METACASPASE9 modulates autophagy to confine cell death tothe target cells during Arabidopsis vascular xylem differentiation

We uncovered that the level of autophagy in plant cells undergoingprogrammed cell death determines the fate of the surrounding cells.Our approach consisted of using Arabidopsis thaliana cell culturescapable of differentiating into two different cell types: vasculartracheary elements (TEs) that undergo programmed cell death(PCD) and protoplast autolysis, and parenchymatic non-TEs thatremain alive. The TE cell type displayed higher levels of autophagywhen expression of the TE-specific METACASPASE9 (MC9) wasreduced using RNAi (MC9-RNAi). Misregulation of autophagy in theMC9-RNAi TEs coincided with ectopic death of the non-TEs, implyingthe existence of an autophagy-dependent intercellular signallingfrom within the TEs towards the non-TEs. Viability of the non-TEswas restored when AUTOPHAGY2 (ATG2) was downregulatedspecifically in MC9-RNAi TEs, demonstrating the importance ofautophagy in the spatial confinement of cell death. Our resultssuggest that other eukaryotic cells undergoing PCD might also needto tightly regulate their level of autophagy to avoid detrimentalconsequences for the surrounding cells.Bio4Energ