Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2003
Publication Date: 6/21/2003
Citation: LI, L., GARVIN, D.F. MOLECULAR MAPPING OF OR, A GENE INDUCING BETA-CAROTENE ACCUMULATION IN CAULIFLOWER (BRASSICA OLERACEA L. VAR. BOTRYTIS). GENOME. 2003. v. 46. p. 588-594. Interpretive Summary: Vitamin A deficiency is a global problem. It is estimated that more than 250 million children worldwide are at risk. As humans are unable to synthesize vitamin A de novo from endogenous isoprenoid precursors, all vitamin A in our foods can ultimately be traced back to a carotenoid origin. To ultimately enhance the nutrition value with increased carotenoid content in plant foods, we need to understand how the carotenoid synthesis and accumulation are regulated in the plant. A cauliflower orange (Or) gene mutation, which induces the accumulation of high levels of B-carotene in various tissues throughout the plant, provides a good model to study these mechanisms. As a first step toward cloning the gene, in this paper, we report on the genetic mapping of this Or gene in the cauliflower genome. We used a high throughput marker search technique to analyze DNA pools from plants containing either the Or gene or the wild type allele. We then identified 10 DNA markers that are physically close to the Or gene in the chromosome and converted them into other forms of markers to facilitate the cloning of this gene. The results presented in this paper are serving as a foundation towards the isolation of this interesting and potentially important Or gene.
Technical Abstract: The cauliflower (Brassica oleracea L. var. botrytis) Or gene, a semi-dominant gene mutation, induces the accumulation of high levels of B-carotene in various tissues that normally are devoid of this pigment. We have previously showed that the Or-induced B-carotene accumulation is not associated with a dramatic increase in the expression of either nonmevalonate or carotenoid biosynthetic genes. Instead, it is associated with the formation of large carotenoid-sequestering structures within the plastids. This Or mutant serves as a good model to study the control of carotenoid accumulation in the plant. As a first step toward the isolation of the Or gene, molecular mapping of this novel gene in cauliflower was undertaken in a mapping population consisting of 195 F2 individuals. By using bulked segregant analysis in conjunction with the amplified fragment length polymorphism (AFLP) technique, 10 AFLP markers tightly linked to the Or gene were identified. Four of the most tightly linked flanking markers were converted into restriction fragment length polymorphism (RFLP) markers. Mapping of these markers in the mapping population placed two of them at 0.5 cM from Or locus on one side, while another marker flanked the Or gene at 1.6 cM on the other side. Three of the markers were also converted into locus-specific PCR-based markers to facilitate high-resolution mapping. These results provide landmarks for the isolation of the Or gene by map-based cloning.