The cells at the periphery of the root cap are continuously sloughed off fr
om 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 transf
ected 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 polypeptide
s with a region of regularly-spaced Cys residues and putative N-terminal si
gnal peptides, and represent members of a novel protein family which is con
served among angiosperm and gymnosperm.