M. Dicristina et al., THE ARABIDOPSIS ATHB-10 (GLABRA2) IS AN HD-ZIP PROTEIN REQUIRED FOR REGULATION OF ROOT HAIR DEVELOPMENT, Plant journal, 10(3), 1996, pp. 393-402
Homeodomain-leucine zipper (HD-Zip) proteins are putative transcriptio
n factors identified only in plants. Related Arabidopsis homeobox gene
s, isolated by virtue of sequence conservation within the helix-3 regi
on of the homeodomain, fall into four families based on sequence simil
arity. This paper reports the characterization of Athb-10, a 747 amino
acid protein belonging to the fourth HD-ZIP family. The studies indic
ate that, although less conserved, the leucine zipper of Athb-10 can f
unctionally replace that of Athb-2 in an in vitro DNA-binding assay. G
ene mapping experiments and sequence comparison analysis revealed that
Athb-10 corresponds to GLABRA2, a homeodomain protein involved in tri
chome development. The mRMA expression analysis revealed that Athb-10/
GLABRA2 is expressed not only in trichome-bearing organs, but also in
the root. The analysis of wild-type and mutant plants showed that the
Athb-10/GLABRA2 gene expression in the aerial part of the plant and in
the root is affected by mutations at the TTG locus. Morphological ana
lysis of the gl2-1 mutant revealed that the gene is necessary not only
for local outgrowth of the trichome, but also for the regulation of r
oot hair development in a subset of epidermal cells. Interestingly, th
e development of root hair cells in a position normally occupied by no
n-hair cells is dependent upon the ethylene regime in which the gl2-1
plants are grown. Sequence analysis of the gl2-1 allele revealed that
the mutant gene encodes a truncated protein that might still retain a
partial activity responsible for the formation of aborted trichomes an
d for the ethylene-dependent regulation of root hair formation.