**4.** *Ustilago maydis*

*U. maydis* is a fungus in the Division *Basidiomycota*. It is a plant pathogen that causes corn smut. *U. maydis* teliospores are thick-walled rounded melanized cells with diploid nuclei that are capable of tolerating extreme temperatures and desiccation. Before teliospores mature in the infected corn plant, meiosis is initiated [29]. As teliospores germinate they complete meiosis to produce four haploid basidiospores [29].

Plants often defend themselves from pathogenic microbial invasion by releasing an oxidative burst that includes the production of reactive oxygen species [30]. *U. maydis* can protect against the host oxidative attack by an oxidative stress response [30]. In protecting against oxidative DNA damage, *U. maydis* employs a recombinational DNA repair system that includes the Rad51 protein (related to mammalian

Rad51), a Rec2 protein (more distantly related to mammalian Rad51), and the Brh2 protein [that is related to the mammalian Breast Cancer 2 (Brca2) protein)] [31]. When any of these proteins is inactive, *U. maydis* becomes more sensitive to DNA damaging agents, mitotic recombination is reduced, and there is failure to complete meiosis [31]. Recombinational repair occurring during meiosis as teliospores are formed by the pathogen likely contributes to the maintenance of its genome integrity by removing DNA damages incurred during infection.
