Using transcriptomics to identify gene markers for flower longevity in dahlias

Floral longevity is a key feature of importance to cut flowers, however, its regulation is not fully understood especially in composite flowers such as dahlias (Dahlia spp.). Understanding how floral longevity is regulated could help to devise new strategies for reducing waste in the supply chain for cut flowers. Dahlia flowers are composed of whorls of florets within a capitulum or flower head, which develop sequentially such that inner florets are physiologically younger than the older florets at the margins. Hence, within a single flower head, a range of floret ages are represented. How the senescence of the different florets is coordinated is of fundamental interest but is also important as the deterioration of the outermost florets determines vase life of the whole flower. Thus, dahlia flower heads can be staged sequentially from the bud stage through opening of the majority of the florets to the sequential senescence of the floret whorls. In some flowers of some species, ethylene is an important regulator of longevity but in others it is not. In dahlia the role of ethylene varies across different cultivars suggesting the involvement of other plant hormones in the control of longevity. Transcriptomics is a powerful technique for revealing important genes and pathways that may regulate developmental processes, especially in species for which there is no genome sequence and few genetic resources. A transcriptomic analysis of Dahlia pinnata ‘Sylvia’ revealed that the expression of hundreds of genes differs both between outer and inner florets on the same flower head but also between inner florets on flower heads of different ages, suggesting a complex regulation of floret development. Abscisic acid (ABA) is known to accumulate during floral senescence in some species and in dahlia the expression of ABA related genes was assessed in the transcriptome analysis showing that genes encoding proteins involved both in biosynthesis and response to ABA altered in expression during floret senescence, suggesting a complex role of this plant hormone.