Biology subjects

Jonikas, M.

Publications and source records attributed to Jonikas, M..

4 recordsLinked to original sources

bioRxiv2026

RBMP2 shapes specialized membranes for CO₂ delivery in the pyrenoid condensate

Approximately one-third of global CO2 fixation occurs in the algal pyrenoid, a condensate of the CO2-fixing enzyme Rubisco traversed by membranes that supply it with CO2. In the model alga Chlamydomonas reinhardtii, CO2 is delivered by a specialized central reticulated region of these membranes. Here we define how this region is built and identify RBMP2 as the first factor required for its biogenesis. Loss of RBMP2 prevents reticulated-region formation and impairs pyrenoid-dependent growth. RBMP2 domains perform separable roles in extending membrane tubules toward the pyrenoid center and remodeling them into narrow tubules of the reticulated region. The CO2-releasing carbonic anhydrase CAH3 localizes not only to the reticulated region but also to helical interfaces between tubules and minitubules, which expand in some RBMP2 truncation mutants. Our findings advance the basic understanding of pyrenoid function and establish the pyrenoid as a powerful system for studying membrane remodeling within a phase-separated condensate.

Plant Biology↗

bioRxiv2026

Super-resolution expansion microscopy reveals nanoscale protein domains and CO 2 -dependent remodeling of Chlamydomonas pyrenoid-traversing membranes

Within the algal carbon-assimilating organelle, the pyrenoid, specialized traversing membranes perform the essential function of delivering concentrated CO2 to Rubisco. In Chlamydomonas reinhardtii, these membranes consist of peripheral cylindrical tubules that connect to a central reticulated region. However, due to resolution limitations, the spatial distribution of their structural and functional proteins has remained unclear. Here, we achieve an [~]11-fold improvement in resolution by combining ultrastructure expansion microscopy with super-resolution instantaneous structured illumination microscopy, revealing protein localizations and condition-dependent remodeling of these membranes. At air levels of CO2, the tubule-initiating protein SAGA1 forms narrow rings at the pyrenoid edge, the tubule-extending protein MITH1 surrounds the peripheral tubules, and the putative transporter BST4 surrounds tubules more centrally, suggesting that the cylindrical tubules contain multiple distinct protein domains. The CO2-delivering carbonic anhydrase CAH3 localizes to the inner face of the central reticulated region, suggesting that this region is specialized for CO2 delivery. CAH3 remains in the reticulated region at high CO2, suggesting that the cell maintains a minimal CO2-delivery apparatus even when dispensable. Finally, at high CO2, cylindrical tubule diameter narrows, and MITH1 relocalizes throughout the pyrenoid-traversing membrane network. Together, our study elucidates sub-pyrenoid protein organization and CO2-dependent reorganization.

Plant Biology↗

bioRxiv2024

The Arabidopsis amino acid transporter UmamiT20 confers susceptibility to B. cinerea

O_LIInduction of SWEET sugar transporters by bacterial pathogens via transcription activator-like (TAL) effectors is necessary for successful blight infection of rice, cassava and cotton, - likely providing sugars for bacterial propagation. C_LIO_LIHere, we show that infection of Arabidopsis by the necrotrophic fungus Botrytis cinerea causes increased accumulation of amino acid transporter UmamiT20 mRNA in leaves. UmamiT20 protein accumulates in leaf veins surrounding the lesions after infection. Consistent with a role during infection, umamiT20 knock-out mutants were less susceptible to B. cinerea. C_LIO_LIFunctional assays demonstrate that UmamiT20 mediates amino acid transport of a wide range of amino acid substrates. C_LIO_LIPathogen-induced UmamiT20 mRNA and protein accumulation support the hypothesis that transporter-mediated pathogen susceptibility is not unique to SWEETs in bacterial blight of rice but also for a necrotrophic fungus and implicate nutrients other than sucrose, i.e., amino acids, in nutrition or nutrient signaling related to immunity. We hypothesize that stacking of mutations in different types of susceptibility-related nutrient carriers to interfere with access to several nutrients may enable engineering robust pathogen resistance in a wide range of plant-pathogen systems. C_LI Lay AbstractPathogens infect plants to gain access to their nutrient resources, enabling the pathogens to cause disease and reproduce efficiently. Here we find that an amino acid transporter constitutes a susceptibility factor for the fungal pathogen B. cinerea.

plant biology↗

bioRxiv2022

A Chloroplast Protein Atlas Reveals Novel Structures and Spatial Organization of Biosynthetic Pathways

Chloroplasts are eukaryotic photosynthetic organelles that drive the global carbon cycle. Despite their importance, our understanding of their protein composition, function, and spatial organization remains limited. Here, we determined the localizations of 1,032 candidate chloroplast proteins by using fluorescent protein tagging in the model alga Chlamydomonas reinhardtii. The localizations provide insights into the functions of hundreds of poorly-characterized proteins, including identifying novel components of nucleoids, plastoglobules, and the pyrenoid. We discovered and further characterized novel organizational features, including eleven chloroplast punctate structures, cytosolic crescent structures, and diverse unexpected spatial distributions of enzymes within the chloroplast. We observed widespread protein targeting to multiple organelles, identifying proteins that likely function in multiple compartments. We also used machine learning to predict the localizations of all Chlamydomonas proteins. The strains and localization atlas developed here will serve as a resource to enable studies of chloroplast architecture and functions. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/493820v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@19c871eorg.highwire.dtl.DTLVardef@16ac46corg.highwire.dtl.DTLVardef@859b7dorg.highwire.dtl.DTLVardef@1a3446e_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LI1,032 candidate chloroplast proteins localized by fluorescent tagging. C_LIO_LIThis protein atlas reveals novel chloroplast structures, functional regions, and components. C_LIO_LIPrevalent dual-organelle localization suggests extensive cross-compartment coordination. C_LIO_LIAtlas-trained machine learning predicts localizations of all C. reinhardtii proteins. C_LI

plant biology↗