Fluorescent reporter lines for auxin and cytokinin signalling in barley (Hordeum vulgare)

PLoS One. 2018 Apr 25;13(4):e0196086. doi: 10.1371/journal.pone.0196086. eCollection 2018.

Abstract

The phytohormones auxin and cytokinin control development and maintenance of plant meristems and stem cell systems. Fluorescent protein reporter lines that monitor phytohormone controlled gene expression programmes have been widely used to study development and differentiation in the model species Arabidopsis, but equivalent tools are still missing for the majority of crop species. Barley (Hordeum vulgare) is the fourth most abundant cereal crop plant, but knowledge on these important phytohormones in regard to the barley root and shoot stem cell niches is still negligible. We have now analysed the role of auxin and cytokinin in barley root meristem development, and present fluorescent protein reporter lines that allow to dissect auxin and cytokinin signalling outputs in vivo. We found that application of either auxin or cytokinin to barley seedlings negatively impacts root meristem growth. We further established a barley cytokinin reporter, TCSnew, which revealed significant cytokinin signalling in the stele cells proximal to the QC, and in the differentiated root cap cells. Application of exogenous cytokinin activated signalling in the root stem cell niche. Commonly employed auxin reporters DR5 or DR5v2 failed to respond to auxin in barley. However, analysis of putative auxin signalling targets barley PLETHORA1 (HvPLT1) is expressed in a similar pattern as its orthologue AtPLT1 from Arabidopsis, i.e. in the QC and the surrounding cells. Furthermore, the PINFORMED1 (HvPIN1) auxin efflux carrier was found to be expressed in root and shoot meristems, where it polarly localized to the plasma membrane. HvPIN1 expression is negatively regulated by cytokinin and its intracellular localisation is sensitive to brefeldinA (BFA). With this study, we provide the first fluorescent reporter lines as a tool to study auxin and cytokinin signalling and response pathways in barley.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytokinins / pharmacology*
  • Gene Expression Regulation, Developmental / drug effects
  • Gene Expression Regulation, Plant / drug effects
  • Gene Regulatory Networks / drug effects
  • Genes, Reporter
  • Hordeum / drug effects
  • Hordeum / genetics
  • Hordeum / growth & development*
  • In Situ Hybridization, Fluorescence / methods*
  • Indoleacetic Acids / pharmacology*
  • Meristem / drug effects
  • Meristem / genetics
  • Meristem / growth & development
  • Phylogeny
  • Plant Growth Regulators / pharmacology*
  • Plant Proteins / genetics*
  • Plant Roots / drug effects
  • Plant Roots / genetics
  • Plant Roots / growth & development
  • Signal Transduction / drug effects

Substances

  • Cytokinins
  • Indoleacetic Acids
  • Plant Growth Regulators
  • Plant Proteins

Grant support

Work in Rüdiger Simon's lab has been supported by the Deutsche Forschungsgemeinschaft through CEPLAS (EXC1028) (www.ceplas.eu).