The ICK/KRP cyclin-dependent kinase (CDK) inhibitors are important plant cell cycle factors sharing only limited similarity with the metazoan CIP/KIP family of CDK inhibitors.Little is known about the specific functions of different ICK/KRP genes in planta.In this study, we created double and multiple mutants from five single Arabidopsis ICK/KRP T-DNA mutants, and used a set of 20 lines for the functional investigation of the important gene family.