Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2008
Publication Date: 8/20/2008
Citation: Cuevas, H.E., Staub, J.E., Simon, P.W., McCreight, J.D., Zalapa, J.E. 2008. Mapping of Genetic Loci that Regulate Accumulation of Beta-Carotene in Fruit of U.S. Western Shipping Melon (Cucumis Melo L.) and Their Association With Putative Carotenoid Biosynthesis Genes. Theoretical and Applied Genetics 117:1345-1359.
Interpretive Summary: Carotenoids play indispensable functions in plants. Some carotenoid pigments (e.g. a-carotene, ß-carotene) are also important for human health and nutrition. For instance vitamin A is manufactured in plants using such compounds as a-carotene, ß-carotene. These compounds are found in tomato, pepper, melon, carrots, and wheat. In melon, a-carotene and ß-carotene are found in the fruit. There is an opportunity through traditional plant breeding to increase the amount of these and other carotenes to improve the nutrition of melon. Some carotenes can be observed in melon fruit as an orange color (the higher the orange color the higher the concentation of ß-carotene). Genetic knowledge regarding the inheritance (how genes are transmitted from generation to generantion) about these compounds is critical for effective and efficient plant improvement through breeding. Very little is known about the inheritance of a-carotene and ß-carotene in melon. Thus, a study was undertaken to determine the inheritance of interior fruit color and ß-carotene in melon fruit to allow for the development of improved melon varieties with high carotene content. Melon plants were crossed to produce progeny varing in orange color and ß-carotene. The progeny were assessed for the amount of ß-carotene, and this amount was related to the color of the frut. Several genes (elements of the chromosome that hold genetic information) were identified which control ß-carotene in fruit and are related to the color of the fruit. These genes can now be used to breed higher level of ß-carotene in melon varieties. The information from this study can be used directly by melon breeders to improve their efficiency that in turn will allow for the more rapid development of melon varieties rich in ß-carotene. These high ß-carotene varieties will allow the U.S. grower to be more competitive in the global market place.
Technical Abstract: ßeta–carotene is an important nutrient in the human diet, and melon (Cucumis melo L.) is a key nutritional vegetable source of such carotenoids. A previously developed set of 81 recombinant inbred lines (RIL) derived from Group Cantalupensis U.S. Western Shipper market type germplasm was examined in two locations [Wisconsin (Wisc.) and California (Calif.), USA] for two years to identify quantitative trait loci (QTL) associated with ßeta–carotene accumulation (ßCA) in mature fruit. Three hundred fifty-eight melon simple sequence repeats (SSR), 191 cucumber (Cucumis sativus L.) expressed sequence tag (EST), and 42 cucumber EST-SSR markers were evaluated to enhance saturation of a resident 181-point map. Additionally, genomic information from diverse plant species was used to isolate partial nucleotide sequences of eight putative genes coding for carotenoid biosynthesis enzymes, identify single nucleotide polymorphisms (SNP), and perform candidate gene analysis. Mapping parent analyses detected 64 SSR polymorphisms, seven SNP using cucumber EST and four SNP in putative carotenoid candidate genes, and these markers were used to create a moderately saturated 256-point RIL-based map [104 SSR, 7 CAPS, 4 SNP, 140 dominant markers and one morphological trait (a) spanning 12 linkage groups (LG)] for ßeta–carotene QTL analysis. Eight QTL were detected in this two-location RIL evaluation that were distributed across four LG that explained a significant portion of the associated phenotypic variation for ßCA (R2 = 8 to 31.0%). Broad sense heritabilities for ßCA obtained from RIL grown in Wisc. and Calif. were 0.56 and 0.68, respectively, and 0.62 combining both locations. Although genotypes x environment interactions were confirmed in two-year experiments, relative RIL performance rankings remained consistent. QTL map positions were not uniformly associated with putative carotenoid genes. One QTL (ß-car6.1) interval was located 10 cM from a ß-carotene hydroxylase gene, and this region was colinear with previously reported QTL for color pigmentation. These results suggest that accumulation of ß-carotene in melon is under complex genetic control, where epistasis plays an important role in trait expression. This study provides the initial step for defining the genetic control of ßAC in melon leading to the development of varieties with enhanced ß-carotene content.