A large-scale sequence analysis of rice cDNA was performed for a library from rice callus cultured in a medium containing 1 p.p.m. of 2,4-dichlorophenoxyacetic acid. Random sequencing of 2778 cDNA clones generated 2259 non-redundant expressed sequence tags (ESTs). The strategy of sequencing cDNAs can yield quickly a large number of novel genes. After translation, 690 sequences showed a significant amino acid sequence similarity to sequences already known from PIR. The source of known proteins ranged from bacteria to human. In this report, the non-redundant set of 280 identified ESTs is analyzed in detail.

Endoreduplication is a type of cell cycle in which DNA replication continues without cell division. We have isolated several dominant mutants from Arabidopsis thaliana activation tagging lines by flow cytometry. One of the mutants, increased level of polyploidy1-1D (ilp1-1D), showed increased polyploidy in both light-and dark-grown hypocotyls. The corresponding gene of ilp1-1D encodes a protein homologous to the C-terminal region of mammalian GC binding factor. We demonstrate that this protein functions as a transcriptional repressor in vivo. The expression of all members of the CYCLINA2 (CYCA2) family was reduced in an ILP1 overexpressing line, and the mouse (Mus musculus) homolog of ILP1 repressed cyclin A2 expression in mouse NIH3T3 cells. T-DNA insertion mutants of ILP1 showed reduced polyploidy and upregulated all CYCA2 expression. Furthermore, loss of CYCA2;1 expression induces an increase in polyploidy in Arabidopsis. We demonstrate that this protein regulates endoreduplication through control of CYCA2 expression in Arabidopsis.