The orchestrated down‐regulation of levels of major enzymes involved in the MTC (MS, SAMS, SAHH) and MTC‐related folate cycle (SHM and MTHFR) in potato leaves systemically infected with PVY observed at the early stage (8 dpi) of infection at 28 °C is perhaps one of the most intriguing findings of this study. This evidence concerns the gene MTHFR and infection.