We studied the function of PG localized protease, PGM48 both in vitro and in vivo during natural senescence in Arabidopsis thaliana.Our results show that PGM48 is a metalloprotease and a senescence inducible protein. In vitro assay by recombinant protein revealed a proteolytic activity. Quantitative proteome analysis of PGs from senescing rosettes of overexpression plants lines showed a significantly reduced level of CAROTENOID CLEAVAGE ENZYME 4 ( CCD4) protein but 2-3 fold higher level of phytyl-esterase (PES1) compared to wild type; the opposite results were found in RNAi lines. Yeast-2-hybrid analysis and in vitro pull-down experiments showed that PGM48 interacts with the kinase ABC1K3, PES1 and CCD4, but not with chlorophyll catabolic enzymes. We propose that PGM48 acts as a positive regulator of leaf senescence.