title: Transcriptional coordination between leaf cell differentiation and chloroplast development established by TCP20 and the subgroup Ib bHLH transcription factors.
abstract: The establishment of the photosynthetic apparatus during chloroplast development creates a high demand for iron as a redox metal. However, iron in too high quantities becomes toxic to the plant, thus plants have evolved a complex network of iron uptake and regulation mechanisms. Here, we examined whether four of the subgroup Ib basic helix-loop-helix transcription factors (bHLH38, bHLH39, bHLH100, bHLH101), previously implicated in iron homeostasis in roots, also play a role in regulating iron metabolism in developing leaves. These transcription factor genes were strongly up-regulated during the transition from cell proliferation to expansion, and thus sink-source transition, in young developing leaves of Arabidopsis thaliana. The four subgroup Ib bHLH genes also showed reduced expression levels in developing leaves of plants treated with norflurazon, indicating their expression was tightly linked to the onset of photosynthetic activity in young leaves. In addition, we provide evidence for a mechanism whereby the transcriptional regulators SAC51 and TCP20 antagonistically regulate the expression of these four subgroup Ib bHLH genes. A loss-of-function mutant analysis also revealed that single mutants of bHLH38, bHLH39, bHLH100, and bHLH101 developed smaller rosettes than wild-type plants in soil. When grown in agar plates with reduced iron concentration, triple bhlh39 bhlh100 bhlh101 mutant plants were smaller than wild-type plants. However, measurements of the iron content in single and multiple subgroup Ib bHLH genes, as well as transcript profiling of iron response genes during early leaf development, do not support a role for bHLH38, bHLH39, bHLH100, and bHLH101 in iron homeostasis during early leaf development.
authors.affiliation: Department of Plant Systems Biology, VIB, Technologiepark 927, 9052, Ghent, Belgium.
authors.forename: Megan E
authors.initials: ME
authors.lastname: Andriankaja
authors.forename: Selahattin
authors.initials: S
authors.lastname: Danisman
authors.forename: Lorin F
authors.initials: LF
authors.lastname: Mignolet-Spruyt
authors.forename: Hannes
authors.initials: H
authors.lastname: Claeys
authors.forename: Irina
authors.initials: I
authors.lastname: Kochanke
authors.forename: Mattias
authors.initials: M
authors.lastname: Vermeersch
authors.forename: Liesbeth
authors.initials: L
authors.lastname: De Milde
authors.forename: Stefanie
authors.initials: S
authors.lastname: De Bodt
authors.forename: Veronique
authors.initials: V
authors.lastname: Storme
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Skirycz
authors.forename: Felix
authors.initials: F
authors.lastname: Maurer
authors.forename: Petra
authors.initials: P
authors.lastname: Bauer
authors.forename: Per
authors.initials: P
authors.lastname: Mühlenbock
authors.forename: Frank
authors.initials: F
authors.lastname: Van Breusegem
authors.forename: Gerco C
authors.initials: GC
authors.lastname: Angenent
authors.forename: Richard G H
authors.initials: RG
authors.lastname: Immink
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002736:Chloroplasts / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D006540:Herbicides / Q000494:pharmacology; D007501:Iron; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000166:cytology* / Q000187:drug effects; D011724:Pyridazines / Q000494:pharmacology; D014026:Nicotiana / Q000166:cytology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D006540:Herbicides; D007501:Iron; D045332:Photosystem II Protein Complex; D011724:Pyridazines; D014157:Transcription Factors; C540502:TCP20 protein, Arabidopsis; C008677:norflurazone