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G3 (Bethesda). 2018 Jan 4;8(1):291-302. doi: 10.1534/g3.117.300304.

Restorer-of-Fertility Mutations Recovered in Transposon-Active Lines of S Male-Sterile Maize.

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Department of Plant Biology, University of Illinois, Urbana, Illinois 61801.
Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611.
Tropical Agriculture Research Station, The United States Department of Agriculture, Agriculture Research Service, Mayaguez, Puerto Rico 00680-5470.
Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, Iowa 50011.
Department of Agronomy, Iowa State University, Ames, Iowa 50011.
Florida Medical Entomology Laboratory, Vero Beach, Florida 32962.
Biology Department, New Jersey City University, Jersey City, NJ 07305.
Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611


Mitochondria execute key pathways of central metabolism and serve as cellular sensing and signaling entities, functions that depend upon interactions between mitochondrial and nuclear genetic systems. This is exemplified in cytoplasmic male sterility type S (CMS-S) of Zea mays, where novel mitochondrial open reading frames are associated with a pollen collapse phenotype, but nuclear restorer-of-fertility (restorer) mutations rescue pollen function. To better understand these genetic interactions, we screened Activator-Dissociation (Ac-Ds), Enhancer/Suppressor-mutator (En/Spm), and Mutator (Mu) transposon-active CMS-S stocks to recover new restorer mutants. The frequency of restorer mutations increased in transposon-active stocks compared to transposon-inactive stocks, but most mutants recovered from Ac-Ds and En/Spm stocks were unstable, reverting upon backcrossing to CMS-S inbred lines. However, 10 independent restorer mutations recovered from CMS-S Mu transposon stocks were stable upon backcrossing. Many restorer mutations condition seed-lethal phenotypes that provide a convenient test for allelism. Eight such mutants recovered in this study included one pair of allelic mutations that were also allelic to the previously described rfl2-1 mutant. Targeted analysis of mitochondrial proteins by immunoblot identified two features that consistently distinguished restored CMS-S pollen from comparably staged, normal-cytoplasm, nonmutant pollen: increased abundance of nuclear-encoded alternative oxidase relative to mitochondria-encoded cytochrome oxidase and decreased abundance of mitochondria-encoded ATP synthase subunit 1 compared to nuclear-encoded ATP synthase subunit 2. CMS-S restorer mutants thus revealed a metabolic plasticity in maize pollen, and further study of these mutants will provide new insights into mitochondrial functions that are critical to pollen and seed development.


cytoplasmic male sterility; gametophyte; mitochondria; pollen; seed

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