MYB1 is an important transcriptional factor that regulates anthocyanin biosynthesis in red-skinned apples (Malus domestica), but little is known about its posttranslational regulation.Here, we show that MdMYB 1 interacts with MdSIZ1 as a SUMO E3 ligase in vitro and in vivo.MdMYB1 was efficiently sumoylated by MdSIZ1 under adverse temperature conditions, and this sumoylation was required for MdMYB 1 protein stability.