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Mai1 Protein Acts Between Host Recognition of Pathogen Effectors and Mitogen-Activated Protein Kinase Signaling

Robyn Roberts1, Sarah R Hind1, Kerry F Pedley1

  • 1Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, U.S.A.

Molecular Plant-Microbe Interactions : MPMI
|June 29, 2019
PubMed

Insights

Researchers identified SlMai1, a protein linking plant immune receptors (NLRs) to defense signaling. SlMai1 connects pathogen detection to mitogen-activated protein kinase (MAPK) cascades, crucial for plant immunity and programmed cell death (PCD).

Area of Science:

  • Plant immunity
  • Molecular plant-pathogen interactions
  • Signal transduction

Background:

  • The connection between plant immune receptors (NLRs) detecting pathogens and downstream defense signaling pathways, specifically mitogen-activated protein kinase (MAPK) cascades, remains unclear.
  • MAPK signaling, activated by MAPKKKα (M3Kα), is known to trigger programmed cell death (PCD) during NLR-mediated immunity.

Purpose of the Study:

  • To elucidate the molecular mechanisms linking NLR-mediated pathogen recognition to MAPK signaling cascades.
  • To identify and characterize novel proteins involved in this immune signaling pathway.

Main Methods:

  • Virus-induced gene silencing (VIGS) in *Nicotiana benthamiana* to study the function of *Mai1* homologs.
  • Co-expression assays to investigate protein-protein interactions and functional complementation.
  • Analysis of programmed cell death (PCD) induction and MAPK phosphorylation levels.

Main Results:

  • A tomato M3Kα-interacting protein, SlMai1, was identified, showing high homology to *Arabidopsis* brassinosteroid kinase 1 (AtBsk1) but exhibiting functional divergence.
  • Silencing of *Mai1* homologs in *N. benthamiana* led to increased susceptibility to *Pseudomonas syringae* and impaired NLR-induced PCD.
  • Expression of a synthetic *SlMai1* gene restored PCD, while AtBsk1 did not, indicating SlMai1's specific role.
  • Mai1 acts upstream of M3Kα/MKK2 in the PCD pathway, and its co-expression with M3Kα enhances MAPK phosphorylation and accelerates PCD.

Conclusions:

  • SlMai1 acts as a crucial molecular link between host pathogen recognition by NLRs and the activation of MAPK signaling cascades.
  • This finding provides new insights into the early steps of plant immune signaling and programmed cell death.
  • SlMai1 represents a potential target for enhancing plant disease resistance.
Keywords:
NLR-triggered immunityPseudomonas syringaebacterial speck diseaseplant immunitysignal transductiontomato

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