Journal of Bioenergetics and Biomembranes

, Volume 27, Issue 4, pp 437-445

First online:

URF13, a ligand-gated, pore-forming receptor for T-toxin in the inner membrane ofcms-T mitochondria

  • David M. RhoadsAffiliated withDepartment of Botany/Developmental, Cell, and Molecular Biology Group, Duke UniversityDepartment of Genetics, North Carolina State University
  • , Charles S. LevingsIIIAffiliated withDepartment of Genetics, North Carolina State University
  • , James N. SiedowAffiliated withDepartment of Botany/Developmental, Cell, and Molecular Biology Group, Duke University

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URF13 is the product of a mitochondrial-encoded gene (T-urfl3) found only in maize plants containing the Texas male-sterile cytoplasm (cms-T), and it is thought to be responsible for both cytoplasmic male sterility and the susceptibility ofcms-T maize to the fungal pathogensBipolaris maydis race T andPhyllosticta maydis. Mitochondria isolated fromcms-T maize are uniquely sensitive to pathotoxins (T-toxin) produced by these fungi and to methomyl (a commercial insecticide). URF13 acts as a receptor that specifically binds T-toxin to produce hydrophilic pores in the inner mitochondrial membrane. When expressed inEscherichia coli cells, URF13 also forms hydrophilic pores in the plasma membrane if exposed to T-toxin or methomyl. Topological studies established that URF13 contains three membrane-spanning α-helices, two of which are amphipathic and can contribute to pore formation. Chemical crosslinking of URF13 was used to demonstrate the existence of URF13 oligomers incms-T mitochondria andE. coli cells. The ability of the carboxylate-specific reagent,N,N∼-dicyclohexycarbodiimide, to cross-link URF13 was used in conjunction with site-directed mutagenesis to establish that the URF13 tetramer has a central core consisting of a four-α-helical bundle which undergoes a conformational change after interaction with T-toxin or methomyl. Overall, the experimental evidence indicates that URF13 functions as a ligand-gated, pore-forming T-toxin receptor incms-T mitochondria.

Key words

Maize mitochondria cytoplasmic male sterility URF13 T-urf13 T-toxin pathogenesis pore-forming receptor