Assessing the roles of striatin orthologs in fungal morphogenesis, sexual development and pathogenicity

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Assessing the roles of striatin orthologs in fungal morphogenesis, sexual development and pathogenicity


Wang, Chih-Li



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Striatin family proteins contain a caveolin binding domain, a coiled-coil motif, a calmodulin binding domain, and a WD-repeat domain. Homologs of striatin protein have been identified in metazoans and fungi. The mammalian striatin homologs have been proposed to be scaffolding proteins that are involved in multiple signal transduction pathways. However, our knowledge of the function and the molecular mechanism of fungal striatin homologs is limited. Based on the conserved sequences of functional domains, I hypothesized that the fungal striatin orthologs also act as scaffolding proteins that are functionally conserved among fungal species and involved in multiple types of development in the diverse kingdom Mycota.I used reverse genetic strategies to study the function of the Aspergillus nidulans striatin ortholog (strA ) and the Colletotrichum graminicola striatin ortholog ( str1 ). In assays of sexual development, the strA deletion strain (916;strA ) produces fewer ascospores with smaller cleistothecia, while the str1 deletion strain (916;str1 ) is defective in perithecia development. The 916;strA phenotypes indicate that StrA is associated with ascosporogenesis in cleistothecia. Both 916;strA and 916;str1 are reduced in radial growth and in conidia production. The 916;str1 strain is also altered in its spiral growth pattern and morphology of conidia and hyphopodia, but it produces appressoria similar to wild type. The pairing of nitrate non-utilizing mutants demonstrates that Str1 is required for hyphal fusion. In pathogenicity, 916;str1 is less virulent in maize anthracnose leaf blight and stalk rot. The phenotypes of 916;str1 are complemented by the Fusarium verticillioides striatin ortholog (fsr1 ), indicating that Fsr1 and Str1 are functionally conserved. Over-expression of StrA reveals its positive role in conidiation and the sexual production. StrA::eGFP localizes mainly to the endoplasmic reticulum.After comparing the results from these two species and other studied fungal species, I suggest that fungal striatins are involved in five types of development including hyphal growth, hyphal fusion, conidiation, sexual development, and virulence, and propose a model of fungal striatin protein interactions to account for these diverse phenotypes.