Involvement of homeobox genes in early body plan of monocot.

Homeobox genes are known as transcriptional regulators that are involved in various aspects of developmental processes in many organisms. In plants, many types of homeobox genes have been identified, and mutational or expression pattern analyses of these genes have indicated the involvement of several classes of homeobox genes in developmental processes. The fundamental body plan of plants is established during embryogenesis, whereas morphogenetic events in the shoot apical meristem (SAM) continue after embryogenesis. Knotted1-like homeobox genes (knox genes) are preferentially expressed in both the SAM and the immature embryo. Therefore, these genes are considered to be key regulators of plant morphogenesis. In this review, we discuss the regulatory role of knox genes and other types of homeobox genes in SAM establishment during embryogenesis and SAM maintenance after embryogenesis, mainly in rice.