Senescence in dahlia flowers is regulated by a complex interplay between flower age and floret position

Abstract

Mechanisms regulating flower senescence are not fully understood in any species and are particularly complex in composite flowers. Dahlia (Dahlia pinnata Cav.) florets develop sequentially, hence each composite flower head includes florets of different developmental stages as the whole flower head ages. Moreover, the wide range of available cultivars enables assessment of intraspecific variation. Transcriptomes were compared amongst inner (younger) and outer (older) florets of two flower head ages to assess the effect of floret vs. flower head ageing. More gene expression, including ethylene and cytokinin pathway expression changed between inner and outer florets of older flower heads than between inner florets of younger and older flower heads. Additionally, based on Arabidopsis network analysis, different patterns of co-expressed ethylene response genes were elicited. This suggests that changes occur in young inner florets as the whole flower head ages that are different to ageing florets within a flower head. In some species floral senescence is orchestrated by the plant growth regulator ethylene. However, there is both inter and intra-species variation in its importance. There is a lack of conclusive data regarding ethylene sensitivity in dahlia. Speed of senescence progression, effects of ethylene signalling perturbation, and patterns of ethylene biosynthesis gene expression differed across three dahlia cultivars (‘Sylvia’, ‘Karma Prospero’ and ‘Onesta’) suggesting differences in the role of ethylene in their floral senescence, while effects of exogenous cytokinin were less cultivar-specific.

The genomes of Dahlia pinnata, Cosmos bipinnatus, and Bidens alba in tribe Coreopsideae provide insights into polyploid evolution and inulin biosynthesis

“…D. pinnata and C. bipinnatus are popular flowers all over the world [ 3 , 62 , 63 ], and B. alba is a traditional medical plant, although it is also recognized as an invasive plant [ 60 ]. The genomic resources of D. pinnata and C. bipinnatus presented in this study will promote the studies on regulating mechanisms of flower shapes, colors, and senescence and benefit the flower industry by breeding more popular and long-vase life cultivars of flowers.…”

How far can omics go in unveiling the mechanisms of floral senescence?

“…Transcriptomics is also helping to understand senescence in complex floral architectures such as those of composite chrysanthemums and dahlias [ 39 , 40 ]. These flowers are made up of hundreds of individual florets attached to a central receptacle.…”

“…Floret age increases from the centre of the flower head to the edge, thus floral senescence is a careful coordination of senescence in a gradient across the flower but also temporally as the whole flower head ages. Transcriptomics has shown that 35 different transcription factor families are involved in the regulation of dahlia floret senescence [ 39 ] with most changes in expression seen between inner and outer florets rather than during flower head aging although some are activated in both. However, one of the complications in interpreting these data is in ascribing functions to specific genes since the genome of ornamental dahlias is octoploid, hence there are potentially many different homeologues of each Arabidopsis gene [ 39 ].…”