An mRNA putatively coding for an O-methyltransferase accumulates preferentially in maize roots and is located predominantly in the region of the endodermis.

ZRP4, a 1.4-kb mRNA that preferentially accumulates in roots of young Zea mays L. plants, was identified by isolation of the corresponding cDNA clone. Genomic Southern analysis indicates that the zrp4 gene is represented once in the corn genome. The deduced ZRP4 polypeptide of 39,558 D is rich in leucine, serine, and alanine. Comparison of the deduced ZRP4 polypeptide sequence to polypeptide sequences of previously cloned plant and animal genes indicates that ZRP4 may be an O-methyltransferase. The ZRP4 mRNA preferentially accumulates in young roots and can be detected only at low levels in leaf, stem, and other shoot organs. ZRP4 mRNA accumulation is developmentally regulated within the root, with very low levels of accumulation in the meristematic region, higher levels in the regions of cell elongation, highest levels in the region of cell maturation, and low levels in the mature regions of the root. ZRP4 mRNA is predominantly located in the endodermis, with lower levels in the exodermis. An intriguing possibility is that the ZRP4 mRNA may code for an O-methyltransferase involved in suberin biosynthesis.