OR, A PLASTID PROTEIN, ACCOUNTS FOR THE HIGH LEVEL ACCUMULATION OF BETA-CAROTENE IN CAULIFLOWER

Authors: LU, S. - CORNELL UNIVERSITY; O'HALLORAN, D - CORNELL UNIVERSITY; COSMAN, K - CORNELL UNIVERSITY; Yang, Yong; Xiang, Bosong; Thannhauser, Theodore - Ted; Li, Li

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/16/2005
Publication Date: 7/16/2005
Citation: Lu, S., O'Halloran, D.M., Cosman, K., Yang, Y., Xiang, B., Thannhauser, T.W., Li, L. 2005. Or, a plastid protein, accounts for the high level accumulation of beta-carotene in cauliflower. American Society of Plant Biologists Annual Meeting. p. 606.

Interpretive Summary:

Technical Abstract: The cauliflower (Brassica oleracea L. var. botrytis) Or gene induces carotenogenesis in tissues where carotenoid accumulation is normally repressed. We have isolated the gene representing Or and successfully verified its identity by phenotypic complementation in both cauliflower and Arabidopsis plants. The Or gene encodes a plastid protein with putative transit peptide and transmembrane domains. A transposon insertion after the transit peptide region in the Or gene leads to the orange curd phenotype. Sequencing the cDNA clones from the mutant tissues revealed that the insertion causes alternative splicing events. The Or gene represents a single-copy sequence in the cauliflower genome. The expression of Or gene fluctuates with light/dark shifting in young leaves, showing highest expression around noon. The Or transcript and protein express highly in curd, flower and young leaf tissues. Comparable abundance of mRNA and proteins was observed between wild type and the mutant. Western analysis indicated the removal of the transit peptide after targeting to plastids. By gel filtration and electrophoresis, we found that Or belongs to a protein complex in vivo. Comparative proteomics studies have identified some interesting proteins affected by Or gene mutation in cauliflower and provides information about the metabolic processes associated with carotenogenesis. Or orthologs showing high degree of sequence identity are found in many other species, including Arabidopsis, tomato, potato, maize, and rice, etc., implying a possible broad use of the Or gene to engineer carotenogenesis in some important crops.