title: A DELLA in disguise: SPATULA restrains the growth of the developing Arabidopsis seedling.
abstract: The period following seedling emergence is a particularly vulnerable stage in the plant life cycle. In Arabidopsis thaliana, the phytochrome-interacting factor (PIF) subgroup of basic-helix-loop-helix transcription factors has a pivotal role in regulating growth during this early phase, integrating environmental and hormonal signals. We previously showed that SPATULA (SPT), a PIF homolog, regulates seed dormancy. In this article, we establish that unlike PIFs, which mainly promote hypocotyl elongation, SPT is a potent regulator of cotyledon expansion. Here, SPT acts in an analogous manner to the gibberellin-dependent DELLAs, REPRESSOR OF GA1-3 and GIBBERELLIC ACID INSENSITIVE, which restrain cotyledon expansion alongside SPT. However, although DELLAs are not required for SPT action, we demonstrate that SPT is subject to negative regulation by DELLAs. Cross-regulation of SPT by DELLAs ensures that SPT protein levels are limited when DELLAs are abundant but rise following DELLA depletion. This regulation provides a means to prevent excessive growth suppression that would result from the dual activity of SPT and DELLAs, yet maintain growth restraint under DELLA-depleted conditions. We present evidence that SPT and DELLAs regulate common gene targets and illustrate that the balance of SPT and DELLA action depends on light quality signals in the natural environment.
authors.affiliation: School of Biological Sciences, Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH93JH, United Kingdom.
authors.forename: Eve-Marie
authors.initials: EM
authors.lastname: Josse
authors.forename: Yinbo
authors.initials: Y
authors.lastname: Gan
authors.forename: Jordi
authors.initials: J
authors.lastname: Bou-Torrent
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Stewart
authors.forename: Alison D
authors.initials: AD
authors.lastname: Gilday
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Jeffree
authors.forename: Fabián E
authors.initials: FE
authors.lastname: Vaistij
authors.forename: Jaime F
authors.initials: JF
authors.lastname: Martínez-García
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
authors.forename: Ian A
authors.initials: IA
authors.lastname: Graham
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Halliday
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D018548:Cotyledon / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D005875:Gibberellins / Q000494:pharmacology; D018546:Hypocotyl / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D051939:Phytochrome B / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D005875:Gibberellins; D051939:Phytochrome B; D012097:Repressor Proteins; C109555:GAI protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C508468:RGA protein, Arabidopsis; C426006:SPT protein, Arabidopsis; C007842:gibberellic acid