A PAPAYA BAC LIBRARY AS A FOUNDATION FOR MOLECULAR DISSECTION OF A TREE-FRUIT GENOME

¹ Hawaiian Agricultural Research Center, Aiea, HI 96701

² Dept Soil and Crop Science, Texas A&M University, College Station, TX 77843

³ USDA-ARS, National Clonal Germplasm Repository, Hilo, HI 96720

⁴ USDA-ARS, Tropical Fruit, Vegetable & Sugarcane Research Unit, Aiea, HI 96701

⁵ Applied Genetic Technology Center, University of Georgia, Athens, GA 30602

Because of its relatively small genome (379 Mbp/1C) and ability to produce ripe fruit 10 to 12 months after planting, papaya (Carica papaya L.) can be a model plant for studying genes that affect fruit characters. A rapid approach to locating fruit-controlling genes is to assemble a physical map based on BAC contigs on which ESTs have hybridized. We report constructing a papaya BAC library as a first step towards this goal. Our BAC library consists of 39,168 clones from two separate ligation reactions with DNA from the cultivar "SunUp". The average insert size of the library is 132kb. 94.3% of the 18,700 clones from the first ligation contained inserts that averaged 86 kb in size. 96.7% of the 20,468 clones from the second ligation contained inserts that averaged 174 kb in size. Two sorghum chloroplast probes hybridized separately to the library revealed a total of 504 chloroplast clones or 1.3% of the library. A cotton rDNA probe hybridized to 61 BACs or 0.16% of the library. Thus, our BAC library was estimated to cover 13x of the papaya genome excluding the false positive, chloroplast, and rDNA clones. Eleven papaya cDNA and ten Arabidopsis cDNA probes detected an average of 18.9 and 27.0 BACs, respectively. This BAC library will be used for papaya gene cloning and physical mapping. A physical map of the papaya genome will significantly enhance the capacity to clone and manipulate genes of economic importance.