Download A Histone Chaperone and a Specific Transcription

The Plant Cell, Vol. 29: 197–198, February 2017, www.plantcell.org ã 2017 American Society of Plant Biologists. All rights reserved.
IN BRIEF
A Histone Chaperone and a Specific Transcription Factor Modulate
GLABRA2 Expression in Root Hair Development
OPEN
To navigate its essential function of producing mRNAs, RNA polymerase II (Pol II) must
navigate the thread of DNA, which winds
around thousands of nucleosomes. If you’ve
ever tried to use a sewing machine but got
your bobbin thread tangled, then the task
faced by Pol II may seem impossible. However, Pol II has help: Histone chaperones
and chromatin-remodeling complexes remove nucleosomes from its path; they also
slide nucleosomes, prevent the aggregation
of free histones with DNA, and exchange
nucleosomes with histone variants (reviewed
in Venkatesh and Workman, 2015). Some
chaperones interact preferentially with different histones; for example, H2A/H2B chaperone interact with the H2A/H2B dimers that
flank the (H3-H4)2 tetramer in the histone
core.
Histone chaperones affect transcription,
DNA replication, and DNA repair and play
important roles in plant growth and development (reviewed in Zhou et al., 2015).
For example, mutants of the histone H2A/
H2B chaperone genes NUCLEOSOME ASSEMBLY PROTEIN1-RELATED PROTEIN1
(NRP1) and NRP2 produce ectopic root
hairs. Root hairs develop from single epidermal cells (H-cells). In Arabidopsis thaliana, H-cells develops over the junctions
between pairs of cortical cells; epidermal cells not directly over the junction
(N-cells) do not generally form root hairs.
The homeodomain-leucine zipper transcription factor GLABRA2 (GL2) suppresses
formation of root hairs in N-cells, and root
hair specification involves changes in GL2
transcription. Zhu et al. (2017) examined
the role of NRP1 and NRP2 in root hair
development and found that the nrp1-1
nrp2-1 mutants have lower GL2 expression, although GL expression occurs in
the same cells (see figure).
The basic helix-loop-helix transcription
factor WEREWOLF (WER) forms part of a
complex that activates GL2 expression in
OPEN
Articles can be viewed without a subscription.
www.plantcell.org/cgi/doi/10.1105/tpc.17.00131
Expression of GL2 in roots. Expression of the GL2:GUS reporter construct in the N-cells of root tips
(top; bar 5 50 mm) and cross sections (bottom; bar 5 20 mm) of wild-type (WT) and nrp1-1 nrp2-1
mutant roots. (Reprinted from Zhu et al. [2017], Figure 1.)
N-cells, and the transcript levels of WER and
other upstream regulators of GL2 remained
unchanged in the nrp1-1 nrp2-1 mutants.
Also, the wer-1 nrp1-1 nrp2-1 triple mutants
had more root hairs than the nrp1-1 nrp2-1
double mutants, similar to the wer-1 single
mutants, suggesting that wer-1 is epistatic.
The authors next used chromatin immunoprecipitation-PCR to show that association
of NRP1 with the GL2 promoter decreased
significantly in the wer-1 mutants. Pull-down
and bimolecular fluorescence complementation assays showed that WER and NRP1
directly interact; size-exclusion chromatography indicated that WER and NRP1 form
a 1:1 complex and that NRP1 forms dimers.
Indeed, determination of the crystal structure
of NRP1 showed that NRP1 forms dimers
through an N-terminal a-helix. Mutations
that disrupt the ability of NRP1 to form
dimers and mutants that disrupt its acidic
C terminus decrease NPR1’s interaction
with histones and with WER1. Moreover,
these mutants do not rescue the nrp1-1
nrp2-1 phenotype.
These results linked the NRP1 and NRP2
histone chaperones with WER; the authors
next explored how these factors affect
chromatin structure at GL2. They found
that the GL2 promoter had higher histone
occupancy and nucleosome density (and
was less accessible to micrococcal nuclease) in the nrp1-1 nrp2-1 mutants than in the
wild type. Other loci, such as ACTIN2 and
FLOWERING LOCUS C, did not show a difference between the mutant and wild type.
Finally, electrophoretic mobility shift assays
showed that the presence of histones decreased binding of WER to its target, but
NRP1 removed the histones and allowed
WER to bind.
This study used a wide-range of techniques, including genetics, molecular biology, and crystallography, to examine how
the interaction of histone chaperones with
the WER transcription factor targets these
chaperones to GL2 and alters the chromatin
there. Determining how generally this mechanism occurs, what other chromatin factors
affect GL2, and how NRPs regulate other
198
The Plant Cell
loci will provide intriguing topics for future
work.
Jennifer Mach
Science Editor
[email protected]
ORCID ID: 0000-0002-1141-6306
REFERENCES
Venkatesh, S., and Workman, J.L. (2015).
Histone exchange, chromatin structure, and
the regulation of transcription. Nat. Rev. Mol.
Cell Biol. 16: 178–189.
Zhou, W., Zhu, Y., Dong, A., and Shen, W.H.
(2015). Histone H2A/H2B chaperones: from
molecules to chromatin-based functions in
plant growth and development. Plant J. 83:
78–95.
Zhu, Y., Rong, L., Luo, Q., Wang, B., Zhou, N.,
Yang, Y., Zhang, C., Feng, H., Zheng, L.,
Shen, W.-H., Ma, J., and Dong, A. (2017).
The histone chaperone NRP1 interacts with
WEREWOLF to activate GLABRA2 in Arabidopsis root hair development. Plant Cell 29:
260–276.
A Histone Chaperone and a Specific Transcription Factor Modulate GLABRA2 Expression in
Root Hair Development
Jennifer Mach
Plant Cell 2017;29;197-198; originally published online February 17, 2017;
DOI 10.1105/tpc.17.00131
This information is current as of June 18, 2017
Supplemental Data
/content/suppl/2017/02/21/tpc.17.00131.DC1.html
References
This article cites 3 articles, 1 of which can be accessed free at:
/content/29/2/197.full.html#ref-list-1
Permissions
https://www.copyright.com/ccc/openurl.do?sid=pd_hw1532298X&issn=1532298X&WT.mc_id=pd_hw1532298X
eTOCs
Sign up for eTOCs at:
http://www.plantcell.org/cgi/alerts/ctmain
CiteTrack Alerts
Sign up for CiteTrack Alerts at:
http://www.plantcell.org/cgi/alerts/ctmain
Subscription Information
Subscription Information for The Plant Cell and Plant Physiology is available at:
http://www.aspb.org/publications/subscriptions.cfm
© American Society of Plant Biologists
ADVANCING THE SCIENCE OF PLANT BIOLOGY