Abstract
Somatic embryos of Arabidopsis thaliana can be produced from explants of developing zygotic embryos. Cultivation of explants on maturation medium results in development of three main classes of regenerative structures: adventitious shoots, fused shoots, and complete somatic embryos. The ontogeny and anatomy of these structures was examined using serial plastic sections. Furthermore, two molecular markers were assayed to monitor transcriptional auxin responses and formation of a root meristem in this process: the LENNY allele of PIN4, a transposon insertion creating a fusion to the reporter gene GUS; and DR5::GUS, a synthetic reporter of auxin-induced transcription. In zygotic embryogenesis, PIN4 expression is confined to the center of the root meristem and begins to be detectable by the globular stage of embryogenesis, while DR5::GUS expression marks an “auxin perception maximum” in the more distal regions of the root. Adventitious and fused shoots develop no anatomically recognizable root meristem and do not express either of the two markers at their basal pole. Instead, the vasculature of their axis is directly connected to the vasculature of the explant. By contrast, complete somatic embryos were only loosely attached to the explant, had an anatomically defined root meristem and showed expression of both markers at their root pole. Our results suggest that the establishment of a root meristem in somatic embryos required appropriate auxin levels during the course of their development.
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References
Benková E, Michniewicz M, Sauer M, Teichmann T, Seifertová D, Jürgens G, Friml J (2003) Local, efflux-dependent auxin gradients as a common module for plant organ formation. Cell 115:591–602
Berleth T, Jürgens G (1993) The role of the monopteros gene in organizing the basal body region of the Arabidopsis embryo. Development 118:575–587
Friml J, Benkova E, Blilou I, Wiseniewska J, Hamann T, Ljung K, Woody S, Sandberg G, Scheres B, Jürgens G, Palme K (2002) AtPIN4 mediates sink-driven auxin gradients and root patterning in Arabidopsis. Cell 108:661–673
Friml J, Vieten A, Sauer M, Weijers D, Schwarz H, Hamann T, Offringa R, Jürgens G (2003) Efflux-dependent auxin gradients establish the apical-basal axis of Arabidopsis. Nature 426:147–153
Gaj MD (2001) Direct somatic embryogenesis as a rapid and efficient system for in vitro regeneration of Arabidopsis thaliana. Plant Cell Tiss Org Cult 64:39–46
Gamborg OL, Miller RA, Ojima K (1968) Nutrient requirements of suspension cultures of soybean root cells. Exp Cell Res 50:151–158
Haensch KT (2004) Morph-histological study of somatic embryo-like structures in hypocotyls cultures of Pelargonium × hortorum Bailey. Plant Cell Rep 22:376–381
Halperin W (1995) In vitro embryogenesis: some historical issues and unresolved problems. In: Thorpe TA (ed) In vitro embryogenesis. Kluwer Academic Publishers, Dordrecht, pp 1–16
Hardtke C, Berleth T (1998) The Arabidopsis gene MONOPTEROS encodes a transcription factor mediating embryo axis formation and vascular development. EMBO J 17:1405–1411
Ikeda-Iwai M, Satoh S, Kamada H (2002) Establishment of a reproducible tissue culture system for the induction of Arabidopisis somatic embryos. J Exp Bot 53:1575–1580
Jürgens G (2001) Apical-basal pattern formation in Arabidopsis embryogenesis. EMBO J 20:3609–3616
Komamine A, Murata N, Nomura K (2005) Mechanisms of somatic embryogenesis in carrot suspension cultures–morphology, physiology, biochemistry, and molecular biology. In Vitro Cell Dev Biol-Plant 41:6–10
Leyser O (2005) Auxin distribution and plant pattern formation: how many angels can dance on the point of PIN? Cell 121:819–822
Luo Y, Koop HU (1997) Somatic embryogenesis in cultured immature zygotic embryos and leaf protoplasts of Arabidopsis ecotypes. Planta 202:387–396
Madden JI, Jones CS, Auer CA (2005) Modes of regeneration in Pelargonium × hortorum (Geraniaceae) and three closely related species. In Vitro Cell Dev Biol-Plant 41:37–46
Michalczuk L, Cooke TJM, Cohen JD (1992) Auxin levels at different stages of carrot embryogenesis. Phytochemistry 31:1097–1103
Mordhorst AP, Hartog MV, El Tamer MK, Laux Y, de Vries SC (2002) Somatic embryogenesis from Arabidopsis shoot apical meristem mutants. Planta 214:829–836
Nickle TC, Yeung EC (1994) Further evidence of a role for abscisic acid in conversion of somatic embryos of Daucus carota. In Vitro Cell Dev Biol 30P:96–103
Nomura K, Komamine A (1995) Physiological and biochemical aspects of somatic embryogenesis. In: Thorpe TA (ed) In vitro embryogenesis. Kluwer Academic Publishers, Dordrecht, pp 249–265
Paponov IA, Teale WD, Trebar M, Blilou I, Palme K (2005) The PIN auxin efflux facilitators: evolutionary and functional perspectives. Trends Plant Sci 10:170–177
Pasternak TP, Prinsen E, Ayaydin F, Miskolczi O, Potters G, Asard H, Van Onckelen HA, Dudits D, Feher A (2002) The role of auxin, pH, and stress in the activation of embryogenic cell division in leaf protoplast-derived cells of alfalfa. Plant Physiol 129:1807–1819.
