Pro-domain processing of fungal effector proteins from plant pathogens

Abstract

Fungal effector proteins that are processed by proteases can be broadly separated into 2 classes (Fig 1A). The first class are effectors that function as bioactive peptides. Repeat-containing effectors have been identified in several fungal plant pathogens, the most well characterised are those originating from the maize pathogenic fungus Ustilago maydis. In U. maydis, 15 repeatcontaining proteins have been identified. Of these, 8 appear to be processed into multiple short peptides by the calcium-dependent subtilisin-like serine protease Kex2 (kexin; E. C.3.4.21.61) [1]. One example, Rep1, is processed into multiple short peptides by Kex2 during secretion from the fungus. The generated peptides are biologically active and form tightly bound amyloid-like fibrils on the hyphal surface that repel water and facilitate the proper formation of aerial hyphae and hyphal attachment [2,3]. Additionally, some classes of ribosomally synthesised and post-translationally modified peptides (RiPPs) are known to be processed by a Kex2-like protease (recently reviewed by [4]). Examples include Victorin, a host-selective toxin produced by the oat pathogen Cochliobolus victoriae [5], and epichloe cyclins from Epichlo festucae, though their biological function remains unknown [6].

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