Rice kinesin-related protein STD1 and microtubule-associated protein MAP65-5 cooperatively control microtubule bundling.

STD1 specifically interacts with MAP65-5 in rice and they cooperatively control microtubule bundles in phragmoplast expansion during cell division. Microtubules play critical roles during the cell cycle progression in the plant cell. We previously reported that STEMLESS DWARF 1 (STD1), a kinesin-related protein, was localized specifically to the phragmoplast midzone during telophase to regulate the lateral expansion of phragmoplast in rice (Oryza sativa). However, how STD1 regulates microtubule organization remains unknown. Here, we found that STD1 interacted directly with MAP65-5, a member of the microtubule-associated proteins (MAPs). Both STD1 and MAP65-5 could form homodimers and bundle microtubules individually. Compared with MAP65-5, the microtubules bundled by STD1 were disassembled completely into single microtubules after adding ATP. Conversely, the interaction of STD1 with MAP65-5 enhanced the microtubule bundling. These results suggest STD1 and MAP65-5 might cooperatively regulate microtubule organization in the phragmoplast at telophase.