Directional cell expansion is a fundamental process that is involved in virtually all cellular processes.Divergence from isotropic growth is commonly associated with cell fate transition,organ shaping,or cell maturation.To obtain continuous direc-tional cell growth,and tissue and organ growth as well,positive feedback loops are needed to lock anisotropic cell expansion.On the other hand,antagonistic mechanisms are needed to terminate directional cell expansion.Many genes affecting cell shape have been identified,but only in a few cases do we under-stand the precise chains of molecular events to some extent.Recently,a cortical microtubule(CMT)-mediated mechanical feedback loop has been recognized that amplifies tensile stress anisotropy and leads to expansion perpendicular to the stress di-rection(Sampathkumar,2020;Zhao et al.,2020)(Figure 1A).By contrast,passive reorientation of cellulose microfibrils(CMFs)may form a combative mechanism that cancels directional cell expansion(Figure 1B).However,passive CMF reorientation is insufficiently recognized by developmental biologists who are interested in directional cell expansion,anisotropic tissue growth,and organ shaping.