Life after death: are autophagy genes involved in cell death and survival during plant innate immune responses?

Abstract

It has not escaped the attention of the plant disease resistance community that the vacuole is rapidly emerging as a central player in the execution of cell death. On the one hand the targeted destruction of the vacuole-from the inside out-by vacuolar processing enzymes (VPE) is required to induce PCD in pathogen-infected cells. On the other hand, an intact vacuole is vital for a functional autophagic response to ensure survival of uninfected cells. At face value, the two responses seem to represent distinct resistance mechanisms that operate at divergent branch points and their use of the vacuole merely coincidental. However, closer examination has led us to propose an interesting hypothesis that accounts for these two opposing roles of the vacuole in both VPE-mediated PCD and autophagydependent cell survival. During initial infection, we propose a mechanism similar to the CPY transport pathway in yeast wherein a select set of genes, including several which encode a phosphatidylinositol 3-kinase complex that is needed for autophagy, are needed for VPE transport, vacuolar processing and initiation of PCD. Later during infection, autophagyspecific genes are needed for autophagosome formation, sequestration of VPE preproteins and VPE degradation.