Maize genes specifically expressed in the outermost cells of root cap

The cells at the periphery of the root cap are continuously sloughed off from the root into the mucilage, and are thought to be programmed to die. By using subtractive hybridization/differential screening and a transmembrane-domain trapping screening strategy involving expression screening in transfected COS-7 cells, we isolated two related maize cDNAs (ZmRCP1 and ZmRCP2) that are specifically expressed in the outermost one to three cells of the cap. ZmRCP1 and ZmRCP2 are homologous proteins of 37 kDa mature polypeptides with a region of regularly-spaced Cys residues and putative N-terminal signal peptides, and represent members of a novel protein family which is conserved among angiosperm and gymnosperm.