MAP Kinase 6-mediated activation of vacuolar processing enzyme modulates heat shock-induced programmed cell death in Arabidopsis.

• Vacuolar processing enzyme (VPE), a cysteine protease, has been intensively studied in plant hypersensitive cell death, but the role and molecular mechanism of VPEs in response to abiotic stresses remain unclear. This work investigated the involvement of VPEs in Arabidopsis response to heat stress. • Under heat shock (HS), Arabidopsis VPE activity and the transcript level of γVPE were both upregulated, and γVPE deficiency suppressed vacuolar disruption and delayed caspase-3-like activation in HS-induced programmed cell death (PCD). Moreover, the change of VPE activity generally paralleled the alteration of caspase-1-like activity under HS treatment, indicating that HS-induced VPE activity might exhibit the caspase-1-like activity. • Further studies showed that MAP Kinase 6 (MPK6) activity was increased after HS treatment, and experiments with inhibitors and mutants suggested that MPK6 was responsible for the γVPE activation after HS treatment. In response to HS stress, reactive oxygen species (ROS) production, increase of cytoplasmic calcium concentration (Ca(2+) ) and the upregulation of calmodulin 3 (CaM3) transcript level occurred upstream of MPK6 activation. • Our results suggested that activation of Arabidopsis γVPE was mediated by MPK6 and played an important role in HS-induced Arabidopsis PCD, providing new insight into the mechanistic study of plant VPEs.