Expression based clustering of root development genes in rice, barley and wheat. The heatmap was generated using the mean expression values for the three Triticeae members. The pink color represents higher relative expression and the blue color indicates lower expression. Several of the genes are active only at growing points of primary roots and lateral root initiation sites in Arabidopsis thaliana. The highly localized expression domains were determined using cell-type specific microarray data. The green bars indicate columella root cap expression, while the magenta bar represents epidermis and lateral the root cap. The blue bar represents cortex specific expression.