Mitochondria fulfill a wide range of metabolic functions in addition to the synthesis of ATP and contain a diverse array of proteins to perform these functions. Here, we present the unexpected discovery of the presence of the enzymes of glycolysis in a mitochondrial fraction of Arabidopsis cells. Proteomic analyses of this mitochondrial fraction revealed the presence of 7 of the 10 enzymes that constitute the glycolytic pathway. Four of these enzymes (glyceraldehyde-3-P dehydrogenase, aldolase, phosphoglycerate mutase, and enolase) were also identified in an intermembrane space/outer mitochondrial membrane fraction. Enzyme activity assays confirmed that the entire glycolytic pathway was present in preparations of isolated Arabidopsis mitochondria, and the sensitivity of these activities to protease treatments indicated that the glycolytic enzymes are present on the outside of the mitochondrion. The association of glycolytic enzymes with mitochondria was confirmed in vivo by the expression of enolase– and aldolase–yellow fluorescent protein fusions in Arabidopsis protoplasts. The yellow fluorescent protein fluorescence signal showed that these two fusion proteins are present throughout the cytosol but are also concentrated in punctate regions that colocalized with the mitochondrion-specific probe Mitotracker Red. Furthermore, when supplied with appropriate cofactors, isolated, intact mitochondria were capable of the metabolism of 13C-glucose to 13C-labeled intermediates of the trichloroacetic acid cycle, suggesting that the complete glycolytic sequence is present and active in this subcellular fraction. On the basis of these data, we propose that the entire glycolytic pathway is associated with plant mitochondria by attachment to the cytosolic face of the outer mitochondrial membrane and that this microcompartmentation of glycolysis allows pyruvate to be provided directly to the mitochondrion, where it is used as a respiratory substrate.
In contrast to its close homolog PLANT UNCOUPLING MITOCHONDRIAL PROTEIN 1 (UCP1), which is an abundant carrier protein in the mitochondria, UCP2 localizes to the Golgi.
The core role of a journal is to oversee the peer-review and publication of high-standard research articles and reviews. Increasingly, however, journals are seeking to provide added value through the publication of commentaries, interviews and other features. As a society journal, The Plant Journal sees these type of features pieces as an important part of its remit, not only because they enable us to promote the excellent science that we publish, but also because they allow us to build bridges with our audience and to support the research community. TPJ currently publishes a single commentary article per issue in the form of a ‘Research Highlight’ that summarizes a research article and draws out the backstory behind the research. Occasionally, the Editor-in-Chief stirs his pen to write an editorial like this one. But we prefer not to clutter up the journal issues with commentaries and other features. This raises the problem as to where we should publish those additional articles. We felt that the best solution to this problem was to develop a dedicated ‘TPJ Features’ website, and this editorial is to bring to your attention the launch of the site. The process of building and launching the TPJ Features website started back in the summer of 2020 with the recruitment of Alon Cna'ani as the new TPJ Features Editor. Alon is a post-doc with interests in floral scent, plant specialized metabolism and food science. He is currently studying floral scent biology in wild Brassicaceae populations at the Institute of Desert Research, Ben-Gurion University, Israel. For the initial launch of the site, we decided to turn the spotlight onto the TPJ editorial board. If you visit the website, you will find interviews with a long-serving past member of the board (Sheila McCormick, University of California, Berkeley), a long-serving current member (Asaph Aharoni, Weizmann Institute of Science, Israel) and a recently-appointed member (Jianbing Yan, National Key Laboratory of Crop Genetics, Wuhan). All have provided fascinating and highly personal insights of their paths into research, their interests and passions. Alon also interviewed the two TPJ Fellows, Edwige Moyroud (University of Cambridge) and Jake Brunkard (University of Wisconsin-Madison). We will continue to highlight the brilliant editors and associate members of the journal on the Features website. But we also want to engage with the plant sciences research community, and there are several features in the pipeline designed to do just that. The first is a fascinating interview with Tanisha Williams (Bucknell University, Pennsylvania, USA) and Nokwanda Makunga (Stellenbosch University, South Africa) who initiated the #BlackBotanistWeek on social media. If you are interested in contributing to the TPJ features site, either as interviewer or interviewee, or if you’d like to propose a different type of contribution, please contact the Features Editor by email. We are keen to hear from research scientists at any level, but especially would like to hear from early career researchers. The Features Editor will be running a series of ‘day in the life’ pieces featuring post-docs and PhD students, so please get in touch if you would like to be featured!
This protocol describes the isolation of tonoplast vesicles from tomato fruit. The vesicles isolated using this procedure are of sufficiently high purity for downstream proteomic analysis whilst remaining transport competent for functional assays. The methodology was used to study the transport of amino acids during tomato fruit ripening (Snowden et al., 2015) and based on the procedure used by Betty and Smith (Bettey and Smith, 1993). Such vesicles may be useful in further studies into the dynamic transfer of metabolites across the tonoplast for storage and metabolism during tomato fruit development.
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