Retrotransposons control fruit-specific, cold-dependent accumulation of anthocyanins in blood oranges.

Traditionally, Sicilian blood oranges (Citrus sinensis) have been associated with cardiovascular health, and consumption has been shown to prevent obesity in mice fed a high-fat diet. Despite increasing consumer interest in these health-promoting attributes, production of blood oranges remains unreliable due largely to a dependency on cold for full color formation. We show that Sicilian blood orange arose by insertion of a Copia-like retrotransposon adjacent to a gene encoding Ruby, a MYB transcriptional activator of anthocyanin production. The retrotransposon controls Ruby expression, and cold dependency reflects the induction of the retroelement by stress. A blood orange of Chinese origin results from an independent insertion of a similar retrotransposon, and color formation in its fruit is also cold dependent. Our results suggest that transposition and recombination of retroelements are likely important sources of variation in Citrus.

The molecular basis for venation patterning of pigmentation and its effect on pollinator attraction in flowers of Antirrhinum.

Pigment stripes associated with veins (venation) is a common flower colour pattern. The molecular genetics and function of venation were investigated in the genus Antirrhinum, in which venation is determined by Venosa (encoding an R2R3MYB transcription factor). Pollinator preferences were measured by field tests with Antirrhinum majus. Venosa function was examined using in situ hybridization and transient overexpression. The origin of the venation trait was examined by molecular phylogenetics. Venation and full-red flower colouration provide a comparable level of advantage for pollinator attraction relative to palely pigmented or white lines. Ectopic expression of Venosa confers pigmentation outside the veins. Venosa transcript is produced only in small areas of the corolla between the veins and the adaxial epidermis. Phylogenetic analyses suggest that venation patterning is an ancestral trait in Antirrhinum. Different accessions of three species with full-red pigmentation with or without venation patterning have been found. Epidermal-specific venation is defined through overlapping expression domains of the MYB (myoblastoma) and bHLH (basic Helix-Loop-Helix) co-regulators of anthocyanin biosynthesis, with the bHLH providing epidermal specificity and Venosa vein specificity. Venation may be the ancestral trait, with full-red pigmentation a derived, polyphyletic trait. Venation patterning is probably not fixed once species evolve full-red floral pigmentation.

A small family of MYB-regulatory genes controls floral pigmentation intensity and patterning in the genus Antirrhinum.

The Rosea1, Rosea2, and Venosa genes encode MYB-related transcription factors active in the flowers of Antirrhinum majus. Analysis of mutant phenotypes shows that these genes control the intensity and pattern of magenta anthocyanin pigmentation in flowers. Despite the structural similarity of these regulatory proteins, they influence the expression of target genes encoding the enzymes of anthocyanin biosynthesis with different specificities. Consequently, they are not equivalent biochemically in their activities. Different species of the genus Antirrhinum, native to Spain and Portugal, show striking differences in their patterns and intensities of floral pigmentation. Differences in anthocyanin pigmentation between at least six species are attributable to variations in the activity of the Rosea and Venosa loci. Set in the context of our understanding of the regulation of anthocyanin production in other genera, the activity of MYB-related genes is probably a primary cause of natural variation in anthocyanin pigmentation in plants.