Cytokinesis in Arabidopsis: Cytokinetic vesicles, cargo proteins and fusion machinery

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In plant cytokinesis, the partitioning membrane originates through target delivery of secretory vesicles to the cell division plane and the fusion of vesicles with one another, generating the cell plate. It is not known what proteins are transported and what role they play in cytokinesis. The cytokinetic vesicles bear so-called cis-complexes of SNARE proteins, which are enzymatically disassembled; subsequently, so-called SM proteins mediate the formation of trans-complexes of complementary SNARE proteins that facilitate the fusion between adjacent vesicles. Regulatory mechanisms underlying the reorganisation of cis to trans-SNARE complexes in cytokinesis are not known.(1) A major objective of the proposed research is to identify cargo proteins that are delivered on KNOLLE-bearing membrane vesicles to the plane of cell division and contribute to the formation or maturation of the partitioning membrane and/or the synthesis or assembly of the forming cross wall. Depending on the number of proteins to be identified, we will primarily focus our functional analysis on proteins that appear specifically involved in cytokinesis.(2) Another objective is to identify the AAA+ ATPase and its alpha-SNAP adaptor involved in cis-SNARE complex disassembly prior to cell plate formation and to characterise their action in cytokinesis. We will also address whether the capture of monomeric Qa-SNARE KNOLLE by SM protein KEULE involves direct physical interaction with the disassembling machinery.(3) A third objective is to analyse the interaction between Qa-SNAREs and SM proteins in cytokinesis by identifying specificity determinants that distinguish SM protein KEULE from its paralogue SEC1B in interaction with KNOLLE and by defining relevant KNOLLE sequence motifs required for SM interaction. We will also determine whether KEULE and SEC1B interact with SYP132 in the same or a different manner compared to KNOLLE.