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

Abstract

The preprophase band of microtubules performs a critical function by marking the plane of plant 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. Microtubule-associated AIR9 recognizes the cortical division zone at preprophase and during cell plate insertion but is absent from the cortex during mitosis itself. With the aim of identifying new components of the preprophase memory we searched for protein interactors of AIR9. One of these, the kinesin-like calmodulin binding protein, KCBP, remains at the predicted cortical site throughout division as shown by live-cell microscopy. A truncation study of KCBP indicates that its MyTH4-FERM domain is required for linking the motor to the cortex. Our results suggest a mechanism in which microtubule minus end-directed KCBP is involved in guiding the centrifugally expanding phragmoplast to the cortical division site