Construction of EST library of mixed tissues from maize and analysis of sequences of partial ESTs

With the CLONTEECH vector pDNR-LIB,an EST library of the drought-tolerant maize (Zea mays L.) line YQ7-96 was made from the mixed tissues containing leaves,stems and floral organs at the stage( i.e. up to 12 leaves) of differentiation of the sex organs under normal cultivation without stresses and in the presence of co-stress of water deprivation,salt and alkali for 48 h.This library consisted of over 2×10~5 EST clones,which covered over 4 times of about 50000 genes predicated in the maize genome. The insertion cDNA fragments of 3168 clones selected randomly from the library were sequenced. The total 2098 valid sequences were finally obtained,in which 2002 ESTs were sequenced from 5' end of the cDNAs,96 ESTs were sequenced from 5' and 3' end of the cDNAs. Sequencing results showed that 3' ends of cDNA fragments of all 96 clones sequenced from 3' end had poly A tails. The 2098 valid sequences formed 168 contigs and 1693 singlet,which represented the total 1861 unigenes; Based upon the maize EST database and BLASTn analysis in the GenBank,1731 (93.01%) ESTs had score of or = 100,130 (6.99%) ESTs had score of 100 . This implied that the latter 130 ESTs belonged to sequences of novel genes expressed. 21 ESTs were localized on different chromosomes of maize; The BLASTx analysis showed that in ESTs of 2098 unigenes 1007(48%) ESTs could be functionally annotated,and 1091 (52%)ESTs had no functional information. The above results implied that ESTs in our library would be complementary to the existing maize EST database in the public database.