Submitted to: Genetics and Molecular Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2004
Publication Date: 4/1/2005
Citation: Santos, C.A., Senalik, D.A., Simon, P.W. 2005. Path analysis suggests phytoene accumulation as the key step limiting the carotenoid pathway in roots of white carrot. Genetics and Molecular Biology. 28:287-293. Interpretive Summary: The carotenoids are orange, red, and yellow pigments important for both plant survival and human health, and they impart the familiar orange color of carrots. To understand the biosynthesis of carrot carotenoids we nused a mathematical method, called path analysis. The biosynthetic pathway deduced with this method was identical to that deduced by other researchers using genetic methods. This research is of interest to plant biochemists and geneticists studying biosynthesis.
Technical Abstract: To understand intrinsic factors limiting carotenoid accumulation in carrots, relationships among major root carotenes, root color, and several carrot morphological traits were studied in two F2 populations of carrot (Daucus carota L.), with very unrelated genetic backgrounds, by applying phenotypic correlations and path analysis. Most correlations among characters were close and concordant in signal between the two populations. Root weight had moderate to highly significant positive correlation with leaf length, root length and top and middle root diameter. Total dissolved solids trait was weakly correlated with root color and carotenes and was negatively correlated with all morphological characters. Phenotypic correlations failed to identify the order of substrates and products of the carotenoid pathway. However, the correct order of substrates and products, phytoene to zeta-carotene to lycopene, was identified in the causal diagram of beta-carotene in the cross Brasilia (orange roots) x HCM (very dark orange). Path analysis of beta-carotene, in the cultivated B493 (dark orange) x wild carrot QAL (white) cross, suggested that selection for root carotenes had little effect on plant morphological traits. A causal model of beta-carotene and lycopene in this cross suggested that phytoene synthesis is the key step limiting the carotenoid pathway in white carrots. Path analysis, first presented by Sewall Wright to study quantitative traits, appears as a powerful statistical approach to identify key compounds of a complex pathway.