ANXUR receptor-like kinases coordinate cell wall integrity with growth at the pollen tube tip via NADPH oxidases

PLoS Biol. 2013 Nov;11(11):e1001719. doi: 10.1371/journal.pbio.1001719. Epub 2013 Nov 26.

Abstract

It has become increasingly apparent that the extracellular matrix (ECM), which in plants corresponds to the cell wall, can influence intracellular activities in ways that go far beyond their supposedly passive mechanical support. In plants, growing cells use mechanisms sensing cell wall integrity to coordinate cell wall performance with the internal growth machinery to avoid growth cessation or loss of integrity. How this coordination precisely works is unknown. Previously, we reported that in the tip-growing pollen tube the ANXUR receptor-like kinases (RLKs) of the CrRLK1L subfamily are essential to sustain growth without loss of cell wall integrity in Arabidopsis. Here, we show that over-expression of the ANXUR RLKs inhibits growth by over-activating exocytosis and the over-accumulation of secreted cell wall material. Moreover, the characterization of mutations in two partially redundant pollen-expressed NADPH oxidases coupled with genetic interaction studies demonstrate that the ANXUR RLKs function upstream of these NADPH oxidases. Using the H₂O₂-sensitive HyPer and the Ca²⁺-sensitive YC3.60 sensors in NADPH oxidase-deficient mutants, we reveal that NADPH oxidases generate tip-localized, pulsating H₂O₂ production that functions, possibly through Ca²⁺ channel activation, to maintain a steady tip-focused Ca²⁺ gradient during growth. Our findings support a model where ECM-sensing receptors regulate reactive oxygen species production, Ca²⁺ homeostasis, and exocytosis to coordinate ECM-performance with the internal growth machinery.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / cytology
  • Arabidopsis / enzymology*
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / physiology*
  • Calcium / metabolism
  • Cell Wall / enzymology
  • Exocytosis
  • Extracellular Matrix / metabolism
  • Germination
  • Homeostasis
  • Hydrogen Peroxide / metabolism
  • NADPH Oxidases / genetics*
  • NADPH Oxidases / metabolism
  • Plant Infertility
  • Pollen Tube / cytology
  • Pollen Tube / enzymology*
  • Pollen Tube / growth & development
  • Protein Kinases / physiology*

Substances

  • Arabidopsis Proteins
  • Hydrogen Peroxide
  • NADPH Oxidases
  • ANXUR1 protein, Arabidopsis
  • ANXUR2 protein, Arabidopsis
  • Protein Kinases
  • Calcium

Grant support

This work was supported by the University of Zürich, the Forschungskredit der Universität Zürich and the European Union through a Marie Curie International Reintegration grant to ABD, and grants of the Swiss National Science Foundation (31003AB-126006 and 31003A_141245) and SystemsX.ch (iPhD and an RTD project “Plant Growth”) to UG. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.