Arabidopsis KCBP interacts with AIR9 but stays in the cortical division zone throughout mitosis via its MyTH4-FERM domain

The preprophase band of microtubules performs the crucial function of marking the plane of cell division. Although the preprophase band depolymerises at the onset of mitosis, the division plane is 'memorized' by a cortical division zone to which the phragmoplast is attracted during cytokinesis. Proteins have been discovered that are part of the molecular memory but little is known about how they contribute to phragmoplast guidance. Previously, we found that the microtubule-associated protein AIR9 is found in the cortical division zone at preprophase and returns during cell plate insertion but is absent from the cortex during the intervening mitosis. To identify new components of the preprophase memory, we searched for proteins that interact with AIR9. We detected the kinesin-like calmodulin-binding protein, KCBP, which can be visualized at the predicted cortical site throughout division. A truncation study of KCBP indicates that its MyTH4-FERM domain is required for linking the motor domain to the cortex. These results suggest a mechanism by which minus-end-directed KCBP helps guide the centrifugally expanding phragmoplast to the cortical division site.