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Published October 1, 2018 | public
Journal Article

Characterization of somatic embryogenesis initiated from the Arabidopsis shoot apex

Abstract

Somatic embryogenesis is one of the best examples of the remarkable developmental plasticity of plants, in which committed somatic cells can dedifferentiate and acquire the ability to form an embryo and regenerate an entire plant. In Arabidopsis thaliana, the shoot apices of young seedlings have been reported as an alternative tissue source for somatic embryos (SEs) besides the widely studied zygotic embryos taken from siliques. Although SE induction from shoots demonstrates the plasticity of plants more clearly than the embryo-to-embryo induction system, the underlying developmental and molecular mechanisms involved are unknown. Here we characterized SE formation from shoot apex explants by establishing a system for time-lapse observation of explants during SE induction. We also established a method to distinguish SE-forming and non-SE-forming explants prior to anatomical SE formation, enabling us to identify distinct transcriptome profiles of these two explants at SE initiation. We show that embryonic fate commitment takes place at day 3 of SE induction and the SE arises directly, not through callus formation, from the base of leaf primordia just beside the shoot apical meristem (SAM), where auxin accumulates and shoot-root polarity is formed. The expression domain of a couple of key developmental genes for the SAM transiently expands at this stage. Our data demonstrate that SE-forming and non-SE-forming explants share mostly the same transcripts except for a limited number of embryonic genes and root genes that might trigger the SE-initiation program. Thus, SE-forming explants possess a mixed identity (SAM, root and embryo) at the time of SE specification.

Additional Information

© 2018 Published by Elsevier Inc. Received 30 November 2017, Revised 16 April 2018, Accepted 24 April 2018, Available online 28 April 2018. We thank K. Boutilier for pLEC1::LEC1-GFP seeds, T. Laux and M. Ueda for pWOX2::WOX2-NLS-YFPx3, W. Werr for DRNp::erGFP seeds, V. A. Grieneisen for pPIN1::PIN1-GFP seeds, C. Ohno for the pWUS::dsRed-N7/PZP222 plasmid, E. M. Meyerowitz for pCLV3::dsRed-N7 seeds, B. Scheres for pWOX5::GFPer seeds and K. Prasad for pDR5rev::3XVENUS-N7/pPIN1::PIN1-GFP seeds. We thank J. Harrison for critical reading and comments on the manuscript, H. Ishihara for advice and assistance on RNA-seq analysis, M. Aida, Y. Jaio and members in Matsunaga's laboratory for valuable comments and discussion. This research was supported by CREST grants from the Japan Science and Technology Agency (JPMJCR13B4) and MXT/JSPS KAKENHI (25113002, 15H05955 and 15H05962) to S.M. We thank Robbie Lewis, MSc, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript. Authors Contributions: SK and KS, Conception and design, Analysis and interpretation of data, Drafting and revising the article; SK, Acquisition of data; PT, Generation of unpublished material; TS, RNA-sequencing; SM, Interpretation of data and revising the article.

Additional details

Created:
August 22, 2023
Modified:
October 18, 2023