title: Cellular localization of the Arabidopsis class 2 phytoglobin influences somatic embryogenesis.
abstract: Mutation of phytoglobin 2 (Pgb2) increases the number of somatic embryos in Arabidopsis. To assess the effects of the cellular localization of Pgb2 on embryo formation, an inducible system expressing a fusion protein consisting of Pgb2 linked to the steroid-binding domain of the rat glucocorticoid receptor (GR) was introduced in a pgb2 mutant line lacking the ability to express Pgb2. In this transgenic system, Pgb2 remains in the cytoplasm but migrates into the nucleus upon exposure to dexamethasone (DEX). Pgb2 retention in the cytoplasm, in the absence of DEX, increased the number of somatic embryos and reduced the expression of MYC2 - an inhibitor of the synthesis of auxin, which is the inductive signal for embryogenesis. Removal of DEX also induced the expression of several genes involved in the biosynthesis of tryptophan and the auxin, indole-3-acetic acid (IAA). These genes included: tryptophan synthase-α subunit (TSA1) and tryptophan synthase-β subunit (TSB1), which are involved in the synthesis of tryptophan, cytochrome P450 CYP79B2 (CYP79B2) and amidase 1 (AMI1), which participate in the formation of IAA via indole-3-acetaldoxime, and several members of the YUCCA family, including YUC1 and 4, which are also required for IAA synthesis. Retention of Pgb2 in the cytoplasm by removal of DEX increased the staining pattern of IAA along the cotyledons of the explants generating embryogenic tissue. Staining for IAA decreased when Pgb2 translocated into the nucleus in response to the application of DEX. Collectively, these results suggest that the presence of Pgb2 in the cytoplasm, but not in the nucleus, phenocopies the effects of Pgb2 mutation in inducing somatic embryogenesis.
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
authors.forename: Cara
authors.initials: C
authors.lastname: Godee
authors.affiliation: Permanent address: Department of Botany, Faculty of Science, Tanta University, Tanta, Egypt 31527.
authors.forename: Mohamed M
authors.initials: MM
authors.lastname: Mira
authors.affiliation: Agriculture and Agri-Food Canada/Government of Canada, Harrow Research and Development Centre, RR #2, 2585 County Rd. 20, Harrow, ON N0R 1G0, Canada.
authors.forename: Owen
authors.initials: O
authors.lastname: Wally
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Hill
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
authors.forename: Claudio
authors.initials: C
authors.lastname: Stasolla
mesh_terms: D017360:Arabidopsis / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D003907:Dexamethasone / Q000008:administration & dosage; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D007210:Indoleacetic Acids / Q000378:metabolism*; D058439:Plant Somatic Embryogenesis Techniques; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C000624491:phytoglobin 2 protein, Arabidopsis; C030737:indoleacetic acid; D003907:Dexamethasone; D014364:Tryptophan
keywords: Auxin; dexamethasone; phytoglobin; somatic embryogenesis.