Flower opening in carnations (Dianthus caryophyllus L.) is the result of the enlargement of petal cells, which requires sugar metabolism. A cDNA encoding sucrose synthase (DcSUS1) was isolated from carnation petals as a candidate gene acting in the initial step of sugar metabolism in petal cells. DcSUS1 transcripts were detected abundantly in floral tissues of flowering carnation plants; the transcripts accumulated most in the petals and style followed by the ovary, whereas only small accumulation were found in stems, leaves, and calyces. Moreover, nearly constant accumulation of DcSUS1 transcripts was found in the petals during flower opening, fully open, and early senescence periods, whereas decreasing accumulation was detected in petals when senescence progressed. These findings suggested the involvement of DcSUS1 expression in petal cell growth during the opening of carnation flowers.
The intron structures of two variants of 1-aminocyclopropane-1-carboxylate synthase (ACS) genes (DcACS1a and DcACS1b) in carnation (Dianthus caryophyllus) and genes homologous to them (ACS1 homologous genes) in other 10 Dianthus species (16 strains in total) were studied by comparing the sizes of the PCR amplificates and nucleotide sequence of the introns. All 16 sequenced homologous ACS1 genes, including DcACS1 genes themselves, had five exons and four introns. The exons had similar nucleotide sequences and consequently similar deduced amino-acid sequences. The sizes of three introns (intron-1, -2, -3) were variable among the homologous genes, whereas that of the fourth intron (intron-4) was almost identical. The variation in introns was probably caused by the insertion (and deletion) of nucleotide fragments of given lengths. Interestingly, the 3'-UTR of DcACS1a was different from that of DcACS1b, and the latter was similar to other 14 ACS1 homologous genes. Moreover, the length of Thr repeat in the C-terminal region was long in DcACS1a protein but short in DcACS1b protein, and the latter resembled ACS1 homologous proteins in other Dianthus species. The present findings suggest that (1) the variation in intron structure between two variants of carnation DcACS1 is reminiscent of the variation that occurred universally in Dianthus species, (2) DcACS1a is probably a gene intrinsic to carnation, and (3) DcACS1b was acquired from another, as yet unknown, Dianthus species, in the course of breeding modern carnation cultivars.
The cuticle, composed of cutin and associated waxes, probably acts as a barrier against water evaporation from the epidermal surface of flower petals. Cuticle formation begins with the biosynthesis of very-long-chain fatty acids (VLCFAs), catalyzed by a fatty acid elongase complex in epidermal cells. In the present study, cDNAs were cloned and analyzed for three enzymes (DcKCR1, DcHCD1, and DcECR1). Combined with the previously obtained cDNA for DcKCS1, the present study completes the identification of cDNAs for the fatty acid elongase complex in 'Light Pink Barbara' carnation for the first time. DcKCS1 transcripts were accumulated at flower opening stage (Os) 2 through Os 6 (full opening stage) with slight changes, but decreased markedly at senescence stage (Ss) 2 and Ss 4. Also, transcripts for DcKCR1, DcHCD1, and DcECR1 were present in considerable amounts during flower opening stages from Os 2 to Os 6. These findings suggested that the expressions of four genes are active during flower opening stage, which is concomitant with the expansion growth in petals requiring rapid formation of a waxy cuticle. Cut flowers of 'Miracle Rouge' carnation have an extremely long vase-life of about three weeks. The cuticle layer on the epidermal cells of 'Miracle Rouge' petals was thinner than that of 'Light Pink Barbara' petals, and 'Miracle Rouge' flowers had a depressed expression of DcKCS1, DcKCR1, and DcHCD1 in petals. These findings suggested that the prolonged vase-life of 'Miracle Rouge' flowers is not related to cuticle formation.
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