Why Variation in Flower Color May Help Reproductive Success in the Endangered Australian Orchid Caladenia fulva

Mechanisms of flower coloring and eco-evolutionary implications of massive blooming events in the Atacama Desert

The Atacama Desert, one of the driest places on earth, holds a rich biodiversity that becomes most appreciable in years when unusual rainfall accumulation triggers a phenomenon of explosive development of ephemeral herbaceous and woody desert species known as “desierto florido” or “blooming desert.” Despite the scientific importance of this unique phenomenon only few studies have addressed the mechanisms of flower phenotypic divergence under the fluctuating environment provided by this recurrent event. We investigated the mechanisms of floral color diversity in Cistanthe longiscapa (Montiaceae), a dominant species across the ephemeral blooming landscape of Atacama Desert. Our analyses show that the variation in colors of C. longiscapa flowers result from petals containing betalain pigments with different absorption spectra. The different pigment composition of petals causes flower color differences in the visible and ultraviolet (UV) range of the spectrum. Through color vision models we show that C. longiscapa flowers are highly polymorphic in their color appearance for insect pollinators. Our results highlight the variable nature in flower color of C. longiscapa varieties blooming simultaneously in a geographical restricted area. Given the importance of color in attracting floral visitors, the observed color variability could contribute to increased cross pollination in extreme desert conditions, while accounting for complex and fluctuating histories of plant-pollinator interactions.

Anthocyanin Genes Involved in the Flower Coloration Mechanisms of Cymbidium kanran

The Orchidaceae, otherwise known as orchids, is one of the largest plant families and is renowned for its spectacular flowers and ecological adaptations. Various polymorphisms of orchid flower colour can attract pollinators and be recognised as valuable horticultural ornamentals. As one of the longest historic cultured orchids, Cymbidium kanran has been domesticated for more than 2,500 years and is an ideal species to study coloration mechanisms because of plentiful variations in floral coloration and abundant traditional varieties. In this study, we used two distinct colour-type flowers of C. kanran as experimental materials to elucidate the mechanism of flower coloration. High-performance liquid chromatography (HPLC) analysis revealed that anthocyanins in purple-red-type flowers include three types of anthocyanidin aglycones, peonidin, malvidin, and cyanidin, whereas anthocyanins are lacking in white-type flowers. Through comparative transcriptome sequencing, 102 candidate genes were identified as putative homologues of colour-related genes. Based on comprehensive correlation analysis between colour-related compounds and gene expression profiles, four candidates from 102 captured genes showed a positive correlation with anthocyanidin biosynthesis. Furthermore, transient expression of CkCHS-1, CkDFR, and CkANS by particle bombardment confirmed that recovery of their expression completed the anthocyanin pathway and produced anthocyanin compounds in white-type flowers. Collectively, this study provided a comprehensive transcriptomic dataset for Cymbidium, which significantly facilitate our understanding of the molecular mechanisms of regulating floral pigment accumulation in orchids.