title: Spatially and genetically distinct control of seed germination by phytochromes A and B.
abstract: Phytochromes phyB and phyA mediate a remarkable developmental switch whereby, early upon seed imbibition, canopy light prevents phyB-dependent germination, whereas later on, it stimulates phyA-dependent germination. Using a seed coat bedding assay where the growth of dissected embryos is monitored under the influence of dissected endosperm, allowing combinatorial use of mutant embryos and endosperm, we show that canopy light specifically inactivates phyB activity in the endosperm to override phyA-dependent signaling in the embryo. This interference involves abscisic acid (ABA) release from the endosperm and distinct spatial activities of phytochrome signaling components. Under the canopy, endospermic ABA opposes phyA signaling through the transcription factor (TF) ABI5, which shares with the TF PIF1 several target genes that negatively regulate germination in the embryo. ABI5 enhances the expression of phytochrome signaling genes PIF1, SOMNUS, GAI, and RGA, but also of ABA and gibberellic acid (GA) metabolic genes. Over time, weaker ABA-dependent responses eventually enable phyA-dependent germination, a distinct type of germination driven solely by embryonic growth.
authors.affiliation: Département de Biologie Végétale, 30, quai Ernest-Ansermet-Sciences III, Université de Genève, 1211 Genève 4, Switzerland.
authors.forename: Keun Pyo
authors.initials: KP
authors.lastname: Lee
authors.forename: Urszula
authors.initials: U
authors.lastname: Piskurewicz
authors.forename: Veronika
authors.initials: V
authors.lastname: Turečková
authors.forename: Solenne
authors.initials: S
authors.lastname: Carat
authors.forename: Richard
authors.initials: R
authors.lastname: Chappuis
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
authors.forename: Luis
authors.initials: L
authors.lastname: Lopez-Molina
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D056625:Endosperm / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018525:Germination; D051942:Phytochrome A / Q000378:metabolism*; D051939:Phytochrome B / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000196:embryology* / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D051942:Phytochrome A; D010937:Plant Growth Regulators; D051939:Phytochrome B; D000040:Abscisic Acid