. In three independent experiments, maize plants were infected with conidia of the Colletotrichum graminicola strain CgM2 by spray inoculation of leaves. Samples from infected leaves were taken at 36 and 96 hours post infection, corresponding to initial biotrophic and necrotrophic phase, respectively. Samples from uninfected control plants were taken at the same time points.

半活体营养型真菌病原菌禾谷炭疽菌（Colletotrichum graminicola）是引发玉米茎秆与叶片炭疽病的致病菌。当附着胞（appressorium）形成后，病原菌通过将附着胞膨压转化为侵入钉的强力弹射，穿透宿主细胞壁。随后，禾谷炭疽菌会在接种后约36小时（hours post inoculation，简称hpi）于被穿透的表皮细胞中形成活体营养菌丝，直至接种后约72小时，在侵染邻近宿主细胞的过程中发生菌丝形态与生活方式的转换。在随后的死体营养生长阶段，会形成黑色坏死病斑，此即为炭疽病的可见症状。本研究通过基因芯片（microarray）详细解析了禾谷炭疽菌侵染宿主植物过程中的全局基因表达谱，以期深入探究该亲和互作中的宿主防御反应，以及为真菌获取营养所需的代谢重编程机制。在三次独立实验中，研究团队采用喷雾接种（spray inoculation）叶片的方式，用禾谷炭疽菌CgM2菌株的分生孢子（conidia）侵染玉米植株。分别于接种后36小时（对应初始活体营养阶段）和96小时（对应死体营养阶段）采集侵染叶片样本；同时在相同时间点采集未接种的对照植株样本。