REGULATION OF TUBEROUS ROOT FORMATION BY CDK-ACTIVATING KINASE IN SWEET POTATO

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Two cDNAs for a CDK-activating kinase and a cyclin H were cloned and designated Ipoba; CDKD; 1 and Ipoba; CycH; 1, respectively. The deduced amino acid sequences for Ipoba; CDKD; 1 contained an ATP-binding site, an kinase active-site and the conserved threonine residue within the T-loop. The deduced amino acid sequences for Ipoba; CycH; 1 contained N-terminal domain. Ipoba; CDKD; 1 transcript was detected in tuberous roots with the lowest level, although the gene was expressed in allorgans. There was little variety found among the relative abundance of transcripts in different organs. The levels of sucrose, ABA and cytokinins increase in the process of tuberous root formation. Therefore, the effect of these signal molecules on the expression of both Ipoba; CDKD; 1 and Ipoba; CycH; 1. The expression of Ipoba; CDKD; 1 increased by application of sucrose solution, while the expression of Ipoba; CycH; 1 was not significantly affected by sucrose. ABA induced the expression of Ipoba; CDKD; 1, whereas the expression of Ipoba; CycH; 1 was not influenced by ABA. The relative amount of Ipoba; CDKD; 1 mRNA was reduced by benzyladenine, while benzyladenine increased the relative amount of Ipoba; CycH; 1 mRNA. Sucrose antagonized the inhibitory effect of benzyladenine for Ipoba; CDKD; 1 gene expression. Benzyladenine enhanced the expression of Ipoba; CycH; 1 when sucrose was supplemented. These results suggested that cell proliferation was controlled via regulation of CDK-activating kinase and cyclin H gene expression by alterations in the concentration of sucrose, ABA and cytokinin.