EXPRESSED SEQUENCE TAGS OF CITRUS-FRUIT DURING RAPID CELL-DEVELOPMENTPHASE

A cDNA library was constructed from satsuma mandarin (Citrus unshiu Ma rc.) fruit tissues during the rapid cell enlargement phase. A total of 950 individual cDNA clones was partially sequenced and compared with GenBank databases for characterizing the gene repertoire expressed dur ing this developmental phase. Among these, 426 cDNA clones (44.8%) sho wed sequence identity with previously characterized genes with optimiz ed (OPT) scores of greater than or equal to 200, while 524 clones (55. 2%) resulted in low OPT scores (<200) and did not show any significant sequence identity with previously published genes. Based on nucleotid e sequence, most clones with OPT scores of greater than or equal to 20 0 were assumed to be transcription-, translation-, cell-wall-metabolis m-, and stress-response-related genes. Other clones showed homology wi th published sequences related to housekeeping and stress-response-rel ated genes, including metallothionein-like proteins, late-embryogenesi s-abundant (LEA) proteins, and heat-shock proteins. These results sugg ested that Citrus fruit during rapid cell enlargement were metabolical ly active and expanding in response to biotic and abiotic stress. For clones with low nucleotide sequence homology, the recurrence was evalu ated by aligning nucleotide sequences of each clone and generating con tig maps. Expressed sequence tags (ESTs) of 162 clones with OPT scores <200 have not been reported for any other organism. Collectively, ran domly sequenced cDNA clones described in this study provided informati on on types of genes expressed during the rapid cell enlargement phase in Citrus fruit. These genes should be used as candidates for Citrus genome mapping projects.