Zrp2: a novel maize gene whose mRNA accumulates in the root cortex and mature stems.

A near full-length cDNA clone (pZRP2) was isolated from a cDNA library constructed from maize root mRNAs. The predicted polypeptide has a calculated molecular mass of 66,975 Da, is largely hydrophilic, and contains 26 repeats of a motif the consensus sequence of which is RKATTSYG[S][D/E][D/E][D/E][D/E][P]. The function of the putative protein remains to be elucidated. The ZRP2 mRNA accumulates to the highest levels in young roots, and is also present in mature roots and stems of maize. Further analysis of young roots indicates that the lowest level of ZRP2 mRNA is near the root tip, with relatively high levels throughout the remainder of the root. In situ hybridization reveals that ZRP2 mRNA accumulates predominantly in the cortical parenchyma cells of the root. In vitro nuclear run-on transcription experiments indicate a dramatically higher level of zrp2 gene transcription in 3-day old roots than in 5-day old leaves. A zrp2 genomic clone, which includes the transcribed region and 4.7 kb of upstream sequence, was isolated and characterized.