Construction and characterization of a normalized whole-life-cycle cDNA library of rice

A cDNA library with genomic complete coverage is a powerful tool for functional genomic studies. For studying the functions of rice genes on a large scale, a normalized whole-life-cycle cDNA library is constructed based on the strategy of saturation hybridization with genomic DNA using rice cultivar Minghui 63, an elite restorer line for a number of rice hybrids that are widely cultivated in China. This library consists of cDNA from 15 directionally cloned cDNA libraries constructed with different tissues from 9 developmental stages. For normalization, the denatured plasmids purified front the 15 directionally cloned libraries are mixed and hybridized with saturated genomic DNA labeled with magnetic beads in two complementary systems. Well-matched plasmids are captured from the hybridized genomic DNA and electroporated into competent DH10B E. coli for construction of the normalized whole-life-cycle cDNA library. This library consists of 62000 clones with an average insert length about 1.4 kb. Inverse Northern blotting shows that this cDNA library included many rarely expressed genes and tissue-specific genes. Sequencing of 10750 cDNA clones of this library reveals 6399 unique ESTs (expressed sequence tags), indicating that the non-redundancy of the library is about 59.5%. This library has been used to make cDNA microarrays for functional genomic studies.