E Larsson

Emma Larsson

Folke Sitbon

J Chandler

Jens Sundström

K Taoka

M Aida

M Furutani

Q Xie

Sara von Arnold

BMC Proceedings

English

PubMed

Springer - Publisher Connector

POSTER PRESENTATION Open Access
NAC regulation of embryo development in
conifers
Emma Larsson*, Folke Sitbon, Jens Sundström, Sara von Arnold
From IUFRO Tree Biotechnology Conference 2011: From Genomes to Integration and Delivery
Arraial d’Ajuda, Bahia, Brazil. 26 June - 2 July 2011
Background
In most gymnosperms the cotyledons develop as a
crown surrounding the incipient shoot apical meristem
(SAM), which maintains the radial symmetry of the
plant throughout embryogenesis. This is in contrast to
the Arabidopsis embryo in which a symmetry-breaking
event (from radial to bilateral symmetry) is associated
with the emergence of the SAM and the two cotyledons
[1]. We have previously shown that the differentiation
of cotyledons and the establishment of the SAM and the
root apical meristem (RAM) in somatic embryos of Nor-
way spruce (Picea abies) is dependent on polar auxin
transport (PAT) [2]. In Arabidopsis PAT restricts the
expression of several genes belonging to the large plant
specific NAC family of transcription factors [3-5], which
in turn induce developmental processes involved in
booth shoot and root formation. Members of the NAC
family have a conserved DNA-binding domain in the N-
terminal region known as the NAC domain, and a more
diverse domain in the C-terminal region, proposed to be
responsible for the trans-activation capacity of the pro-
tein [6]. Despite the diversity of the NAC gene family,
and the importance of NAC proteins in fundamental
processes, no NAC genes have to our knowledge been
characterized in conifers.
Methods
Phylogenetic analyses of NAC domain containing genes
from Picea glauca, Arabidopsisthaliana, Medicago trun-
catula and Physcomitrella patens were performed using
PAUP* and MrBayes. Full-length cDNAs of two NAC
genes were isolated from maturing somatic embryos of
Norway spruce and cloned using standard protocols.
The promoters were amplified using the Genome
Walker™ kit (Clontech). The motif discovery tool
MEME was used to find conserved motifs in the C-
terminal regions and in the promoters of the NAC
sequences from different species. The expression pattern
of the two isolated NAC genes was analyzed in Norway
spruce somatic embryos using quantitative real-time
PCR. Their expression was also analyzed in embryos
that had been treated with the PAT inhibitor NPA as
described earlier [2]. Promoter::GUS fusions were
inserted into embryogenic cultures of Norway spruce
using Agrobacterium mediated transformation.
Results and discussion
We identified several different NAC sequences from
white spruce in GenBank and deployed them to differ-
ent sub-clades within the NAC gene family. Two full-
length cDNAs (gene 1 and gene 2) were cloned from
Norway spruce. Both genes have elements in their pro-
moter region which are significant for specific NAC
genes. Furthermore, gene 1 harbors previously character-
ized motifs that have been shown to have functional
importance in NAC genes in Arabidopsis.
The relative expression of gene 1 increased as early
embryos differentiated, and remained at a high level
until separated cotyledons were clearly visible. However,
the up-regulation was blocked in embryos that formed
fused cotyledons and lacked distinct SAM and RAM
after being treated with NPA. The relative expression of
gene 2 was high in proembryogenic masses and early
differentiating embryos but decreased as the embryos
developed and matured. Interestingly the down-regula-
tion occurred at about the same time as the cotyledons
were delineated. The expression of gene 2 was not
dependent on PAT. Spatial expression analysis using
promoter::GUS fusions revealed that the spruce genes
have specific expression patterns, distinct from the* Correspondence: emma.larsson@vbsg.slu.se
Swedish University of Agricultural Sciences, Department of Plant Biology and
Forest Genetics, PO. Box 7080, 75007 Uppsala, Sweden
Larsson et al. BMC Proceedings 2011, 5(Suppl 7):P67
http://www.biomedcentral.com/1753-6561/5/S7/P67
© 2011 Larsson et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
expression patterns of their most closely related Arabi-
dopsis counterparts.
Conclusion
Taken together, our results show that NAC genes with
distinct signature motifs existed before the separation of
angiosperms and gymnosperms approximately 300 mil-
lion years ago. However, through evolution the expres-
sion of closely related genes has diversified leading to
induction of distinct developmental programs in angios-
perms and gymnosperms.
Published: 13 September 2011
References
1. Chandler J: Cotyledon organogenesis. J Exp Bot 2008, 59:2917-2931.
2. Larsson E, Sitbon F, Ljung K, von Arnold S: Inhibited polar auxin transport
results in aberrant embryo development in Norway spruce. New Phytol
2008, 177:356-366.
3. Aida M, Vernoux X, Furutani M, Traas J, Tasaka M: Roles of PIN-FORMED1
and MONOPTEROS in pattern formation of the apical region of the
Arabidopsis embryo. Development 2002, 129:3965-3974.
4. Furutani M, Vernoux T, Traas J, Kato T, Tasaka M, Aida M: PIN-FORMED1
and PINOID regulate boundary formation and cotyledon development
in Arabidopsis embryogenesis. Development 2004, 131:5021-5030.
5. Xie Q, Frugis G, Colgan D, Chua N-H: Arabidopsis NAC1 transduces auxin
signal downstream of TIR1 to promote lateral root development. Genes
Dev 2000, 14:3024-3036.
6. Taoka K, Yanagimoto Y, Daimon Y, Hibara K, Aida M, Tasaka M: The NAC
domain mediates functional specificity of CUP-SHAPED COTYLEDON
proteins. Plant J 2004, 40:462-473.
doi:10.1186/1753-6561-5-S7-P67
Cite this article as: Larsson et al.: NAC regulation of embryo
development in conifers. BMC Proceedings 2011 5(Suppl 7):P67.
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Larsson et al. BMC Proceedings 2011, 5(Suppl 7):P67
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Page 2 of 2


NAC regulation of embryo development in conifers

Crossref

Cotyledon organogenesis.

Inhibited polar auxin transport results in aberrant embryo development in Norway spruce. New Phytol

M: PIN-FORMED1 and PINOID regulate boundary formation and cotyledon development in Arabidopsis embryogenesis. Development

N-H: Arabidopsis NAC1 transduces auxin signal downstream of TIR1 to promote lateral root development. Genes Dev

The NAC domain mediates functional specificity of CUP-SHAPED COTYLEDON proteins. Plant J

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NAC regulation of embryo development in conifers

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