Gene Expression Analysis of <i>NAC</i> Transcription Factors Related to Flower Senescence in <i>Dahlia</i>

Dahlia (Dahlia variabilis) flowers exhibit wide variety in terms of color, shape, and size; however, their short vase life limits their utility as ornamental plants. This study aimed to identify candidate genes related to flower senescence in dahlia using RNA-seq analysis. In total, 2,698 transcription factors were identified in dahlia flowers, with 114 genes belonging to the NAC family. Additionally, FPKM levels of five NAC transcription factors (DvNAC1, DvNAC2, DvNAC3, DvNAC4, and DvNAC5) increased from flowering to senescence (petal wilting) in the dahlia ‘Kamakura’. Therefore, the expression level of these NACs was investigated in three dahlia cultivars ‘Kamakura’, ‘Micchan’ and ‘Port Light Pair Beauty’ by real-time PCR. The expression level of all five NACs increased from flowering to flower senescence in the three cultivars. The increase in DvNAC1, DvNAC2, DvNAC3, and DvNAC5 expression was delayed in ‘Micchan’ compared to that in ‘Kamakura’ and ‘Port Light Pair Beauty’. This delay in DvNAC1, DvNAC2, DvNAC3, and DvNAC5 expression corresponded with ‘Micchan’ having a longer vase life than the other two cultivars. Furthermore, ethylene treatment accelerated flower senescence and increased NACs expression, except for DvNAC4, while 1-methylcyclopropene delayed both flower senescence and the increase in NAC expression in the three cultivars. These results indicate that NAC transcription factors, especially DvNAC1, DvNAC2, DvNAC3, and DvNAC5, are likely to be genes associated with flower senescence in dahlia.