Distribution of cell layers in floral organs of chrysanthemum analyzed with periclinal chimeras carrying a transgene...

A fluorescent protein visualized distributions of cell layers in floral organs of chrysanthemum using transgenic periclinal chimeras carrying a gene encoding a fluorescent compound. Plant meristems have three cell layers: the outermost layer (L1), the second layer (L2), and the inner layer (L3). The layers are maintained during development but there is limited knowledge of the details of cell layer patterns within floral organs. In this study, we visualized the distributions of cell layers in floral organs of chrysanthemum using periclinal chimeras carrying a gene encoding a fluorescent compound in the L1 or the L2/L3 layers. The L1 layer contributed most of the epidermal cells of organs including the receptacle, petal, anther, filament, style, stigma, and ovule. The transmitting tissue in the pistil and most of the internal area of the ovule were also derived from the L1. In crossing experiments, no progeny of the L1-chimeric plants showed fluorescence, indicating that the germ cells of chrysanthemum are not derived from the L1 layer. Since anthocyanin pigment is present only in the L1-derived epidermal cells of petals, L1-specific gene integration could be used to alter flower color in commercial cultivars, with a reduced risk of transgene flow from the transgenic chrysanthemums to wild relatives.