An upstream region of the Arabidopsis thaliana CDKA;1 (CDC2aAt) gene directs transcription during trichome development

The cell cycle of eukaryotes is tightly regulated through the activity of c yclin-dependent kinases. The Arabidopsis thaliana CDKA;1 (CDC2aAt) gene is thought to encode such a protein kinase, since it is actively transcribed i n proliferating tissues and can complement defects in the Schizosaccharomyc es pombe cdc2 gene. We analyzed the functional structure of the CDKA;1 prom oter, using fusion genes between various upstream regions of CDKA;1 and the Escherichia coli beta -glucuronidase (GUS) gene. A 595 bp DNA fragment ups tream from the transcription start site conferred GUS activity on developin g trichomes, but not on proliferating tissues. On the other hand, another u pstream fragment extending to the 5' non-coding transcribed region gave GUS activity to both proliferating tissues and developing trichomes. Against t he gl2 mutant background, GUS activity directed by the 595 bp fragment was detected in single-stalk cells, but not in giant cells without obvious pola r extension growth. These results revealed that the 595 bp fragment lacks c is element(s) essential for proliferating-cell-specific promoter activity, but can direct transcription in a specific period during trichome developme nt, which does not include cell division. This suggests that CDKA;1 functio ns during cell morphogenesis as well as cell proliferation.