Dual-Targeting of Arabidopsis 6-Phosphogluconolactonase 3 （PGL3）to Chloroplasts and Peroxisomes Involves Interaction with Trx m2 in the Cytosol

The oxidative pentose-phosphate pathway （OPPP） represents a central branch of cellular metabolism emanating from glucose-6-phosphate （G6P） to provide reductive power （NADPH） and sugar phosphates for anabolic biosyntheses. In plant cells, the oxidative OPPP branch is found in the cytosol and in plastids, consisting of glucose-6-phosphate dehydrogenase （G6PD）, 6-phosphogluconolactonase （PGL）, and 6-phosphogluconate dehydrogenase （6PGD）. These enzymes are encoded by small gene families in the nuclear genome, which, in Arabidopsis, comprise six G6PD, five 6-PGL, and three 6-PGD isoforms （Kruger and von Schaewen, 2003）. Specific targeting motifs at the C-terminus of 6-PGL and 6-PGD isoforms suggested that the OPPP may also occur in peroxisomes （Reumann et al., 2004）.     

Retromer Subunits VPS35A and VPS29 Mediate Prevacuolar Compartment （PVC） Function in Arabidopsis

Intracellular protein routing is mediated by vesicular transport which is tightly regulated in eukaryotes. The protein and lipid homeostasis depends on coordinated delivery of de novo synthesized or recycled cargoes to the plasma membrane by exocytosis and their subsequent removal by rerouting them for recycling or degradation. Here, we report the characterization of protein affected trafficking 3 （pat3） mutant that we identified by an epifluorescence-based for- ward genetic screen for mutants defective in subcellular distribution of Arabidopsis auxin transporter PIN1-GFR While pat3 displays largely normal plant morphology and development in nutrient-rich conditions, it shows strong ectopic intracellular accumulations of different plasma membrane cargoes in structures that resemble prevacuolar compart- ments （PVC） with an aberrant morphology. Genetic mapping revealed that pat3 is defective in vacuolar protein sorting 35A （VPS35A）, a putative subunit of the retromer complex that mediates retrograde trafficking between the PVC and trans-Golgi network. Similarly, a mutant defective in another retromer subunit, vps29, shows comparable subcellular defects in PVC morphology and protein accumulation. Thus, our data provide evidence that the retromer components VPS35A and VPS29 are essential for normal PVC morphology and normal trafficking of plasma membrane proteins in plants. In addition, we show that, out of the three VPS35 retromer subunits present in Arabidopsis thaliana genome, the VPS35 homolog A plays a prevailing role in trafficking to the lyric vacuole, presenting another level of complexity in the retromer-dependent vacuolar sorting.