Plant Molecular Biology 37: 377–384, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
A new homeodomain-leucine zipper gene from Arabidopsis thaliana induced
by water stress and abscisic acid treatment
Yong-Hun Lee and Jong-Yoon Chun
Kumho Life and Environmental Science Laboratory, 572 Sangam-Dong, Kwangsan-Gu, Kwangju-City, 506-712,
author for correspondence)
Received 2 June 1997; accepted in revised form 25 January 1998
Key words: abscisic acid, Arabidopsis, homeobox, leucine zipper, water stress
We report the isolation and characterization of a new homeobox gene from Arabidopsisthalianausing a polymerase
chain reaction (PCR) cloning strategy. The full-length cDNA, designated Athb-12, encodes a protein of 235
amino acids. It contains the conserved DNA binding domain and the leucine zipper motif, characteristic of the
homeodomain-leucine zipper family of transcription factors. The deduced amino acid sequence of Athb-12 shows
over 80% identity to the Arabidopsis Athb-7 in the homeodomain (82%) and the leucine zipper motif (80%) of the
proteins. However, outside the homeodomain and the leucinezipper motif,the homology is signiﬁcantly lower.RNA
analysis identiﬁed only one 0.96 kb transcript consistent with the size of Athb-12 cDNA. The Athb-12 transcript
was detected in stem, leaf, ﬂower and root as well as in seedlings. Treatment with water stress and exogenous
abscisic acid (ABA) resulted in the accumulation of Athb-12 mRNA, similar to that of Athb-7.However,thetime
course of the Athb-12 response to ABA differed from that of Athb-7, suggesting that both genes, in response to
ABA, are regulated in different manners. Taken together, these data suggest thatAthb-12 and Athb-7 are members
of a related gene family involved in the plant’s response to water stress.
Homeobox genes have been identiﬁed in several
organisms including various animal species, yeast,
fungi, and higher plants. These genes contain a con-
served sequence motif, the homeobox, that encodes
a sequence-speciﬁc DNA-binding domain known as
the homeodomain (HD) (for a review, see ). In
higher plants, a class of the HD genes was ﬁrst dis-
covered in Arabidopsis thaliana . Unlike other
classic homeobox proteins, the products of these genes
contain a second element that codes for a putative
leucine zipper motif, which is closely linked to the
carboxy-terminal region of the HD. So far, these pro-
teins termed homeodomain-leucine zipper (HD-Zip)
have been identiﬁed only in plants such as sunﬂower
, carrot , soybean , tomato [22, 42], rice
 and Arabidopsis [6, 9, 20, 30–33, 40].
The nucleotide sequence data reported will appear in the EMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession number AF001949.
The uniqueness of the HD-Zip proteins in plants
suggeststhattheseHD-Zip proteins function as a medi-
ator of plant development, for example, coupling of
the developmental response to an environmental sig-
nal . Several lines of evidence support this notion.
Two membersof the HD-Zip family,Arabidopsis Athb-
2 and Athb-4, show a strong increase in mRNA abund-
ance when treated with far-red-rich light [5, 6]. Athb-7
and Athb-8 genes were induced by exogenous plant
hormones such as abscisic acid (ABA) and auxin [1,
29, 39]. ABA is involved in the response of plants
to environmental stresses (for a review, see [23, 37,
38]. For example, treatment with ABA enhances the
resistance of plants to drought , salt , and cold
stress . Several ABA-response genes are induced in
response to drought , salt [25, 41], and cold stress
. A homeobox gene, Athb-7, has been reported to
be induced by drought as well as ABA .