The Arabidopsis pex12 and pex13 mutants are defective in both PTS1- and PTS2-dependent protein transport to peroxisomes

Peroxisome biogenesis requires various complex processes including organelle division, enlargement and protein transport. We have been studying a number of Arabidopsis apm mutants that display aberrant peroxisome morphology. Two of these mutants, apm2 and apm4, showed green fluorescent protein fluorescence in the cytosol as well as in peroxisomes, indicating a decrease of efficiency of peroxisome targeting signal 1 (PTS1)-dependent protein transport to peroxisomes. Interestingly, both mutants were defective in PTS2-dependent protein transport. Plant growth was more inhibited in apm4 than apm2 mutants, apparently because protein transport was more severely decreased in apm4 than in apm2 mutants. APM2 and APM4 were found to encode proteins homologous to the peroxins PEX13 and PEX12, respectively, which are thought to be involved in transporting matrix proteins into peroxisomes in yeasts and mammals. We show that APM2/PEX13 and APM4/PEX12 are localized on peroxisomal membranes, and that APM2/PEX13 interacts with PEX7, a cytosolic PTS2 receptor. Additionally, a PTS1 receptor, PEX5, was found to stall on peroxisomal membranes in both mutants, suggesting that PEX12 and PEX13 are components that are involved in protein transport on peroxisomal membranes in higher plants. Proteins homologous to PEX12 and PEX13 have previously been found in Arabidopsis but it is not known whether they are involved in protein transport to peroxisomes. Our findings reveal that APM2/PEX13 and APM4/PEX12 are responsible for matrix protein import to peroxisomes in planta.

过氧化物酶体的生物发生需要多种复杂过程，包括细胞器分裂、增大和蛋白质运输。我们一直在研究一些拟南芥apm突变体，它们表现出过氧化物酶体形态异常。其中两个突变体apm2和apm4在细胞质以及过氧化物酶体中都显示绿色荧光蛋白荧光，这表明过氧化物酶体靶向信号1（PTS1）依赖的蛋白质向过氧化物酶体运输的效率降低。有趣的是，这两个突变体在PTS2依赖的蛋白质运输方面都存在缺陷。apm4突变体中的植物生长比apm2突变体受到更严重的抑制，显然是因为apm4突变体中蛋白质运输比apm2突变体中降低得更严重。发现APM2和APM4分别编码与过氧化物酶体相关蛋白PEX13和PEX12同源的蛋白质，它们被认为参与酵母和哺乳动物中基质蛋白质向过氧化物酶体的运输。我们表明APM2/PEX13和APM4/PEX12定位在过氧化物酶体膜上，并且APM2/PEX13与细胞质中的PTS2受体PEX7相互作用。此外，发现PTS1受体PEX5在两个突变体中都停滞在过氧化物酶体膜上，这表明PEX12和PEX13是高等植物中参与过氧化物酶体膜上蛋白质运输的组分。先前在拟南芥中已经发现了与PEX12和PEX13同源的蛋白质，但不知道它们是否参与蛋白质向过氧化物酶体的运输。我们的研究结果揭示APM2/PEX13和APM4/PEX12负责植物体内基质蛋白质向过氧化物酶体的输入。