In vascular plants,almost all above-ground organs are de-rived from the shoot apical meristem(SAM).The develop-mental role of the SAM has been extensively studied,especially in the model dicot plant Arabidopsis thaliana(Aichinger et al.,2012).The SAM is spatially divided into three regions:the central zone comprising the stem cells and the organizing center(OC);the peripheral zone that can in-itiate lateral appendages such as leaves and flowers;and the rib zone that is located beneath the central zone and the peripheral zone.In the central zone,the OC provides signals to the stem cells and maintains their activity.In turn,the stem cells provide signals to restrict the number of cells in the OC.In addition,the SAM contains rib meristem activity,which is responsible for internode formation.Strikingly,the SAM is also a virus-free region.It is known that the accumulation of virus particles decreases toward the SAM,and this has led to the development of technologies to culture virus-free plants by SAM tissue culture(Morel and Martin,1952).However,it is unclear why and how the SAM remains free of viruses.Recently,research groups led by Zhao and Tian have made great progress in determining the molecular mechanism of the virus-free nature of the SAM by characterizing the WUSCHEL(WUS)transcription factor(Wu et al.,2020).