Clustering of a kinesin-14 motor enables processive retrograde microtubule-based transport in plants

Abstract

The molecular motors kinesin and dynein drive bidirectional motility along microtubules (MTs) in most eukaryotic cells1,2. Land plants, however, are a notable exception, since they contain a large number of kinesins but lack cytoplasmic dynein, the foremost processive retrograde transporter3,4. It remains unclear how plants achieve retrograde cargo transport without dynein. Here, we have analyzed the motility of the six members of minus-end-directed kinesin-14 motors in the moss Physcomitrella patens and found that none are processive as native dimers. However, when artificially clustered into as little as dimer of dimers, the type-VI kinesin-14 (a homologue of Arabidopsis KCBP [kinesin-like calmodulin binding protein]) exhibited highly processive and fast motility (up to 0.6 μm/s). Multiple kin14-VI dimers attached to liposomes also induced transport of this membrane cargo over several microns. Consistent with these results, in vivo observations of GFP-tagged kin14-VI in moss cells revealed fluorescent punctae that moved processively towards the minus ends of the cytoplasmic MTs. These data suggest that clustering of a kinesin-14 motor serves as a dynein-independent mechanism for retrograde transport in plants.