Molecular mechanism of ethylene-induced senescence in carnation flowers

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In this research project, we have investigated the molecular mechanism of flowering and senescence of carnation flower, which is a typical ornamental showing ethylene-dependent senescence, and obtained the following results.(1) We revealed several groups of genes which are up- or down-regulated in petal cells during flower opening by a suppressive subtractive hybridization technique. The putative functions of the translational products were classified into several categories including transcription, signaling, cell wall modification, lipid metabolism, and transport. Furthermore, four cDNAs encoding xyloclucantransglucosylase/hy-drolase, three cDNAs encoding expansin and a cDNA encoding sucrose synthase were cloned from petals of opening carnation flowers. Real-time RT-PCR analyses revealed that respective genes are differently expressed during petal development (elongation, expansion and outward-bending), indicating regulated expression of these genes during this process.(2) We revealed the presence of two genes of an ACC synthase (DcACS1), designated as DcACS1a and DcACS1b in the genome of 'Light Pink Barbara' carnation for the first time. They differ mainly in the nucleotide sequences of introns. Moreover, we cloned genomic DNAs of these genes, including their promoter region, and introduced them into tobacco plants. In the near future, it will be possible to see whether these genes will induce climacteric ethylene production in tobacco flowers undergoing senescence.(3) We discovered a gene encoding glycine-rich RNA binding protein (DgGRP1), which has an ethlylene response element (ERE) in its promoter and is down-regulated during carnation flower senescence. This gene will be analyzed in the near future by comparing with cysteine proteinase 1(DcCP1) gene, which has an ERE in its promoter but up-regulated during flower senescence.