Pillon E, Terzi M, Baldan B, Shiavo FL (1996) A protocol for obtaining embryonic cell lines from Arabidopsis. Plant J 9:573–577
Rech P, Grima-Pettenati J, Jauneau A (2003) Fluorescent microscopy: a powerful technique to detect low GUS activity in vascular tissues. Plant J 33:205–209
Sabatini S, Beis D, Wolkenfelt H, Murfett J, Guilfoyle T, Malamy J, Benfey P, Leyser O, Bechtold N, Weisbeek P, Scheres B (1999) An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root. Cell 99:463–472
Sangwan RS, Bourgeois Y, Dubois F, Sangwan-Norreel BS (1992) In vitro regeneration of Arabidopsis thaliana from cultured zygotic embryos and analysis of regeneration. J Plant Physiol 140:588–595
Steinmann T, Geldner N, Grebe M, Mangold S, Jackson CL, Paris S, Gälweiler L, Palme K, Jürgens G (1999) Coordinated polar localization of auxin efflux carrier PIN1 by GNOM ARF GEF. Science 286:316–318
Sundaresan V, Springer P, Volpe T, Haward S, Jones JD, Dean C, Ma H, Martienssen R (1995) Patterns of gene action in plant development revealed by enhancer trap and gene trap transposable elements. Genes Dev 9:1797–1810
Thorpe TA, Stasolla C (2001) Somatic embryogenesis. In: Bhojwani SS, Soh WY (eds) Current trends in the embryology of angiosperms. Kluwer Academic Publishers, Dordrecht, pp 279–336
Ulmasov T, Murfett J, Hagen G, Guilfoyle TJ (1997) Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements. Plant Cell 9:1963–1971
Vieten A, Vanneste S, Winiewska J, Benková E, Benjamins R, Beeckman T, Luschnig C, Friml J (2005) Functional redundancy of PIN proteins is accompanied by auxin-dependent cross-regulation of PIN expression. Development 132:4521–4531
Yeung EC (1984) Histological and histochemical staining procedures. In: Vasil IK (ed) Cell culture and somatic cell genetics of plants. Academic Press, Orlando, FL, pp 689–697
Yeung EC (1999) The use of histology in the study of plant tissue culture systems–some practical comments. In Vitro Cell Dev Biol-Plant 35:137–143
Yeung EC, Rahman MH, Thorpe TA (1996) Comparative development of zygotic and microspore-derived embryos in Brassica napus L. cv. Topas. I. Histodifferentiation. Int J Plant Sci 157:27–39
Acknowledgments
We would like to thank Professor Trevor Thorpe for a critical reading of the manuscript and to Ms. Stephanie Yeung for her excellent technical assistance in preparing all the histological sections in this study. This research was supported by Discovery grants from the Natural Sciences and Engineering Research Council of Canada to E.C. Yeung.
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Communicated by P. P. Kumar
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Supplementary information Plate 1
Time of root emergence. A, E, and I are a somatic embryo, a fused embryo, and a shoot at the time of detachment. B, F, and J represent the respected structure after 24 hrs of culture; C, G, and K represent their morphology at 48 hrs; and D, H, and L represent their morphology after 72 hrs on the germination medium. All scale bars = 1 mm.
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Bassuner, B.M., Lam, R., Lukowitz, W. et al. Auxin and root initiation in somatic embryos of Arabidopsis . Plant Cell Rep 26, 1–11 (2007). https://doi.org/10.1007/s00299-006-0207-5
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DOI: https://doi.org/10.1007/s00299-006-0207-5