Figure 1.

Infection structure development and effector localization in Colletotrichum higginsianum. (A) Appressorial formation on the leaf surface at 24 hpi. Spores (S) adhere to the host cuticle and produce a germ tube (GT), and an appressorium (A) is formed to penetrate plant epidermal cells directly. Effectors, marked with yellow dots, accumulate at the appressorial pore (AP) and then are secreted from the pore; (B) the biotrophic infection phase at 40 hpi. A penetration peg (PP) develops from the base of the appressorium and penetrates the host cuticle and cell wall. Primary biotrophic hyphae (BH) develop inside the epidermal cell and invaginate the plant plasma membrane. The host protoplast remains alive during this biotrophic stage of the interaction. Effectors accumulate at the biotrophic interfacial bodies, the yellow layer outside the primary hyphae, and then are secreted to the host cell from the biotrophic interfacial bodies; (C) the necrotrophic infection phase at 55 hpi. Secondary necrotrophic hyphae (NH) later develop from the BH and spread into the surrounding cells without biotrophic interfacial bodies and directly penetrate host cytoplasm. The host epidermal cell shaded in dark gray then dies after NH production. All graphics were derived from original micrographs for easier visualization.