Cauliflower (Brassica oleraceavar.botrytisL.) curd development: the expression of meristem identity genes

Abstract

Cauliflower homologues to the Arabidopsis genes leafy (Ify) and apetalal (ap1) have been isolated and designated bofh (Ify) and boap1 (ap1). A non-isotopic digoxigenin labelling system was used to visualize these homologues in the developing cauliflower curd. Strong hybridization to antisense riboprobes indicate expression of both bofh and boap1 in all developmental stages, from curd initiation through to petal formation but not in vegetative meristems. The in situ results were supported by Northern and PCR analysis. The data indicate that these two genes are transcribed in the curd meristems, suggesting that cauliflower curd proliferation is not due to bofh or boap1 gene inactivation, but is probably due to negative regulation by a factor/s, indicated by an apparent transcript threshold requirement for each gene prior to floral primordia development. Bofh reaches a peak level at curd maturity. However, boap1 reaches a peak level at pedicel elongation, suggesting that boap1 plays a primary role in specifying conversion of reiterating curd meristems to floral primordia. The differences in the pattern of expression between Arabidopsis and cauliflower is discussed. It is shown that bofh and boap1 transcripts are detectable in apices of photoinduced Brassica campestris L. cv. Ceres, but not in apices of non-induced plants, demonstrating that they are stage-specific in both cauliflower and cv. Ceres. In addition, bofh and boap1 gene expression are affected by temperature, with both genes being switched off during vegetative reversion at high temperatures.