Threonine synthase CoTHR4 is involved in infection-related morphogenesis during the pre-penetration stage in Colletotrichum orbiculare

• Published in: Microbial pathogenesis Vol. 137; p. 103746
• Main Authors: Harata, Ken, Okuno, Tetsuro
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-12-2019
• Subjects: Agrobacterium tumefaciens - genetics; Amino Acid Sequence; Appressorium; Carbon-Oxygen Lyases - genetics; Carbon-Oxygen Lyases - metabolism; Colletotrichum - enzymology; Colletotrichum - genetics; Colletotrichum - pathogenicity; Colletotrichum orbiculare; Conidiation; Cucumis sativus; Gene Expression Regulation, Fungal; Germination; Hyphae - growth & development; Infections; Morphogenesis; Mutation; Pathogenicity; Phenotype; Plant Diseases - microbiology; Saccharomyces cerevisiae - genetics; Sequence Alignment; Sequence Homology, Amino Acid; Spores, Fungal - metabolism; Threonine; Threonine - metabolism; Threonine synthase; Virulence; Pathogenicity; Threonine; Threonine synthase; Conidiation; Germination; Appressorium; Colletotrichum orbiculare
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/j.micpath.2019.103746

Upon recognition of host plants, Colletotrichum orbiculare, an anthracnose disease fungus of cucurbitaceous plants, initiates morphological differentiation, including conidial germination and appressorium formation on the cuticle layer. The series of infection processes of C. orbiculare requires enormous nutrient and energy, but the surface of the cucurbitaceous hosts is hardly nutrient-rich. Hence, C. orbiculare must exert tight management of its intracellular nutrients in order to properly induce infection-related morphogenesis. Here, we carried out a large-scale insertional mutagenesis screen using Agrobacterium tumefaciens-mediated transformation to identify novel genes involved in the pathogenicity of C. orbiculare and found that CoTHR4-encoded threonine synthase, a homolog of Saccharomyces cerevisiae THR4, is required for pathogenicity and conidiation in C. orbiculare. Threonine supplementation allowed the cothr4 mutant to produce conidia to a level equivalent to that of the wild-type. The conidia produced from the threonine-treated cothr4 mutant failed to germinate in the absence of threonine, but retained the ability to germinate and to form appressoria in the presence of threonine. However, the conidia produced from the threonine-treated cothr4 mutant remained attenuated in pathogenicity on cucumber cotyledons even in the presence of threonine. Cytorrhysis assays revealed that appressoria of the cothr4 mutant induced by exogenous threonine treatment showed low turgor generation. Taken together, these results showed that threonine synthase CoThr4 plays a pivotal role in infection-related morphogenesis during the pre-penetration stage of C. orbiculare.
•Threonine synthase CoTHR4 was identified by a large-scale forward genetic screening.•CoTHR4 is involved in hyphal growth, conidiation and pathogenicity.•Threonine was synthesized and accumulated in ungerminated conidia.•The cothr4 mutant formed non-functional appressoria in the presence of threonine.