The regulation of programmed cell death (PCD) and autophagy are crucial for the fitness of plants when encountering extrinsic stress. Over two decades, research on plant metacaspases has mainly concentrated on the role of these cysteine proteases in PCD. Emerging data now indicate that metacaspases might also interfere with the autophagy regulatory network. In this thesis, I present the analysis of metacapase-5 (AtMC5) functions in regulating endoplasmic reticulum (ER) stress-induced PCD and autophagy in Arabidopsis thaliana. AtMC5 exhibited a positive regulation of PCD as both ion leakage and caspase-3-like activities are reduced in the atmc5 knockout seedlings. In response to ER stress, AtMC5 is required for the cleavage of Defender against Apoptotic Death-1 (AtDAD1) and potential cleavage site(s) have been identified. Furthermore, an AtDAD1 fusion with Green Fluorescent Protein (GFP) was loaded into autophagic bodies during prolonged ER stress. A selective autophagy of the ER, ER-phagy, was evident in ER-stressed root cells and TEM studies identified multiple-membrane vesicles containing ER whorls corresponding to ER-phagosomes. Interestingly, atmc5 loss of function caused an increase in autophagic bodies/ ER-phagosome counts per cell, suggesting that AtMC5 might apply a break on auto/ ER-phagy. Taken together, these data place firmly AtMC5 and the cleavage of AtDAD1 at the intersection of PCD and auto/ ER-phagy, opening new avenues to the study of the key interaction between these two cellular processes.