Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2004
Publication Date: 7/24/2004
Citation: Li, L., Lu, S., O'Halloran, D.M., Garvin, D.F., Vrebalov, J. 2004. Molecular cloning of or, a novel regulatory gene conferring high level of beta-carotene accumulation in cauliflower [abstract]. American Society of Plant Biologists Annual Meeting. p.88.
Technical Abstract: The cauliflower Or (Orange) gene represents a rare spontaneous carotenoid gene mutation found in plants. It switches on beta-carotene synthesis in many low-pigmented tissues, most noticeably the edible curd, and turns them into orange color. We have undertaken the isolation of Or by a map-based cloning strategy. A 50-kb BAC clone harboring the Or gene was isolated. Sequencing of this BAC clone revealed 15 putative genes. Fine genetic mapping defined a single gene as the candidate for Or. Sequence comparison of the gene from wild type and the Or homozygous mutant uncovered an insertion occurred in one of the exons in the mutant. Database search indicated that this gene encodes a previously uncharacterized protein and shows no sequence homology to any known genes involved in carotenoid biosynthesis. Homologs showing high sequence identity to this candidate gene are present in other plants, including Arabidopsis (>90%) and rice. The Or candidate gene was found to represent a single-copy sequence in the cauliflower genome. It was expressed in the curd, pith and leaf tissues at comparable abundance between wild type and the mutant plant. The transcript of the homolog gene from Arabidopsis was also detected in the aerial parts. The Or candidate protein was predicted for a chloroplast localization, which is being confirmed by GFP-tagged expression. Work is on going to examine the possible nature of this gene mutation (a gain- or loss-of-function). A more detailed biochemical and molecular characterizations of this gene and the gene product are being pursued to shed further light on the mechanisms by which Or regulates beta-carotene accumulation in the plant.