Characterisation of three ACC synthase gene family members during post-harvest-induced senescence in broccoli (Brassica oleracea L. var. italica)

We investigated the gene expression profiles of different members of the 1-aminocyclopropane-1-carboxilic acid (ACC) synthase (EC 4.4.1.14) gene family in broccoli (Brassica oleracea L. var. italica) during the post-harvest-induced senescence process. Using RT-PCR, three different cDNAs coding for ACC synthase(BROCACS1, BROCACS2 andBROCACS3 were amplified from floret tissue at the start of the senescence process. The three genes share relatively little homology, but have highly homologous sequences inArabidopsis thaliana, and could be functionally related to these counterparts. Southern analyses suggest thatBROCACS1 andBROCACS3 are present as single copy genes, while there are probably two copies ofBROCACS2. All three genes showed different expression patterns:BROCACS1 is likely to be either wound- or mechanical stress-induced showing high transcript levels after harvesting, but no detectable expression afterwards.BROCACS2 shows steady expression throughout senescence, increasing at the latest stages, andBROCACS3 is almost undetectable until the final stages. Our results suggest thatBROCACS1 could be required to initiate the senescence process, whileBROCACS2 would be the main ACC synthase gene involved throughout the post-harvest-induced senescence.BROCACS3’s expression pattern indicates that it is not directly involved in the initial stages of senescence, but in the final remobilization of cellular resources.