Chlorophyll biosynthesis requires a metabolic dialog between the chloroplast envelope and thylakoids where biosynthetic activities are localized. Here, we report the ®rst plant S-adenosyl-L-methionine:Mg-protoporphyrin IX methyltransferase (MgPIXMT) sequence identi®ed in the Arabidopsisgenome owing to its similarity with the Synechocystis sp.