The plant specific VPS2.2/HYADE of the ESCRT-III protein sorting machinery localizes to a secretory compartment and is required for cell division plane determination in Arabidopsis

Positioning of the division plane is a critical step during cellular development. While in animal cells the plane of cell division is defined during metaphase, in plants this decision is made before mitosis and includes the formation of a cytoskeletal structure termed the preprophase band (PPB). Although not essential, the PPB constitutes the earliest mark for the plane of cell division and coincides with the sites where the cell plate fuses with the parental plasma membrane during cytokinesis. Recent studies indicate that endo- and exocytosis are involved in remodelling of the cortical division zone. Here we show that PPBs, phragmoplasts, cell plates and cell walls are misplaced in Arabidopsis mutants of Atvps2.2/hyade (hya), a plant-specific component of the Endosomal Sorting Complex Required for Transport (ESCRT)-III. We demonstrate that the amino acid substitution Q71P of the hya-3 allele abolishes the homo- and heteromerization with other ESCRT-III components. Functional HYA-GFP fusion proteins are excluded from the canonical location of ESCRT-III complexes at multivesicular bodies (MVBs) and are absent from Brefeldin A (BFA) and Wortmannin (WM) sensitive compartments in Arabidopsis. HYA-GFP neither localize to early nor late endosomes but colocalizes with markers of secretory compartments such as the Qc-SNARE, SYP61 and with trans-Golgi-network (TGN) derived secretory Rab-A3 vesicles. Moreover, HYA-GFP locates to the extracellular space indicating that VPS2.2/HYA is involved in secretion. These results are consistent with a novel, non-canonical function of ESCRT-III in the establishment and maintenance of the cortical division zone via secretion.