Abstract
Plant cells have evolved cortical microtubules in a two-dimensional space beneath the plasma membrane that regulate patterning of cellulose deposition. However, it is still unknown how diverse patterns of cortical microtubules are organized in different xylem cells. Using our newly established in vitro xylem cell differentiation system, we found that a novel microtubule end-tracking protein, MIDD1 (Microtubule Depletion Domain 1), was anchored to distinct plasma membrane domains and promoted local microtubule disassembly, resulting in pits on xylem cell walls. The introduction of RNAi for MIDD1 resulted in failure of local microtubule depletion and the formation of secondary walls without pits. Conversely, the overexpression of MIDD1 reduced microtubule density. MIDD1 has two coiled-coil domains for the binding to microtubules and for the anchorage to plasma membrane domains, respectively. Our results indicate that MIDD1 integrates spatial information in the plasma membrane with cortical microtubule dynamics, for determining xylem cell wall pattern.
