Abstract
The rate-limiting step of cytokinin biosynthesis pathway is isopentenylation of ATP or ADP, and it is catalyzed by six isopentenyltransferases (AtIPTs) in Arabidopsis. To investigate the roles of AtIPTs for the development of Arabidopsis, we examined the phenotypes of multiple knockouts for AtIPT1, AtIPT3, AtIPT5, AtIPT6, and AtIPT7, which were expressed in vegetative organs. In atipt3,5,6,7 quadruple and atipt1,3,5,6,7 quintuple mutants, the number and length of lateral roots were increased, secondary thickening of roots was reduced, the interval of leaf formation was prolonged, leaf shapes and venations were altered, inflorescence stems were shorter and thinner, the number of axillary buds was reduced. These phenotypes were similar to those of plants overexpressing an cytokinin oxidase/dehydrogenase(AtCKX) gene. Growth of the mutants was partly restored by exogenous cytokinin applications, and it was also restored by transformation with AtIPT3 gene. These results indicate that the mutants phenotypes were caused by reduction in cytokinin biosynthesis.
