Expression and nucleotide diversity of the maize RIK gene.

The K homology (KH) domain is a conserved sequence present in a wide variety of RNA-binding proteins. The rough sheath2-interacting KH domain (RIK) protein of maize has been implicated in the maintenance of the repressed chromatin state of knox genes during leaf primordia initiation. The amino acid sequences of the publicly available plant RIK proteins contain a splicing factor 1 (SF1)-like KH domain core sequence motif that distinguishes them from all other SF1-like KH domain-containing proteins. We demonstrate that the maize RIK gene exhibits surprisingly little nucleotide sequence diversity among Zea species and subspecies. Microarray hybridization experiments demonstrate that RIK has a higher level of expression in the shoot apical meristem as compared with 14-day seedling. Reverse transcriptase-polymerase chain reaction analysis of RIK indicates that the gene is expressed in many tissues, albeit at lower levels in older leaf samples. Taken together, these data suggest that the RIK protein may be involved in the maintenance of an inactive chromatin state of knox and possibly other genes in nonmeristematic tissues.