Distribution of cell layers in floral organs of chrysanthemum analyzed with periclinal chimeras carrying a transgene encoding fluorescent protein

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.

Metabolite profile comparison of a graft chimera 'Hongrou Huyou' (Citrus changshan-huyou + Citrus unshiu) and its two donor plants

BACKGROUND

Chimeras synthesized artificially by grafting are crucial to the breeding of perennial woody plants. 'Hongrou Huyou' (Citrus changshan-huyou + Citrus unshiu) is a new graft chimera originating from the junction where a Citrus changshan-huyou ("C") scion was top-grafted onto a stock Satsuma mandarin 'Owari' (C. unshiu, "O"). The chimera was named OCC because the cell layer constitutions were O for Layer 1(L1) and C for L2 and L3. In this study, profiles of primary metabolites, volatiles and carotenoids derived from different tissues in OCC and the two donors were investigated, with the aim of determining the relationship between the layer donors and metabolites.

RESULTS

The comparison of the metabolite profiles showed that the amount and composition of metabolites were different between the peels and the juice sacs, as well as between OCC and each of the two donors. The absence or presence of specific metabolites (such as the carotenoids violaxanthin and β-cryptoxanthin, the volatile hydrocarbon germacrene D, and the primary metabolites citric acid and sorbose) in each tissue was identified in the three phenotypes. According to principal component analysis (PCA), overall, the metabolites in the peel of the chimera were derived from donor C, whereas those in the juice sac of the chimera came from donor O.

CONCLUSION

The profiles of primary metabolites, volatiles and carotenoids derived from the peels and juice sacs of OCC and the two donors were systematically compared. The content and composition of metabolites were different between the tissues and between OCC and the each of the two donors. A clear donor dominant pattern of metabolite inheritance was observed in the different tissues of OCC and was basically consistent with the layer origin; the peel of the chimera was derived from C, and the juice sacs of the chimera came from O. These profiles provide potential chemical markers for genotype differentiation, citrus breeding assessment, and donor selection during artificial chimera synthesis.