Plasma membrane‐localized plant immune receptor targets H⁺‐ATPase for membrane depolarization to regulate cell death

Abstract

The hypersensitive response (HR) is a robust immune response mediated by nucleotidebinding, leucine-rich repeat receptors (NLRs). However, the early molecular event that links activated NLRs to cell death is unclear.Here, we demonstrate that NLRs target plasma membrane H + -ATPases (PMAs) that generate electrochemical potential, an essential component of living cells, across the plasma membrane. CC A 309, an autoactive N-terminal domain of a coiled-coil NLR (CNL) in pepper, is associated with PMAs. Silencing or overexpression of PMAs reversibly affects cell death induced by CC A 309 in Nicotiana benthamiana.CC A 309-induced extracellular alkalization causes plasma membrane depolarization, followed by cell death. Coimmunoprecipitation analyses suggest that CC A 309 inhibits PMA activation by preoccupying the dephosphorylated penultimate threonine residue of PMA. Moreover, pharmacological experiments using fusicoccin, an irreversible PMA activator, showed that inhibition of PMAs contributes to CNL-type (but not Toll interleukin-1 receptor NLR-type) resistance protein-induced cell death.We suggest PMAs as primary targets of plasma membrane-associated CNLs leading to HRassociated cell death by disturbing the electrochemical gradient across the membrane. These results provide new insight into NLR-mediated cell death in plants, as well as innate immunity in higher eukaryotes.

The Phytophthora capsici RxLR effector CRISIS2 has roles in suppression of PTI and triggering cell death in host plant

“…Previously, we reported a functional redundancy of several NbPMAs in N. benthamiana (Lee et al, 2022). Co-IP revealed that CRISIS2 also associated with NbPMA1 and NbPMA4, implying that CRISIS2 functions with multiple NbPMAs (Figure 3F).…”

“…PMAs are targeted by multiple pathogens during pathogenesis (Elmore and Coaker, 2011b). Previously, we reported that PM-associated plant CNLs utilized PMAs, including NbPMA3, by inhibiting their activity to promote cell death (Lee et al, 2022). However, whether pathogen effectors could promote cell death through modulation of PMA and the associated molecular mechanisms are still largely unknown.…”

“…Previously, we proposed PMA as the primary target of PM-associated CNLs to facilitate defense-associated cell death (Lee et al, 2022). Here, we hypothesized that pathogen effectors can also utilize the same machinery to promote pathogen virulence.…”

“…To understand the mechanisms underlying PM-associated and effector-mediated plant innate immunity, we developed a series of multiomics and bioinformatics tools for screening the P. capsici RxLR effectors affecting the activity of PMAs and the associated cell death. We employed fusicoccin, an irreversible PMA activator, which inhibits the cell death triggered by PM-associated CNL (Lee et al, 2022). Here, we report that a novel P. capsici RxLR effector, CRISIS2, induces NLR-independent cell death by inhibiting PMA activity.…”

“…Thus, disturbance of the electrochemical gradient across the PM appears to be a general feature of pathogen infection, but the molecular mechanism governing apoplastic acidification or alkalization is still unclear. Recently, several PM-associated coiled-coil (CC) domains of NLRs (CNLs) have been reported to inhibit host PMA activity, resulting in apoplastic alkalization leading to cell death (Lee et al, 2022). Although the apoplastic pH balance regulated by PMA activity plays an important role in diverse plant-pathogen interactions, how PMA activity is affected by various effectors remains to be elucidated.…”