Identification and functional analysis of the ICK gene family in maize

Inhibitors of cyclin-dependent kinases (ICKs) are key regulators of cyclin-dependent kinase activities and cell division. Herein, we identified eight ICKs in maize, which we named Zeama;ICKs (ZmICKs). Primary sequencing and phylogenetic analyses were used to divide the ZmICK family into two classes: group B and group C. Subcellular localization analysis of ZmICK:enhanced green fluorescent protein (eGFP) fusion constructs in tobacco leaf cells indicated that ZmICKs are principally nuclear. Co-localization analysis of the ZmICKs and maize A-type cyclin-dependent kinase (ZmCDKA) was also performed using enhanced green fluorescent protein (eGFP) and red fluorescent protein (RFP) fusion constructs. The ZmICKs and ZmCDKA co-localized in the nucleus. Semi-quantitative RT-PCR analysis of the ZmICKs showed that they were expressed at different levels in all tissues examined and shared similar expression patterns with cell cycle-related genes. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that ZmICK1, ZmICK2, ZmICK3, and ZmICK4 interact with ZmCDKA1 and ZmCDKA3. Interestingly, ZmICK7 interacts with D-type cyclins. Transformed and expressed ZmCDKA1 and ZmICKs together in fission yeast revealed that ZmICK1, ZmICK3, and ZmICK4 can affect ZmCDKA1 function. Moreover, the C-group of ZmICKs could interact with ZmCDKA1 directly and affect ZmCDKA1 function, suggesting that C-group ZmICKs are important for cell division regulation.