Root hair curling and Rhizobium infection in Medicago truncatula are mediated by phosphatidylinositide-regulated endocytosis and reactive oxygen species

Smadar Peleg-Grossman, Hanne Volpin, Alex Levine*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

115 Scopus citations

Abstract

The symbiotic relationships between legumes and rhizobacteria involve extensive signalling between the two organisms. Studies using genetic, biochemical, and pharmacological approaches have demonstrated the involvement of calcium and reactive oxygen species in the establishment of symbiotic interactions. In the early stage of the interactions rhizobia grow as infection thread within host root hairs and are internalized into the plant cells via endocytosis. It is shown here that inoculation of Medicago truncatula roots with Sinorhizobium meliloti induced a battery of vesicle trafficking genes, including the phosphatidylinositol 3-kinase (PI3K) gene that stimulated plasma membrane endocytosis and the production of reactive oxygen species (ROS). Inhibition of the PI3K suppressed the membrane endocytosis and subsequent oxidative burst and prevented root hair curling and formation of infection threads. Similar effects were produced by inhibition of PtdIns-specific phospholipase C (PI-PLC). However, neither inhibition of PI3K nor PI-PLC signalling blocked cytosolic Ca2+ influx or early nodulin (ENOD) gene expression. By contrast, the inhibitors induced ENODs transcription in the absence of Rhizobium, suggesting that the expression of ENODs responds to plasma membrane perturbations. In summary, the results show a major reprogramming of intracellular vesicle trafficking during the early stages of symbiotic interactions that co-ordinate the host responses. Activation of parallel signalling pathways leading to Cacyt2+ influx and ROS production that regulate the root hair curling and ENODs expression are also shown.

Original languageAmerican English
Pages (from-to)1637-1649
Number of pages13
JournalJournal of Experimental Botany
Volume58
Issue number7
DOIs
StatePublished - Apr 2007

Bibliographical note

Funding Information:
We thank Y Kapulnik (Volcani Center) for M. truncatula seeds and comments on the manuscript and Naomi Book-Melamed for confocal microscopy analysis. This research was supported by the Israel Science Foundation and by an EMBO fellowship ASTF 58-2006 to SP-G.

Keywords

  • Endocytosis
  • Phosphatidylinositol-3 kinase
  • Reactive oxygen species

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