RANDOM SEQUENCING OF SWEET ORANGE (CITRUS-SINENSIS OSBECK) CDNA LIBRARY DERIVED FROM YOUNG SEEDS

Sequencing of randomly selected cDNA clones was carried out to survey the repertoire of genes expressed in immature seeds of 'Valencia' oran ge (Citrus sinensis Osbeck) and to produce restriciton fragment length polymorphism (RFLP) markers on the genome mapping program in Citrus. A cDNA library was made by using mRNA prepared from immature seeds of 'Valencia' orange whose developing embryos were at an early globular s tage. A total of 192 individual cDNA clones were partially sequenced a nd compared with the GenBank database. The cDNA clones, which presente d significant homology to previously characterized plant, eukaryote, a nd all other organism genes (optimized (OPT) score > 200) in data sour ce formed 24.5 % (47 clones), 12.0 % (23 clones) and 8.8 % (17 clones) of total cDNA clones analyzed in this experiment. The seed cDNA libra ry showed low level of redundancy of cDNA clones. Some clones such as metallothionein, however, were revealed several times, suggesting poss ible isoforms, Although putative genes, which are thought to play a ro le on embryogenesis, were not screened in this experiment, a wide rang e of genes involved in functions such as metabolism, translation, sign al transduction, and stress responses were obtained. The randomly sequ enced cDNA clones described in this study provide, for the first time, an indication of the types of genes expressed at an early stage of se ed development in Citrus. Furthermore, this method made possible the s election of many gene species which could be used as RFLP probes.