Arabidopsis actin-depolymerizing factors (ADFs) 1 and 9 display antagonist activities

► ADF9 does not enhance the rate of actin depolymerization in vitro. ► ADF9 stabilizes and bundles actin filaments in vitro. ► Ectopic expression of ADF9 induces the formation of thick cytoplasmic bundles. ► Data suggest that ADF9 is an atypical member of the ADF family.