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Expression of a gymnosperm PIN homologous gene correlates with auxin immunolocalization pattern at cotyledon formation and in demarcation of the procambium during Picea abies somatic embryo development and in seedling tissues
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.
Plant Science, University of Manitoba.
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2010 (English)In: Tree Physiology, ISSN 0829-318X, E-ISSN 1758-4469, Vol. 30, no 4, p. 479-489Article in journal (Refereed) Published
Abstract [en]

In seed plants, the body organization is established during embryogenesis and is uniform across gymnosperms and angiosperms, despite differences during early embryogeny. Evidence from angiosperms implicates the plant hormone auxin and its polar transport, mainly established by the PIN family of auxin efflux transporters, in the patterning of embryos. Here, PaPIN1 from Norway spruce (Picea abies [L.] Karst.), a gene widely expressed in conifer tissues and organs, was characterized and its expression and localization patterns were determined with reverse transcription polymerase chain reaction and in situ hybridization during somatic embryo development and in seedlings. PaPIN1 shares the predicted structure of other PIN proteins, but its central hydrophilic loop is longer than most PINs. In phylogenetic analyses, PaPIN1 clusters with Arabidopsis thaliana (L.) Heynh. PIN3, PIN4 and PIN7, but its expression pattern also suggests similarity to PIN1. The PaPIN1 expression signal was high in the protoderm of pre-cotyledonary embryos, but not if embryos were pre-treated with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). This, together with a high auxin immunolocalization signal in this cell layer, suggests a role of PaPIN1 during cotyledon formation. At later stages, high PaPIN1 expression was observed in differentiating procambium, running from the tip of incipient cotyledons down through the embryo axis and to the root apical meristem (RAM), although the mode of RAM specification in conifer embryos differs from that of most angiosperms. Also, the PaPIN1 in situ signal was high in seedling root tips including root cap columella cells. The results thus suggest that PaPIN1 provides an ancient function associated with auxin transport and embryo pattern formation prior to the separation of angiosperms and gymnosperms, in spite of some morphological differences.

Place, publisher, year, edition, pages
Oxford University Press , 2010. Vol. 30, no 4, p. 479-489
Keyword [en]
conifer, embryo patterning, in situ hybridization, meristem, NPA, polar auxin transport (PAT), protoderm, RT-PCR
National Category
Botany
Research subject
Natural Science, Cell and Organism Biology
Identifiers
URN: urn:nbn:se:hik:diva-2928DOI: 10.1093/treephys/tpp126ISI: 000276305100005Scopus ID: 2-s2.0-77950538656OAI: oai:DiVA.org:hik-2928DiVA, id: diva2:300815
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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Publisher's full textScopushttp://treephys.oxfordjournals.org/cgi/reprint/tpp126v1

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Palovaara, JoakimHallberg, HenrikHakman, Inger

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