ZmGrp3 is exclusively expressed in epidermal cells of the root-tip and the columella --Woll, K, Hochholdinger, F A full length cDNA of ZmGrp3 (Zea mays Glycine rich protein 3) was isolated in a differential screening of a cDNA-library of maize coleoptilar nodes. Northern-blot analyses showed that ZmGrp3-RNA exclusively accumulates in roots (Goddemeier, M. et al., PMB 36:799-802, 1998). Mutants affected in lateral root (lrt1) (Hochholdinger, F. et al., Plant J. 848- 855, 1998) or crown root initiation (rtcs) (Hetz, W. et al., Plant J. 247-255, 1996) were used to study the root-specific expression of ZmGrp3 in more detail. For lrt1 and its homozygous wild-type siblings RNA from consecutive 2 cm sections of the primary root, beginning at the root-tip, was isolated. In wild-type primary roots, hybridization signals were found in all sections along the whole primary root. However, in primary roots of the lateral-rootless mutant, lrt1, expression of ZmGrp3 was restricted to the first section containing the primary root-tip. For rtcs and its corresponding wild-type siblings, RNA was isolated from coleoptilar nodes. ZmGrp3 expression was detected in wild-type coleoptilar nodes, but not in coleoptilar nodes of the mutant rtcs, which do not form any crown roots (data not shown). These results indicate that ZmGrp3 expression is limited to root-tips.

To support this hypothesis in situ hybridization experiments with root-tissues of the maize inbred line B73 were conducted using a DIG-labeled ZmGrp3-RNA probe. Hybridization signals were observed in epidermal and columella cells of the root-tips in primary, lateral and crown roots at different developmental stages and in the root-tips of embryos 30 days after pollination (Fig. 1). Analyses on protein level, including western-blot analyses and immunolocalization experiments, are in progress.

Figure 1. In situ hybridization of B73 roots with a DIG-labeled ZmGrp3-RNA-probe

A. Lateral root emerging from a primary root; 6 days after germination; longitudinal section; antisense probe
B. Crown root emerging from a coleoptilar node; 5 days after germination; cross section; antisense probe

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