title: The Transcription Factor ATHB5 Affects GA-Mediated Plasticity in Hypocotyl Cell Growth during Seed Germination.
abstract: Gibberellic acid (GA)-mediated cell expansion initiates the seed-to-seedling transition in plants and is repressed by DELLA proteins. Using digital single-cell analysis, we identified a cellular subdomain within the midhypocotyl, whose expansion drives the final step of this developmental transition under optimal conditions. Using network inference, the transcription factor ATHB5 was identified as a genetic factor whose localized expression promotes GA-mediated expansion specifically within these cells. Both this protein and its putative growth-promoting target EXPANSIN3 are repressed by DELLA, and coregulated at single-cell resolution during seed germination. The cellular domains of hormone sensitivity were explored within the Arabidopsis (Arabidopsis thaliana) embryo by putting seeds under GA-limiting conditions and quantifying cellular growth responses. The middle and upper hypocotyl have a greater requirement for GA to promote cell expansion than the lower embryo axis. Under these conditions, germination was still completed following enhanced growth within the radicle and lower axis. Under GA-limiting conditions, the athb5 mutant did not show a phenotype at the level of seed germination, but it did at a cellular level with reduced cell expansion in the hypocotyl relative to the wild type. These data reveal that the spatiotemporal cell expansion events driving this transition are not determinate, and the conditional use of GA-ATHB5-mediated hypocotyl growth under optimal conditions may be used to optionally support rapid seedling growth. This study demonstrates that multiple genetic and spatiotemporal cell expansion mechanisms underlie the seed to seedling transition in Arabidopsis.
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Petra
authors.initials: P
authors.lastname: Stamm
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Alexander T
authors.identifier: 0000-0002-1175-3556
authors.initials: AT
authors.lastname: Topham
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Nur Karimah
authors.initials: NK
authors.lastname: Mukhtar
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Matthew D B
authors.identifier: 0000-0003-0225-8235
authors.initials: MD
authors.lastname: Jackson
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Daniel F A
authors.initials: DF
authors.lastname: Tomé
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.).
authors.forename: Jim L
authors.identifier: 0000-0002-1855-3215
authors.initials: JL
authors.lastname: Beynon
authors.affiliation: School of Biosciences, College of Life and Environmental and Life Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom (P.S., A.T.T., N.K.M., M.D.B.J., G.W.B); and g.w.bassel@bham.ac.uk.|School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry CV4 7AL, United Kingdom (D.F.A.T., J.L.B.) g.w.bassel@bham.ac.uk.
authors.forename: George W
authors.identifier: 0000-0002-3434-4499
authors.initials: GW
authors.lastname: Bassel
mesh_terms: D016880:Anisotropy; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000235:genetics; D005875:Gibberellins / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D018546:Hypocotyl / Q000166:cytology* / Q000254:growth & development; D030821:Plants, Genetically Modified; D036226:Seedlings / Q000254:growth & development; D012639:Seeds / Q000166:cytology / Q000502:physiology; D059010:Single-Cell Analysis / Q000379:methods; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C473146:ATHB5 protein, Arabidopsis; D029681:Arabidopsis Proteins; C560927:EXPANSIN A7 protein, Arabidopsis; D005875:Gibberellins; D018398:Homeodomain Proteins; D014157:Transcription Factors; C007842:gibberellic acid