Acto-Myosin motorises the flow of auxin

Auxin has always been a hormone of intensive investigation because of its crucial roles in plant growth. With the recent confirmation of PIN1 and AUX1 as proteins specifically controlling auxin distribution, the ongoing debate about possible mechanisms in polar auxin transport (PAT) made further progress. Another new set of data suggested vesicle-based processes to have meaningful roles in auxin pathways. This view got additional support by the finding that cytoplasmic streaming as well as PAT decreased under inhibition of actin or myosin. Inhibitory effects on both events were also observed when actin-binding proteins (ABPs) were overexpressed for fluorescent actin-labelling. Here, the block of motility was reasoned by myosins and ABPs competing for F-actin binding. In summary, the observations constantly show that acto-myosin controls the motility of vesicles and in parallel, is essential for directional auxin flow. A direct functional link between PAT and vesicles can not be concluded from these experiments, but might be either understood as the shuttling of components of the auxin-efflux machinery by myosin-guided vesicles, or, in the more unusual meaning of PAT by secretion, as the delivery of auxin in membraneous compartments moved by myosin.