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Role of the 4-Phosphopantetheinyl Transferase of Trichoderma virens in Secondary Metabolism and Induction of Plant Defense Responses

¹Laboratorio Nacional de Genómica para la Biodiversidad and Departamento de Ingeniería Genética de Plantas, CINVESTAV Irapuato, CP 36821, Irapuato, Gto., México; ²Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigaciones Químico-Biológicas, Ciudad Universitaria, CP 58036 Morelia; Michoacán, México; ³Universidad Nacional Autónoma de México, Instituto de Fisiología Celular, Departamento de Biología Celular y Desarrollo, Circuito Exterior S/N Ciudad Universitaria, Coyoacán, 04510, México, D.F.; ⁴División de Biología Molecular, Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San José 2055, Col. Lomas 4 sección CP 78216, San Luis Potosí S.L.P., México

Trichoderma virens is a ubiquitous soil fungus successfully used in biological control due to its efficient colonization of plant roots. In fungi, 4-phosphopantetheinyl transferases (PPTases) activate enzymes involved in primary and secondary metabolism. Therefore, we cloned the PPTase gene ppt1 from T. virens and generated PPTase-deficient (Δppt1) and overexpressing strains to investigate the role of this enzyme in biocontrol and induction of plant defense responses. The Δppt1 mutants were auxotrophic for lysine, produced nonpigmented conidia, and were unable to synthesize nonribosomal peptides. Although spore germination was severely compromised under both low and high iron availability, mycelial growth occurred faster than the wild type, and the mutants were able to efficiently colonize plant roots. The Δppt1 mutants were unable of inhibiting growth of phytopathogenic fungi in vitro. Arabidopsis thaliana seedlings co-cultivated with wild-type T. virens showed increased expression of pPr1a:uidA and pLox2:uidA markers, which correlated with enhanced accumulation of salicylic acid (SA), jasmonic acid, camalexin, and resistance to Botrytis cinerea. Co-cultivation of A. thaliana seedlings with Δppt1 mutants compromised the SA and camalexin responses, resulting in decreased protection against the pathogen. Our data reveal an important role of T. virens PPT1 in antibiosis and induction of SA and camalexin-dependent plant defense responses.