Activation of MAPK-mediated immunity by phosphatidic acid in response to positive-strand RNA viruses

Increasing evidences suggested mitogen-activated protein kinase (MAPK) cascades played a crucial role in plant defense against virus. However, the mechanisms underlying the activation of MAPK cascades in response to viral infection remain unclear. In this study, we discovered phosphatidic acid (PA) represented a major lipid class that responded to Potato virus Y(PVY) at an early stage. We identified NbPLDα1 (Nicotiana benthamianaPhospholipase Dα1) as the key enzyme responsible for PVY-increased PA level, and found that it played an antiviral role. 6K2 of PVY interacts with NbPLDα1, leading to elevated PA level. Additionally, NbPLDα1 and PA are recruited by 6K2 to membrane-bound viral replication complexes. On the other hand, 6K2 induces the activation of MAPK pathway, dependent on its interaction with NbPLDα1 and the derived PA. PA binds to WIPK/SIPK/NTF4, prompting them to phosphorylate WRKY8. Notably, spraying with exogenous PA is sufficient to activate MAPK pathway. Knockdown of MEK2-WIPK/SIPK-WRKY8 cascade results in enhanced accumulation of PVY genomic RNA. Furthermore, 6K2 of Turnip mosaic virus(TuMV) and p33 of Tomato bushy stunt virus(TBSV) also interact with NbPLDα1 and induce the activation of MAPK-mediated immunity. Loss function of NbPLDα1 inhibits virus-induced activation of MAPK cascades and promotes viral RNA accumulation. Thus, activation of MAPK-mediated immunity by NbPLDα1-deived PA is a common strategy employed by hosts to counteract positive-strand RNA virus infection.