Opposite changes in membrane fluidity mimic cold and heat stress activation of distinct plant MAP kinase pathways

TLDR

Mitogen‑activated protein kinases (MAPKs) are widely involved in eukaryotic signal transduction, yet no heat‑shock‑activated MAPK has been reported in plants, and the mechanisms of cold‑induced activation of plant MAPKs such as SAMK remain unknown. The study investigates the molecular mechanisms underlying heat‑activation of HAMK and cold‑activation of SAMK. The authors examined membrane fluidity changes, cytoskeletal destabilization, calcium influx, and CDPK involvement to elucidate these activation pathways. They identified a heat‑shock‑activated MAPK (HAMK) and demonstrated that cold activation of SAMK requires membrane rigidification while heat activation requires fluidization; both pathways are mimicked by cytoskeletal destabilizers, blocked by the actin stabilizer jasplakinolide, and inhibited by calcium influx blockade or CDPK antagonism, indicating that temperature is sensed through membrane structural changes that signal via the cytoskeleton, Ca²⁺ fluxes, and CDPKs to distinct MAPK cascades.

Abstract

Summary Mitogen‐activated protein kinases (MAPKs) appear to be ubiquitously involved in signal transduction during eukaryotic responses to extracellular stimuli. In plants, no heat shock‐activated MAPK has so far been reported. Also, whereas cold activates specific plant MAPKs such as alfalfa SAMK, mechanisms of such activation are unknown. Here, we report a heat shock‐activated MAPK (HAMK) immunologically related to ERK (Extracellular signal‐Regulated Kinase) superfamily of protein kinases. Molecular mechanisms of heat‐activation of HAMK and cold‐activation of SAMK were investigated. We show that cold‐activation of SAMK requires membrane rigidification, whereas heat‐activation of HAMK occurs through membrane fluidization. The temperature stress‐ and membrane structure‐dependent activation of both SAMK and HAMK is mimicked at 25°C by destabilizers of microfilaments and microtubules, latrunculin B and oryzalin, respectively; but is blocked by jasplakinolide, a stabilizer of actin microfilaments. Activation of SAMK or HAMK by temperature, chemically modulated membrane fluidity, or by cytoskeleton destabilizers is inhibited by blocking the influx of extracellular calcium. Activation of SAMK or HAMK is also prevented by an antagonist of calcium‐dependent protein kinases (CDPKs). In summary, our data indicate that cold and heat are sensed by structural changes in the plasma membrane that translates the signal via cytoskeleton, Ca 2+ fluxes and CDPKs into the activation of distinct MAPK cascades.