Dividing maize tissues show preferential expression of two novel receptor-like cytoplasmic protein kinases

Two novel members of the receptor-like protein kinase (RLK) family were isolated from maize embryos by homology to ZmPK1, the first RLK identified in the plant kingdom. PK8-a and PK8-b share 88% sequence identity and code for deduced proteins with molecular masses of 57.3 and 56.6 K, respectively. The proteins contain a trans-membrane domain close to the N-terminus and a kinase domain at the C-terminal end. Despite the absence of an extracellular domain they phylogenetically belong to the RLK family where they fall into one of the receptor-like cytoplasmic kinase (RLCK) clades. The RT-PCR and in situ expression profiles reveal an ubiquitous expression with a preference for young, actively dividing tissues and suggest a role in a particular phase of the cell cycle. PK8-a and PK8-b are likely functionally redundant because insertional mutants of PK8-a did not exhibit any major phenotype despite a strong reduction in PK8-a transcript levels.