Peroxisomes are dynamic and metabolically plastic organelles. Their multiplicity of functions impacts on many aspects of plant development and survival. New functions for plant peroxisomes such as in the synthesis of biotin, ubiquinone and phylloquinone are being uncovered and their role in generating reactive oxygen species (ROS) and reactive nitrogen species (RNS) as signalling hubs in defence and development is becoming appreciated. Understanding of the biogenesis of peroxisomes, mechanisms of import and turnover of their protein complement, and the wholesale destruction of the organelle by specific autophagic processes is giving new insight into the ways that plants can adjust peroxisome function in response to changing needs.

The development of ‘designer’ organelles could be a key strategy to enable foreign pathways to be efficiently controlled within eukaryotic biotechnology. A fundamental component of any such system will be the implementation of a bespoke protein import pathway that can selectively deliver constituent proteins to the new compartment in the presence of existing endogenous trafficking systems. Here we show that the protein–protein interactions that control the peroxisomal protein import pathway can be manipulated to create a pair of interacting partners that still support protein import in moss cells, but are orthogonal to the naturally occurring pathways. In addition to providing a valuable experimental tool to give new insights into peroxisomal protein import, the variant receptor-signal sequence pair forms the basis of a system in which normal peroxisomal function is downregulated and replaced with an alternative pathway, an essential first step in the creation of a designer organelle.

SummaryFatty acid b-oxidation is an essential process in many aspects of plant development, and storage oil in the form of triacylglycerol (TAG) is an important food source for humans and animals, for biofuel and for industrial feedstocks. In this study we characterize the effects of a small molecule, diphenyl methylphosphonate, on oil mobilization in Arabidopsis thaliana.Confocal laser scanning microscopy, transmission electron microscopy and quantitative lipid profiling were used to examine the effects of diphenyl methylphosphonate treatment on seedlings.Diphenyl methylphosphonate causes peroxisome clustering around oil bodies but does not affect morphology of other cellular organelles. We show that this molecule blocks the breakdown of pre-existing oil bodies resulting in retention of TAG and accumulation of acyl CoAs. The biochemical and phenotypic effects are consistent with a block in the early part of the b-oxidation pathway.Diphenyl methylphosphonate appears to be a fairly specific inhibitor of TAG mobilization in plants and whilst further work is required to identify the molecular target of the compound it should prove a useful tool to interrogate and manipulate these pathways in a controlled and reproducible manner.

Auxin gradients are established and maintained by polarized distribution of auxin transporters that undergo constitutive endocytic recycling from the PM (plasma membrane) and are essential for the gravitropic response in plants. The present study characterizes an inhibitor of endomembrane protein trafficking, TE1 (trafficking and endocytosis inhibitor 1/TENin1) that reduces gravitropic root bending in Arabidopsis thaliana seedlings. Short-term TE1 treatment causes accumulation of PM proteins, including the BR (brassinosteroid) receptor BRI1 (BR insensitive 1), PIP2a (PM intrinsic protein 2a) and the auxin transporter PIN2 (PIN-FORMED 2) in a PVC (pre-vacuolar related compartment), which is sensitive to BFA (Brefeldin A). This compound inhibits endocytosis from the PM and promotes trafficking to the vacuole, consistent with inhibition of retrieval of proteins to the TGN (trans-Golgi network) from the PVC and the PM. However, trafficking of newly synthesized proteins to the PM is unaffected. The short-term protein trafficking inhibition and long-term effect on plant growth and survival caused by TE1 were fully reversible upon drug washout. Structure–activity relationship studies revealed that only minor modifications were possible without loss of biological activity. Diversity in Arabidopsis ecotypes was also exploited to identify two Arabidopsis accessions that display reduced sensitivity to TE1. This compound and the resistant Arabidopsis accessions may be used as a resource in future studies to better understand endomembrane trafficking in plants.

Peroxisomes are dynamic eukaryotic organelles that perform a wide range of important metabolic processes. In plants, the peroxisome is the sole organelle to carry out β‐oxidation of fatty acids, break down hydrogen peroxide, and performs several other functions required at different stages of plant development and under different conditions. The ability of this organelle to perform a range of functions depends on the time‐ and process‐dependent import of particular enzymes that enable biochemical reactions to take place inside peroxisomes. While it is important to recruit the right enzymes, it is also important to remove obsolete or damaged enzymes through the turnover of specific proteins. In some cases, degradation of the entire peroxisome is carried out by the process of autophagy, which helps to maintain quality control by removing damaged/dysfunctional/obsolete peroxisomes. Therefore, the diversification of plant peroxisomes for different cellular requirements is achieved through targeted turnover and import of specific enzymes. This article discusses the possible mechanisms and factors involved in functional remodelling of the plant peroxisome from the young seedling peroxisome to the leaf peroxisome. Functions of peroxisomes found in different developmental stages of the plant are also highlighted. Key Concepts Peroxisomes are single membrane‐bound eukaryotic organelles that perform a wide range of functions and display remarkable metabolic diversity. Peroxisomes do not contain any genetic information and therefore all peroxisomal proteins are imported post‐translationally from the cytosol. Peroxisomes are a major scavenger of hydrogen peroxide and plant peroxisomes are the sole site for β‐oxidation of fatty acids. Protein content of peroxisomes varies in a developmental and functional manner. In young seedlings post‐germination, peroxisomes house glyoxylate cycle enzymes that help to generate energy from oil reserves in the seed. In etiolated mature seedlings, peroxisomes are ‘remodelled’ to perform photorespiration. Peroxisome remodelling is achieved by removing glyoxylate cycle enzymes and importing photorespiration enzymes. Glyoxylate cycle enzymes are removed by turnover either inside or outside peroxisomes by proteases and/or by the turnover of obsolete peroxisomes through autophagy process.