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Comparative expression pattern analysis of WUSCHEL-related homeobox 2 (WOX2) and WOX8⁄9 in developing seeds and somatic embryos of the gymnosperm Picea abies
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Inger Hakman)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Inger Hakman)
Plant Science, University of Manitoba.
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
2010 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 188, no 1, p. 122-135Article in journal (Refereed) Published
Abstract [en]

In seed plants, current knowledge concerning embryonic pattern formation by polar auxin transport (PAT) and WUSCHEL-related homeobox (WOX) gene activity is primarily derived from studies on angiosperms, while less is known about these processes in gymnosperms. In view of the differences in their embryogeny, and the fact that somatic embryogenesis is used for mass propagation of conifers, a better understanding of embryo development is vital.

The expression patterns of PaWOX2 and PaWOX8/9 were followed with quantitative reverse transcription–polymerase chain reaction (qRT-PCR) and in situ hybridization (ISH) during seed and somatic embryo development in Norway spruce (Picea abies), and in somatic embryos treated with the PAT inhibitor N-1-naphthylphthalamic acid (NPA).

Both PaWOX2 and PaWOX8/9 were highly expressed at the early growth stages of zygotic and somatic embryos, and shared a similar expression pattern over the entire embryo. At later embryo stages, high expression of PaWOX8/9 became restricted to cotyledon primordia, epidermis, procambium and root apical meristem (RAM), which became most evident in NPA-treated somatic embryos, while expression of PaWOX2 was much lower.

Our results suggest an ancestral role of WOX in seed plant embryo development, and strengthen the proposed connection between PAT, PIN-FORMED (PIN) and WOX in the regulation of embryo patterning in seed plants.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Place, publisher, year, edition, pages
2010. Vol. 188, no 1, p. 122-135
Keywords [en]
archegonia, conifer, in situ hybridization, N-1-naphthylphthalamic acid (NPA), PCR, polar auxin transport (PAT), rocambium, transcription factor
National Category
Botany
Research subject
Natural Science, Cell and Organism Biology
Identifiers
URN: urn:nbn:se:hik:diva-2929DOI: 10.1111/j.1469-8137.2010.03336.xScopus ID: 2-s2.0-77956295063OAI: oai:DiVA.org:hik-2929DiVA, id: diva2:300817
Available from: 2010-03-01 Created: 2010-03-01 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Conifer embryology: a study of polar auxin transport and WOX transcription factors
Open this publication in new window or tab >>Conifer embryology: a study of polar auxin transport and WOX transcription factors
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plants, like animals, use endogenous signaling molecules to coordinate their own physiology and development. One such molecule in plants is the hormone auxin and recent research has implicated auxin and its polar transport, together with the WOX transcription factors, in regulating embryo patterning and development in angiosperms (flowering plants), the most diverse group of land plants. No extensive investigation of this has been carried out on the more evolutionary distant gymnosperms, the other major taxa of seed plants. Thus, in this thesis I, together with my co-authors, have analyzed the regulation of embryonic pattern formation in the coniferous gymnosperm Picea abies (Norway spruce) using seed and somatic embryos. Conifers are important forestry species and knowledge of their embryology is vital for reforestration programs, where the method of somatic embryogenesis is employed for mass propagation as well as it is used as a model system for embryo development.

Mature spruce embryos display a basic body plan and contain a shoot apical meristem (SAM), cotyledons, hypocotyl, embryonic root and a root apical meristem (RAM), with the meristems generating differentiated cells for organ formation. Treatment of embryos with a polar auxin transport (PAT) inhibitor produce embryos with poor SAM and, in some cases, fused cotyledons. Thus, PAT is essential for the correct patterning of conifer embryos. In angiosperms, PAT is mainly established and maintained by members of the auxin efflux facilitator PIN-FORMED (PIN) family. I isolated a PIN homologue (PaPIN1), of high abundance in conifer tissues, that is localized, together with auxin, to the epidermis of precotyledonary spruce embryos and upregulated as well as delocalized from the epidermis in early PAT inhibited embryos. Since also auxin concentration seems to decrease in the epidermis of these embryos, my data indicate that local auxin accumulation in the epidermis is mediated by PIN-dependent auxin transport.

Further, I investigated WOX genes in conifers and isolated two homologues, PaWOX2 and PaWOX8/9, that are expressed throughout spruce embryo development. Their expression profile suggests involvement in cell proliferation and specification, and, indeed, they both serve as markers for conifer somatic embryogenesis. The expression of PaWOX2 and PaWOX8/9 overlap with PaPIN1 in differentiating vascular tissue (procambium) of spruce embryos and is also upregulated in early PAT inhibited embryos. Thus, PaWOX2, PaWOX8/9, and PaPIN1 may all act together in procambium differentiation. With this, I conclude that a common mechanism, involving PAT and WOX, regulate embryo pattern formation in seed plants. Results in post-embryonic tissue imply a common mechanism regulating pattern formation also here.

Place, publisher, year, edition, pages
Kalmar/Växjö: Linnaeus University Press, 2010
Series
Linnaeus University Dissertations ; 10/2010
National Category
Botany
Research subject
Natural Science, Cell and Organism Biology
Identifiers
urn:nbn:se:hik:diva-2932 (URN)978-91-86491-12-3 (ISBN)
Public defence
2010-04-16, Hörsalen Fullrigaren, Landgången 4, Kalmar, 09:30 (English)
Opponent
Supervisors
Available from: 2010-04-09 Created: 2010-03-01 Last updated: 2014-05-12Bibliographically approved

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Palovaara, JoakimHallberg, HenrikHakman, Inger

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