Visualization of microbodies in Chlamydomonas reinhardtii

Abstract

In Chlorophycean algal cells, these organelles are generally called microbodies because they lack the enzymes found in the peroxisomes of higher plants. Microbodies in some algae contain fewer enzymes than the peroxisomes of higher plants, and some unicellular green algae in Chlorophyceae such as Chlamydomonas reinhardtii do not possess catalase, an enzyme commonly found in peroxisomes. Thus, whether microbodies in Chlorophycean algae are similar to the peroxisomes of higher plants, and whether they use a similar transport mechanism for the peroxisomal targeting signal (PTS), remain unclear. To determine whether the PTS is present in the microbodies of Chlorophycean algae, and to visualize the microbodies in Chlamydomonas cells, we examined the sub-cellular localization of green fluorescent proteins (GFP) fused to several PTS-like sequences. We detected GFP compartments that were spherical with a diameter of 0.3-1.0 μm in transgenic Chlamydomonas. Comparative analysis of the character of GFP-compartments observed by fluorescence microscopy and that of microbodies by electron microscopy indicated that the compartments were one and the same. The result also showed that the microbodies in Chlorophycean cells have a similar transport mechanism to that of peroxisomes of higher plants.

Down‐regulation of catalase activity allows transient accumulation of a hydrogen peroxide signal in Chlamydomonas reinhardtii

“…While higher plants contain three catalase genes, only one catalase gene (CAT1, A8J537, UNIPROT) is present in the Chlamydomonas genome. In higher plants, catalases are localized to peroxisomes, while in C. reinhardtii , which lacks leaf‐like peroxisomes, the enzyme is most likely located in cytosolic microbodies that were visualized by sub‐cellular localization of green fluorescent proteins fused to several putative Chlamydomonas peroxisomal targeting sequences (Hayashi & Shinozaki ). Figure shows that inactivation of catalase activity may be related to a conformational change.…”

Evolution of the biochemistry of the photorespiratory C2 cycle

“…Since the mechanism for protein targeting to peroxisomes appears to be conserved at least in green algae (Shinozaki et al . ; Hayashi & Shinozaki ), the presence of peroxisome‐targeting signals (PTS), either a C‐terminal tripeptide or an N‐terminal nonapeptide, can be used to judge the localisation of photorespiratory enzymes among algae. As mentioned above, putative orthologues of most photorespiratory enzymes can be found in many of the sequenced microalgae, many of which contain predicted PTSs (Sigrun Reumann, unpublished data).…”

Putative role of the malate valve enzyme NADP–malate dehydrogenase in H 2 O 2 signalling in Arabidopsis

“…In the C. reinhardtii genome, only one catalase gene (CAT1, A8J537, UNIPROT) is present, whereas higher plants contain three catalase genes (CAT1-3 in Arabidopsis). In higher plants, catalases are localized in peroxisomes, whereas in C. reinhardtii, which lacks leaf-like peroxisomes, the enzyme is most likely to be located in cytosolic microbodies that were visualized by subcellular localization of green fluorescent proteins fused to several putative Chlamydomonas peroxisomal targeting sequences [21]. According to our hypothesis (figure 1a), light stress increases the production of ROS ( In mammalian cells, the 'floodgate hypothesis' [22] posits that an overoxidation of the peroxidatic cysteine of 2-Cys peroxiredoxin (Prx) to the sulfinate form, and its subsequent slow reduction by sulfiredoxin [23,24], leads to a peak in H 2 O 2 that allows this ROS to take on a signalling role.…”