title: Insights into the molecular mechanism of RGL2-mediated inhibition of seed germination in Arabidopsis thaliana.
abstract: BACKGROUND
  Seed germination is of immense significance for agriculture and has been studied for centuries. Yet, our understanding of the molecular mechanisms underlying regulation of dormancy and germination is still in its infancy. Gibberellins are the key phytohormones that promote germination, and the DELLA protein RGL2 is the main signalling intermediate involved in this response. Germination is completely inhibited if functional RGL2 is overexpressed and/or stabilized; however, the molecular mechanisms of RGL2 function are still largely unknown. We therefore attempted to shed light onto some of the genetic events downstream of RGL2.
  
  
  RESULTS
  Gene ontology of the transcriptome differentially regulated by RGL2, as well as extensive cross-comparison with other available microarray data indicates that RGL2-mediated inhibition of germination causes seeds to enter a state of dormancy. RGL2 also appears to differentially regulate a number of transcription factors, many of which are known to be involved in light- or phytohormone-mediated aspects of germination. A promoter analysis of differentially expressed genes identified an enrichment of several motifs that can be bound by specific transcription factors, for example GAMYB, ARF1, or Dof-type zinc fingers. We show that Dof-binding motifs indeed play a role in RGL2-mediated transcription. Using Chromatin Immunoprecipitation (ChIP), we show that RGL2 directly downregulates at least one cell wall modifying enzyme, which is predicted to constrain cell growth thereby leading to inhibition of seed germination.
  
  
  CONCLUSIONS
  Our results reveal that RGL2 controls various aspects of germination. Through the repression of cell wall modifying enzymes, cell growth is directly constrained to inhibit germination. Furthermore, RGL2 likely interacts with various types of proteins to regulate transcription, and differentially regulates several transcription factors. Collectively, our data indicate that gibberellins, acting via RGL2, control several aspects of seed germination.
authors.affiliation: Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore 117543, Singapore.
authors.forename: Petra
authors.initials: P
authors.lastname: Stamm
authors.forename: Pratibha
authors.initials: P
authors.lastname: Ravindran
authors.forename: Bijayalaxmi
authors.initials: B
authors.lastname: Mohanty
authors.forename: Ee Ling
authors.initials: EL
authors.lastname: Tan
authors.forename: Hao
authors.initials: H
authors.lastname: Yu
authors.forename: Prakash P
authors.initials: PP
authors.lastname: Kumar
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018525:Germination; D005875:Gibberellins / Q000378:metabolism / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D057445:Plant Dormancy; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D059467:Transcriptome; D014162:Transfection
chemical_list: C503841:ARF1 protein, Arabidopsis; C473146:ATHB5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D005875:Gibberellins; D018398:Homeodomain Proteins; C450823:RGL2 protein, Arabidopsis; D014157:Transcription Factors; D000040:Abscisic Acid; C007842:gibberellic acid