Orange cauliflower was first discovered around thirty years ago, when it was found to be growing alongside white cauliflower in a farmer's field. At the end of last year Cornell plant geneticist Li Li and colleagues reported in the journal Plant Cell that they had isolated the genetic mutation responsible for the colour. In fact, the colour is attributed to higher levels of the vitamin A precursor beta carotene. While cauliflower and other staple crops are able to synthesise beta-carotene, they are limited in their ability to store it as they do not have a "metabolic sink". Li, in collaboration with Joyec Van Eck of Cornell's Boyce Thompson Institute for Plant Research, is currently applying the discovery to potatoes, altering their genes to increase the metabolic sink and beta-carotene synthesis.
While details of the ongoing work are not yet available, Li said: "The research provides a possible new technique for genetically-modifying staple crops to increase their ability to store beta-carotene and increase nutritional content." Vitamin A and its precursor is particularly important in crops since deficiency of the nutrient is rife in developing countries, and is the leading cause of blindness in children. Li's original cauliflower discovery was based on positional cloning, which allowed them to isolate the gene, dubbed 'Orange'. Orange appears to be plant-specific, and to be highly conserved among divergent plant species.
"Analyses of the gene, the gene product, and cytological effects of the Orange transgene suggest that the functional role of Orange is associated with a cellular process that triggers the differentiation of proplastids or other noncoloured plastids into chromoplasts for carotenoid accumulation," wrote Li. This is not the first time genes have been inserted into a crop to boost its beta-carotene capacity. For instance, Syngenta has led the way in a transgenic beta carotene-rich rice, called Golden Rice. In 2005 it launched a new version, Golden Rice II, which is said to produce up to 23-times more provitamin A nutrients than the original, giving it a maximum carotenoid level of 37 micrograms per gram of rice and a preferential accumulation of beta-carotene. Important as this work is, especially given the role of rice as one of the world's most-consumed staples, Li and colleagues said that the technique has proved less effective in many other plants.
Their technique is said to offer a potential alternative and complementary technique for bolstering the nutritional value of a broader selection of staple crops. Source: Plant Cell First published online December 15, 2006. Doi: 10.1105/tpc.106.046417 "The cauliflower Or gene encodes a DnaJ Cysteine-rich domain-containing protein that mediates high levels of beta-carotene."
Authors: Shan Lu, Joyce Van Eck, Xiangjun Zhou, Alex B Lopez, Diana M O'Halloran, Kelly M. Cosman, Brian J Conlin, Dominick J Paolillo, David F Garvin, Julia Vrebalov, Leon V Kochian, Hendrik Küpper, Elizabeth D Earle, Jun Cao and Li Li.