Plant Molecular Biology 34: 629–641, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
A drought-stress-inducible histone gene in Arabidopsis thaliana is a member
of a distinct class of plant linker histone variants
Robert Ascenzi and J. Stephen Gantt
Department of Plant Biology, University of Minnesota, 1445 Gortner Avenue, St. Paul, MN 55108, USA (
Received 13 December 1996; accepted in revised form 4 April 1997
Key words: linker histone variants, gene family, environmental stress, chromatin, Arabidopsis, abscisic acid
We have isolated and characterized a gene, His1-3, encoding a structurally divergent linker histone in Arabidopsis
thaliana. Southern and northern hybridization data indicate that A. thaliana expresses three single-copy linker
histone genes, each encoding a structurally distinct variant. H1-3 is a considerably smaller protein (167 amino
acids with a mass of 19.0 kDa) than any other described linker histone from higher eukaryotes. We examined
the expression of His1-3 at the RNA and protein levels and found that it is induced speciﬁcally by water stress.
In contrast, expression of His1-1, His1-2 and His4 appear unaffected by water stress. Furthermore, the primary
structure of the protein possesses distinct characteristics that are shared with another drought-inducible linker
histone, H1-D,isolated from Lycopersicon pennellii. Based on structural characteristics of the deduced protein and
its inducible expression, we hypothesize that H1-3 and H1-D are linker histone variants that have specialized roles
in the structure and function of plant chromatin and therefore they can be considered to be members of a unique
subclass of plant histones. Immunoblottingwith an antibody produced against a short polypeptide in the conserved
domain of this subtype indicates that similar proteins may exist in other plants.
Regulated gene expression is required for a variety of
developmental and physiological processes in plants.
Transcriptionalregulationis dependent not only on the
speciﬁc interactions between transcription factors and
the promoter elements to which they bind, but also on
the local and regional chromatin environment of genes
[5, 58]. It has been shown that the binding of trans-
acting factors to their cis elements is inhibited in nuc-
leosomal DNA as compared to naked DNA, and vari-
ous mechanisms of alleviating nucleosomal repression
have been described (reviewed in ). Most notably,
large protein complexes such as SWI/SNF and NURF,
have recently been described and shown to be required
for the energy-dependent disruption of nucleosomes
(reviewed in ).
GenBank and DDBJ Nucleotide Sequence Databases under the
accession numbers U73781 (cDNA) and U72241 (gene).
Chromatin does not appear to be globally homo-
genous. A variety of studies have provided evidence
that the composition of nucleosomes and binding of
non-histone chromatin proteins may have an inﬂuence
on the transcriptional potential of genes [30, 45, 52].
Variation in chromatin structure can be brought about
by the incorporation of non-histoneproteins as well as
the substitution of distinct histone variants [12, 22, 48]
Histone variants have long been studied in plants
(reviewed in ). The most variablehistonein plants,
as well as other eukaryotes, is the linker histone (e.g.
, H5). Unlike the core histones (H4, H3,
H2A, H2B), this lysine-rich family of proteins binds
to the external surface of nucleosomes, linking adja-
cent nucleosomes.Chromosomecondensationprior to
cesses that have been attributedto linker histones [1, 2,
44]. All plant and animal linker histones described to
GR: 201001958, Pips nr. 138691 BIO2KAP
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