Joint Research on Differentiation and Growth specificity of Plant Cells

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(1)S phase-specific and auxin-enhanced activation or telomerase was demonstrated using cell-extract of cynchronized tobacco culture cells. Genes (cDNAs) for the catalytic subunits of Arabidopsis thallana and Oryza sativa (AtFERT and OsTERT) were cloned for the first time from higher plants. Highest ArTERT expression in the apical meristems was verified using northern and in situ hybridization. (2) A proteinaceous fraction having an inhibitory activity against telomerase was found in plant cell extracts. A 40 kDa protein presumably involved in the regulation of telomerase activity was identified. (3) Genes (cDNAs) for Ku70 and Ku80 homologs of Arabidopsis thaliana (AtKu70 and AtKu80) were cloned and sequenced. A heterodimer specifically formed between purified AtKu70 and AtKu80 proteins revealed sDNA-dependent ATPase and ATP-dependent DNA helicase as well as specific binding to double-stranded DNA ends. DSBs (double-strand breaks) by bleomycin or MMS treatment of cultured cells induce the expression of these genes. (4) Six genes for the nuclear-encoded plastid sigma factors of Arabidopsis thaliana (originally named SIGA〜SIGF and later renamed SIGI〜SIG6, respectively) were identified. A T-DNA inserted mutant (sig 2-1) in SIG2 (SIGB) gene having pale-green phenotype was isolated. Several plastid-encoded tRNAs including trnE-UUC indispensable for chiorophyII (tetrapyrrole) biosynthesis in plants were drastically reduced but that some tRNAs were not affected so much by the SIG2-deficiency.