In canonical microtubule-based transport, adaptor proteins link cargos to dynein and kinesin motors. Recently, an alternative mode of transport known as ‘hitchhiking’ was discovered, where cargos achieve motility by hitching a ride on already-motile cargos, rather than attaching to a motor protein. Hitchhiking has been best-studied in two filamentous fungi, Aspergillus nidulans and Ustilago maydis. In U. maydis, ribonucleoprotein complexes, peroxisomes, lipid droplets, and endoplasmic reticulum hitchhike on early endosomes. In A. nidulans, peroxisomes hitchhike using a putative molecular linker, PxdA, which associates with early endosomes. However, whether other organelles use PxdA to hitchhike on early endosomes is unclear, as are the molecular mechanisms that regulate hitchhiking. Here we find that the proper distribution of lipid droplets, mitochondria and pre-autophagosomes do not require PxdA, suggesting that PxdA is a peroxisome-specific molecular linker. We identify two new pxdA alleles, including a point mutation (R2044P) that disrupts PxdA's ability to associate with early endosomes and reduces peroxisome movement. We also identify a novel regulator of peroxisome hitchhiking, the phosphatase DipA. DipA co-localizes with early endosomes and its early endosome-association relies on PxdA. Together, our data suggest that PxdA and the DipA phosphatase are specific regulators of peroxisome hitchhiking on early endosomes.

在典型的基于微管的运输中，衔接蛋白将货物与动力蛋白和驱动蛋白马达连接起来。最近，人们发现了另一种被称为“搭便车”的运输方式，其中货物通过搭便车来实现运动，而不是附着在运动蛋白上。搭便车在两种丝状真菌——构巢曲霉和黑粉虱中得到了最好的研究。在玉米葡萄球菌中，核糖核蛋白复合物、过氧化物酶体、脂滴和内质网在早期内体上搭便车。在构巢曲霉, 过氧化物酶体使用与早期内体相关的假定分子接头 PxdA 搭便车。然而，其他细胞器是否使用 PxdA 在早期内体上搭便车以及调节搭便车的分子机制尚不清楚。在这里，我们发现脂滴、线粒体和前自噬体的正确分布不需要 PxdA，这表明 PxdA 是一种过氧化物酶体特异性分子接头。我们确定了两个新的pxdA等位基因，包括一个点突变 (R2044P)，它破坏了 PxdA 与早期内体结合并减少过氧化物酶体运动的能力。我们还确定了一种新的过氧化物酶体搭便车调节剂，即磷酸酶 DipA。DipA 与早期内体共定位，其早期内体结合依赖于 PxdA。总之，我们的数据表明 PxdA 和 DipA 磷酸酶是过氧化物酶体在早期内体上搭便车的特异性调节剂。