BioProject

Somatic embryogenesis in nucellar tissues is widely recognized to induce polyembryony in major citrus varieties such as sweet oranges, satsuma mandarins and lemons. More...

Somatic embryogenesis in nucellar tissues is widely recognized to induce polyembryony in major citrus varieties such as sweet oranges, satsuma mandarins and lemons. This capability for apomixis is attractive in agricultural production systems using hybrid seeds, and many studies have been performed to elucidate the molecular mechanisms of various types of apomixis. To identify the gene responsible for somatic embryogenesis in citrus, a custom oligo-DNA microarray including predicted genes in the citrus polyembryonic locus was used to compare the expression profiles in reproductive tissues between monoembryonic and polyembryonic varieties. The full length of CitRKD1, which was identified as a candidate gene responsible for citrus somatic embryogenesis, was isolated from satsuma mandarin and its molecular function was investigated using transgenic ‘Hamlin’ sweet orange by antisense-overexpression. The candidate gene CitRKD1, predominantly transcribed in reproductive tissues of polyembryonic varieties, is a member of the plant RWP-RK domain proteins. CitRKD1 of satsuma mandarin comprised two alleles (CitRKD1-mg1 and CitRKD1-mg2) at the polyembryonic locus controlling embryony type (mono/polyembryony) that were structurally divided into two types with or without a miniature inverted-repeat transposable element (MITE)-like insertion in the upstream region. CitRKD1-mg2 with the MITE insertion was the predominant transcript in flowers and young fruits where somatic embryogenesis of nucellar cells occurred. Loss of CitRKD1 function by antisense-overexpression abolished somatic embryogenesis in transgenic sweet orange and the transgenic T1 plants were confirmed to derive from zygotic embryos produced by self-pollination by DNA diagnosis. Genotyping PCR analysis of 95 citrus traditional and breeding varieties revealed that the CitRKD1 allele with the MITE insertion (polyembryonic allele) was dominant and major citrus varieties with the polyembryonic allele produced polyembryonic seeds. Overall design: To identify the gene responsible for somatic embryogenesis in citrus, a custom oligo-DNA microarray including predicted genes in the citrus polyembryonic locus was used to compare the expression profiles in reproductive tissues between ‘Kiyomi’ and ‘Harumi’ as materials for monoembryonic and polyembryonic varieties, respectively. Eight independent experiment performed at 15, 30, 45 and 60 DAF (Day After Flowering) using whole young fruits in each variety. Less...