Unusual and Typical Features of a Novel Restorer-Of-Fertility Gene of Sugar Beet (Beta Vulgaris L.)
INVESTIGATION Unusual and Typical Features of a Novel Restorer-of-Fertility Gene of Sugar Beet (Beta vulgaris L.) Hiroaki Matsuhira,*,1 Hiroyo Kagami,* Masayuki Kurata,* Kazuyoshi Kitazaki,*,2 Muneyuki Matsunaga,* Yuko Hamaguchi,* Eiki Hagihara,* Minoru Ueda,* Michiyo Harada,* Aki Muramatsu,* Rika Yui-Kurino,* Kazunori Taguchi,† Hideto Tamagake,‡ Tetsuo Mikami,* and Tomohiko Kubo*,3 *Laboratory of Genetic Engineering, Research Faculty of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan, †Memuro Upland Farming Research Station, Hokkaido Agricultural Research Center, National Agriculture and Food Research Organization, Memuro, Hokkaido 082-0081, Japan, and ‡Central Agricultural Experiment Station, Agriculture Research Department, Hokkaido Research Organization, Takikawa 073-0013, Japan ABSTRACT Male gametogenesis in plants can be impaired by an incompatibility between nuclear and mitochondrial genomes, termed cytoplasmic male sterility (CMS). A sterilizing factor resides in mitochondria, whereas a nuclear factor, Restorer-of-fertility (Rf), restores male fertility. Although a majority of plant Rf genes are thought to encode a family of RNA-binding proteins called pentatrico-peptide repeat (PPR) proteins, we isolated a novel type of Rf from sugar beet. Two BACs and one cosmid clone that constituted a 383-kbp contig covering the sugar beet Rf1 locus were sequenced. Of 41 genes borne by the contig, quadruplicated genes were found to be associated with specific transcripts in Rf1 flower buds. The quadruplicated genes encoded a protein resembling OMA1, a protein known from yeast and mammals to be involved in mitochondrial protein quality control. Construction of transgenic plants revealed that one of the four genes (bvORF20) was capable of restoring partial pollen fertility to CMS sugar beet; the level of restoration was comparable to that evaluated by a crossing experiment.
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