MOR1/GEM1 plays an essential role in the plant-specific cytokinetic phragmoplast

MOR1 is a member of the MAP215 family of microtubule-associated proteins and is required to establish interphase cortical microtubule arrays in plant cells. Here we show that MOR1 binds microtubules in vivo, localising to both cortical microtubules and to areas of overlapping microtubules in the phragmoplast. We demonstrate an essential role for MOR1 in cytokinesis through genetic complementation of the cytokinesis defective gem1-1 mutation with MOR1. Phenotypic analysis of gem1-1 and a T-DNA insertion allele gem1-2 confirm that MOR1/GEM1 is essential for regular patterns of cytokinesis. Both mutations, gem1-1 and gem1-2, cause the truncation of MOR1/GEM1. Moreover, the C-terminal domain absent in both mutants binds microtubules in vitro. These data demonstrate that MOR1/GEM1 plays an essential role in the cytokinetic phragmoplast.