Kroth, P. G. | Search bioRxiv

bioRxiv2024

Both major xanthophyll cycles present in nature can provide Non-Photochemical Quenching in the model diatom Phaeodactylum tricornutum

Xanthophyll cycling contributes to photoprotection by regulating Non-Photochemical Quenching (NPQ). While most photosynthetic eukaryotes including land plants use the violaxanthin cycle, some algae like diatoms and haptophytes rely on the diadinoxanthin cycle for photoprotection. These algae also contain minor amounts of violaxanthin cycle pigments, serving as precursors in xanthophylls biosynthesis. Both cycles are catalyzed by the enzymes violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). Here, we characterized the role of VDE and different ZEP-encoding paralogs (ZEP2 and ZEP3) in the model diatom Phaeodactylum tricornutum. While knockout of VDE and ZEP3 significantly impaired the diadinoxanthin cycle, lack of ZEP2 led to sustained accumulation of the violaxanthin cycle instead of diadinoxanthin cycle pigments under high irradiance, with no negative effect on NPQ capacity. We demonstrate that both major xanthophyll cycles present in nature can function with comparable efficiency within the same species, offering a new perspective on the evolution of xanthophyll-mediated photoprotection.

plant biology↗

bioRxiv2018

Mitochondrial targeting of glycolysis in a major lineage of eukaryotes

Glycolysis is a major cytosolic catabolic pathway that provides ATP for many organisms1. Mitochondria play an even more important role in the provision of additional cellular ATP for eukaryotes2. Here, we show that in many stramenopiles, the C3 part of glycolysis is localised in mitochondria. We discovered genuine mitochondrial targeting signals on the six last enzymes of glycolysis. These targeting signals are recognised and sufficient to import GFP into mitochondria of a heterologous host. Analysis of eukaryotic genomes identified these targeting signals on many glycolytic C3 enzymes in a large group of eukaryotes found in the SAR supergroup3, in particular the stramenopiles. Stramenopiles, or heterokonts, are a large group of ecologically important eukaryotes that includes multi- and unicellular algae such as kelp and diatoms, but also economically important oomycete pathogens such as Phytophthora infestans. Confocal immunomicroscopy confirmed the mitochondrial location of glycolytic enzymes for the human parasite Blastocystis. Enzyme assays on cellular fractions confirmed the presence of the C3 part of glycolysis in Blastocystis mitochondria. These activities are sensitive to treatment with proteases and Triton X-100 but not proteases alone. Our work clearly shows that core cellular metabolism is more plastic than previously imagined and suggests new strategies to combat stramenopile pathogens such as the causative agent of late potato blight, P. infestans.

evolutionary biology↗