Biochemical Society Annual Symposium No. 77 Peroxisome division and proliferation in plants Kyaw Aung*†, Xinchun Zhang*‡ and Jianping Hu*†‡ 1 *MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, U.S.A., †Plant Biology Department, Michigan State University, East Lansing, MI 48824, U.S.A., and ‡Genetics Graduate Program, Michigan State University, East Lansing, MI 48824, U.S.A. Abstract Peroxisomes are eukaryotic organelles with crucial functions in development. Plant peroxisomes participate in various metabolic processes, some of which are co-operated by peroxisomes and other organelles, such as mitochondria and chloroplasts. Defining the complete picture of how these essential organelles divide and proliferate will be instrumental in understanding how the dynamics of peroxisome abundance contribute to changes in plant physiology and development. Research in Arabidopsis thaliana has identified several evolutionarily conserved major components of the peroxisome division machinery, including five isoforms of PEROXIN11 proteins (PEX11), two dynamin-related proteins (DRP3A and DRP3B) and two FISSION1 proteins (FIS1A/BIGYIN and FIS1B). Recent studies in our laboratory have also begun to uncover plant-specific factors. DRP5B is a dual-localized protein that is involved in the division of both chloroplasts and peroxisomes, representing an invention of the plant/algal lineage in organelle division. In addition, PMD1 (peroxisomal and mitochondrial division 1) is a plant-specific protein tail anchored to the outer surface of peroxisomes and mitochondria, mediating the division and/or positioning of these organelles. Lastly, light induces peroxisome proliferation in dark-grown Arabidopsis seedlings, at least in part, through activating the PEX11b gene. The far-red light receptor phyA (phytochrome A) and the transcription factor HYH (HY5 homologue) are key components in this signalling pathway. In summary, pathways for the division and proliferation of plant peroxisomes are composed of conserved and plant-specific factors. The sharing of division proteins by peroxisomes, mitochondria and chloroplasts is also suggesting possible co-ordination in the division of these metabolically associated plant organelles. Introduction Peroxisomes exist in almost all eukaryotic cells. These small organelles, 0.1–1 μm in diameter, are delimited by single membranes and do not contain their own genome. However, they perform diverse and crucial metabolic functions, including fatty acid metabolism through β - oxidation and degradation of ROS (reactive oxygen species), such as H 2 O 2 [1]. Peroxisome disorders in humans are caused by impaired biogenesis or function of peroxisomes and can lead to death during infancy or early childhood [2]. Peroxisomes are also essential to plant development, resulting in embryonic lethality when functions of core proteins required for peroxisome biogenesis are disrupted. In addition to lipid metabolism and H 2 O 2 degradation, other pathways and functions demonstrated or indicated to be mediated by plant peroxisomes include photorespiration, the glyoxylate cycle, jasmonic acid biosynthesis, IBA (indole- 3-butyric acid) metabolism, signalling and plant–pathogen interactions [3–5]. In total, 85 and 61 peroxisomal genes have been identified in humans and Saccharomyces cerevisiae Key words: Arabidopsis, dynamin-related protein 5B (DRP5B), light, mitochondrion, peroxisomal and mitochondrial division 1 (PMD1), peroxisome division and proliferation. Abbreviations used: BiFC, bimolecular fluorescence complementation; CFP, cyan fluorescent protein; CHUP1, chloroplast unusual positioning protein 1; co-IP, co-immunoprecipitation; C-TA, C-terminal tail-anchored; DRP, dynamin-related protein; FIS1, FISSION1; GFP, green fluorescent protein; HYH, HY5 homologue; Mff, mitochondrial fission factor; PEX11, PEROXIN11; phyA, phytochrome A; PTS1, peroxisome targeting signal type 1; siRNA, small interfering RNA; TPR, tetratricopeptide repeat; YFP, yellow fluorescent protein. 1 To whom correspondence should be addressed (email huji@msu.edu). respectively [1], in contrast with the over 130 genes validated to date to encode peroxisomal proteins in Arabidopsis (http://www.peroxisome.msu.edu/). This difference in per- oxisomal proteome size may suggest that plant peroxisomes house more pathways and perform more complex functions compared with peroxisomes from yeasts and mammals. Upon developmental, metabolic and environmental changes, peroxisomes are capable of varying their morpho- logy, abundance and content to adapt to the new conditions. It is commonly believed that, besides arising de novo from subdomains of the ER (endoplamic reticulum), peroxisomes can also multiply via division. Division and proliferation (i.e. induced division) both follow the events of peroxisome elongation/growth/tubulation, membrane constriction and fission, resulting in the duplication or multiplication of peroxisomes. A number of components of the peroxisome division/proliferation machineries have been identified from the fungal and animal kingdoms [6–9]; dissection of the molecular events underlying these processes in plants has also begun in recent years. Three evolutionarily conserved components in the peroxisome division machinery Using the reference plant species Arabidopsis thaliana, several proteins or protein families involved in the division/proliferation of peroxisomes have been identified Biochem. Soc. Trans. (2010) 38, 817–822; doi:10.1042/BST0380817 C  The Authors Journal compilation C  2010 Biochemical Society 817