The septins are filament-forming, GTP-binding proteins that are conserved from 
yeast to humans. Septins assemble into higher-order structures such as rings, 
bars, and gauzes with diverse functions including serving as membrane diffusion 
barriers and scaffolds for cell signaling. The basis for septin filament 
polymerization and the rules governing septin polymer dynamics are presently not 
well understood. Pharmacological agents are essential tools in studying such 
properties of the actin and microtubule cytoskeletons however there are only 
limited reports of a drug specific to the septin cytoskeleton. Forchlorfenuron 
(FCF) is a synthetic plant cytokinin used in agriculture which has been shown to 
alter septin organization in yeast and mammalian tissue culture cells. Here we 
assess cellular requirements and properties of septin-based structures induced 
by FCF. Treatment of the filamentous fungus Ashbya gossypii with FCF leads to 
assembly of extensive septin fibers throughout hyphae which is rapidly reversed 
upon removal of the drug. These fibers do not exchange or add septin subunits 
after assembly, indicating that FCF suppresses normal septin dynamics and 
stabilizes the polymers. While FCF-induced septin fibers do not co-localize to 
actin or microtubules, a polarized F-actin cytoskeleton is likely required for 
the assembly of drug-induced septin fibers. Thus, FCF is a potent inducer of 
septin polymerization and acts as a reversible stabilizer of extended septin 
polymers. This drug will be a powerful tool for studying mechanisms of septin 
polymerization and function, particularly in cell types where molecular analyses 
are complicated by the presence of multiple isoforms and limited genetics.