Leafy cotyledon genes are essential for induction of somatic embryogenesis of Arabidopsis
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The capacity for somatic embryogenesis was studied in lec1, lec2 and fus3 mutants of Arabidopsis thaliana (L.) Heynh. It was found that contrary to the response of wild-type cultures, which produced somatic embryos via an efficient, direct process (65–94% of responding explants), lec mutants were strongly impaired in their embryogenic response. Cultures of the mutants formed somatic embryos at a low frequency, ranging from 0.0 to 3.9%. Moreover, somatic embryos were formed from callus tissue through an indirect route in the lec mutants. Total repression of embryogenic potential was observed in double (lec1 lec2, lec1 fus3, lec2 fus3) and triple (fus3 lec1 lec2) mutants. Additionally, mutants were found to exhibit efficient shoot regenerability via organogenesis from root explants. These results provide evidence that, besides their key role in controlling many different aspects of Arabidopsis zygotic embryogenesis, LEC/FUS genes are also essential for in vitro somatic embryogenesis induction. Furthermore, temporal and spatial patterns of auxin distribution during somatic embryogenesis induction were analyzed using transgenic Arabidopsis plants expressing GUS driven by the DR5 promoter. Analysis of data indicated auxin accumulation was rapid in all tissues of the explants of both wild type and the lec2-1 mutant, cultured on somatic embryogenesis induction medium containing 2,4-D. This observation suggests that loss of embryogenic potential in the lec2 mutant in vitro is not related to the distribution of exogenously applied auxin and LEC genes likely function downstream in auxin-induced somatic embryogenesis.
KeywordsArabidopsis Auxin Immature zygotic embryo culture LEC/FUS genes lec/fus mutants Somatic embryogenesis
Immature zygotic embryo
Mature zygotic embryo
Shoot apical meristem
Malgorzata D. Gaj was supported by a Fulbright fellowship. We thank Jennifer Lynn Stonaker (Department of Plant and Microbial Biology, University of California, Berkeley) for help with the establishment of embryogenic cultures, Ling Meng (Department of Plant and Microbial Biology, University of California, Berkeley) for assistance in RT-PCR experiments, Julie Pelletier (Section of Plant Biology, Division of Biological Sciences, University of California, Davis) for maintenance of lec mutants and providing the lec2-1 mutant carrying DR5::GUS construct and Kelly Yee (Section of Plant Biology, Division of Biological Sciences, University of California, Davis) for construction of the double and triple mutants.
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