Phospholipase Dδ negatively regulates plant thermotolerance by destabilizing cortical microtubules in Arabidopsis

The pattern of cortical microtubule arrays plays an important role in plant growth and adaptation in response to hormonal and environmental changes. Cortical microtubules are connected with the plasma membrane (PM); however, how the membrane affects cortical microtubule organization is not well understood. Here, we showed that phospholipase D delta (PLD) was associated with the PM and co-localized with microtubules in cells. In vitro analysis revealed that PLD bound to microtubules, resulting in microtubule disorganization. Site-specific mutations that decreased PLD delta enzymatic activity impaired its effects on destabilizing microtubule organization. Heat shock transiently activated PLD delta, without any change of its PM localization, triggering microtubule dissociation from PM and depolymerization and seedling death in Arabidopsis, but these effects were alleviated in pld delta knockout mutants. Complementation of pld delta with wild-type PLD delta, but not mutated PLD delta, restored the phenotypes of microtubules and seedling survival to those of wild-type Arabidopsis. Thus, we conclude that the PM-associated PLD delta negatively regulates plant thermotolerance via destabilizing cortical microtubules, in an activity-dependent manner, rather than its subcellular translocation.