Control of anthocyanin pigmentation during flower development inCymbidiumorchid

Abstract

The range of flower colours in Cymbidium hybrida orchid is extensive. All three main pigment groups have been detected, but our focus has been on the anthocyanins, which may be present in all sepals and petals, only in the labellum, or as a colour blush. Since anthocyanin pigments have an important influence on final flower colour, it is important to study how their biosynthesis is regulated. We report here the isolation of a MYB transcription factor (ChMYB1) that is shown to be an anthocyanin-related MYB and likely to be part of a regulatory complex controlling anthocyanin biosynthesis in Cymbidium flowers. There are at least two separate phases of anthocyanin development in Cymbidium flowers. One occurs during flower bud development, and the other occurs in open flowers after pollination. The relatively rapid induction of anthocyanin biosynthesis after anther cap removal was used to monitor expression of the MYB1 gene and the flavonoid biosynthetic gene dihydroflavonol 4-reductase (DFR). The involvement of ethylene in this anthocyanin induction was examined by applying the ethylene action inhibitor, 1-methyl-cyclopropene (1-MCP), and by studying the expression of ethylene biosynthesis genes. Expression of the MYB1 gene was first detected 12 h after pollinia removal, and it peaked after 24 h, while expression of the DFR gene was first detected at 24 h after pollinia removal and it peaked after 48 h. 1-MCP treatment abolished completely both anthocyanin accumulation and the expression of the ChMYB1 and ChDFR genes. The results suggest that ChMYB1 regulates in Cymbidium hybrida flowers the pollination-induced anthocyanin production mediated by ethylene signalling.