The AP-3 β Adaptin Mediates the Biogenesis and Function of Lytic Vacuoles inArabidopsis   

Abstract

Plant vacuoles are essential multifunctional organelles largely distinct from similar organelles in other eukaryotes. Embryo protein storage vacuoles and the lytic vacuoles that perform a general degradation function are the best characterized, but little is known about the biogenesis and transition between these vacuolar types. Here, we designed a fluorescent markerbased forward genetic screen in Arabidopsis thaliana and identified a protein affected trafficking2 (pat2) mutant, whose lytic vacuoles display altered morphology and accumulation of proteins. Unlike other mutants affecting the vacuole, pat2 is specifically defective in the biogenesis, identity, and function of lytic vacuoles but shows normal sorting of proteins to storage vacuoles. PAT2 encodes a putative b-subunit of adaptor protein complex 3 (AP-3) that can partially complement the corresponding yeast mutant. Manipulations of the putative AP-3 b adaptin functions suggest a plant-specific role for the evolutionarily conserved AP-3 b in mediating lytic vacuole performance and transition of storage into the lytic vacuoles independently of the main prevacuolar compartment-based trafficking route.

The AP-3 adaptor complex is required for vacuolar function in Arabidopsis

“…In the pat4 mutant background, we observed swelling and vacuolization of PVC compartments visualized by PVC markers, such as GFP-RABF2b [34] ( Figure 2E and 2F). Moreover, the swollen PVC phenotype in the pat4 mutant resembled the effect of wortmannin on the PVC morphology [10]. Taken together, these results indicate that aberrant vacuole-like compartments in pat4 mutants can share features of both PVCs and vacuoles.…”

“…By using an ethyl methanesulfonate (EMS)-mutagenized PIN1 pro :PIN1-GFP population we originally identified three independent pat mutant loci from about 1 500 M1 families; among them pat2-1 is defective in the putative β adaptin of the AP-3 complex [10]. In a further genetic screen using the progeny of other 1 920 M1 families we identified two additional non-allelic mutants pat4 and pat5.…”

“…The AP-3-mediated trafficking to the vacuole (in yeast) or lysosomes and lysososome-related organelles (flies and mammals) is supposed to bypass the classical vacuolar trafficking route, which most vacuolar cargos use and that involves late endosomes/prevacuolar compartments multivesicular bodies/(LE/PVC/MVB'S) [5,6,8,9]. Recently, we have shown that the putative AP-3 β protein plays a role in vacuolar function in Arabidopsis, including mediation of the transition between storage and lytic vacuolar identity [10]. In addition, several putative AP-3 adaptins have been identified as suppressors of zigzag 1 (zig1) [11], a mutant affecting a vesicle trafficking regulator, the SNARE VTI11 [12,13].…”

Identification and Dynamics of Arabidopsis Adaptor Protein-2 Complex and Its Involvement in Floral Organ Development

“…Arabidopsis AP-2 has the potential to interact with a vacuolar sorting receptor (Happel et al, 2004). AP-3 plays roles in post-Golgi trafficking and is involved in the regulation of vacuolar biogenesis (Niihama et al, 2009;Feraru et al, 2010;Zwiewka et al, 2011). AP-1 is required for trafficking of the cytokinesis-specific soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) KNOLLE to the cell plate, which mediates proper cell division (Park et al, 2013;Teh et al, 2013).…”

Sorting signals for PIN1 trafficking and localization

“…19 Since the localization of PIN1-GFP in a m2-adaptin mutant was very similar to that in wild-type background, we hypothesized that the lower binding of m2-adaptin cannot be the reason for the accumulation of the PIN1:GFP-F165A mutant in intracellular structures. In contrast, PIN1-GFP accumulated in big intracellular structures in a m3-adaptin mutant, 19 similar to those found in mutants of other subunits of the AP-3 complex, [21][22] suggesting that the AP-3 complex is essential for PIN1 trafficking and localization. However, the precise function of AP-3 in PIN1 trafficking still needs to be elucidated.…”