Somatic Cytokinesis and Pollen Maturation inArabidopsisDepend on TPLATE, Which Has Domains Similar to Coat Proteins

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Abstract
TPLATE was previously identified as a potential cytokinesis protein targeted to the cell plate. Disruption of TPLATE in Arabidopsis thaliana leads to the production of shriveled pollen unable to germinate. Vesicular compartmentalization of the mature pollen is dramatically altered, and large callose deposits accumulate near the intine cell wall layer. Green fluorescent protein (GFP)-tagged TPLATE expression under the control of the pollen promoter Lat52 complements the phenotype. Downregulation of TPLATE in Arabidopsis seedlings and tobacco (Nicotiana tabacum) BY-2 suspension cells results in crooked cell walls and cell plates that fail to insert into the mother wall. Besides accumulating at the cell plate, GFP-fused TPLATE is temporally targeted to a narrow zone at the cell cortex where the cell plate connects to the mother wall. TPLATE-GFP also localizes to subcellular structures that accumulate at the pollen tube exit site in germinating pollen. Ectopic callose depositions observed in mutant pollen also occur in RNA interference plants, suggesting that TPLATE is implicated in cell wall modification. TPLATE contains domains similar to adaptin and beta-COP coat proteins. These data suggest that TPLATE functions in vesicle-trafficking events required for site-specific cell wall modifications during pollen germination and for anchoring of the cell plate to the mother wall at the correct cortical position.