Biology subjects

Barreto, P.

Publications and source records attributed to Barreto, P..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial malate metabolism acts as a control hub for photosynthesis and carbon-nitrogen balance in Arabidopsis

Malate is a central metabolite in plant energy metabolism and biosynthesis and serves as a major carrier of carbon and reducing equivalents between chloroplasts, the cytosol, and mitochondria. However, how individual malate-converting systems contribute to physiology in specific subcellular compartments remains incompletely understood. Here, we investigated the impact of combined loss of mitochondrial malate dehydrogenase (MDH) and NAD-dependent malic enzyme (NAD-ME) activity in Arabidopsis thaliana by integrating reverse genetics, physiological analyses, transcriptomics, quantitative proteomics, and metabolite profiling. Specifically, we generated triple mutants (mdh1xme1xme2) lacking the predominant mitochondrial isoform MDH1 together with both NAD-ME subunits, thereby reducing overall mitochondrial malate conversion capacity. By growing plants under contrasting photoperiod and irradiance regimes to vary photosynthetic demand on malate-linked fluxes, we uncovered a conditional phenotype that was most pronounced under short-day/low-light conditions. Under these conditions, mdh1xme1xme2 exhibited impaired growth and photosynthetic performance, accompanied by cytosolic redox imbalance and altered chloroplast ultrastructure. Transcriptomic profiling revealed that low light unmasks a dawn-phase bottleneck in establishing photosynthetic and redox homeostasis. Consistent with this, the low-light plastid proteome revealed a reallocation away from chloroplast translation and photosynthetic capacity toward proteome maintenance, photoprotection/repair, and iron/ROS management, consistent with a protective acclimation state that nevertheless constrains carbon gain under energy limitation. Low light also triggered C/N imbalance and ammonium accumulation in the mutants. In contrast, increasing irradiance or extending the photoperiod largely alleviated these defects. Together, our results identified mitochondrial malate conversion capacity as a key control point coupling respiratory energy supply and redox homeostasis to photosynthetic metabolism when photosynthetic energy input is limiting.

plant biology↗

bioRxiv2025

Advanced illumination-imaging reveals photosynthesis-triggered pH, ATP and NAD redox signatures across plant cell compartments

Photosynthesis provides energy and organic substrates to most life. In plants, photosynthesis dominates chloroplast physiology but represents only a fraction of the tightly interconnected metabolic network that spans the entire cell. Here, we explore how photosynthetic activity affects energy physiology within and beyond the chloroplast. We developed a new standard for the live-monitoring of subcellular energy physiology by combining confocal imaging of genetically encoded fluorescent protein biosensors with advanced on-stage illumination technology to investigate pH, MgATP2- and NADH/NAD+ dynamics at dark-light transitions in Arabidopsis mesophyll cells. Our findings reveal a stromal alkalinization signature induced by photosynthetic proton pumping, extending to the cytosol and mitochondria as an alkalinization wave. Photosynthesis leads to increased MgATP2- levels in both the stroma and cytosol. Additionally, we observed reduction of the NAD pool driven by photosynthesis-derived electron export. Arabidopsis lines defective in chloroplast NADP- and mitochondrial NAD-dependent malate dehydrogenases show more reduced cytosolic NAD redox status even in darkness, highlighting the involvement of chloroplasts and mitochondria in shaping cytosolic redox metabolism via malate metabolism. Our study sets a novel methodological standard for precision live-monitoring of photosynthetic cell physiology. Applying this technology reveals signatures of photosynthetic physiology within and beyond the chloroplast with unprecedented resolution. Those signatures link photosynthetic activity and the fundamental biochemical functions of phototrophic cells. Significance statementBy applying novel live microscopy monitoring using fluorescent protein biosensors in plant cells, we reveal that dark-light transitions trigger profound re-orchestration of subcellular pH, ATP and NAD redox physiology not limited to chloroplasts but extending into the cytosol and the mitochondria.

plant biology↗

bioRxiv2024

Early seedling development in dark conditions is directly controlled by plastids through the GUN1-dependent plastid retrograde pathway

In dark growth conditions, seedlings develop specific features such as an elongated hypocotyl, a tightly folded apical hook, and non-green cotyledons. This dark-specific process, known as skotomorphogenesis, relies primarily on mitochondria and eventually etioplasts for energy. Our previous research shows that skotomorphogenesis is reprogrammed in response to mitochondrial and plastidial dysfunction. Even though the direct link between mitochondria and skotomorphogenesis was described, the impact of plastid dysfunction on early development could not be separated from mitochondrial stress. In this study, we aim to determine the direct connection between plastid functionality and skotomorphogenic response. In this situation, we analyze the phenotypic, molecular, and metabolic effects of treating etiolated seedlings using lincomycin and spectinomycin, which target plastid translation. Our results with the lincomycin treatment highlight the direct role of plastids in the control of early development, even in dark growth conditions, in the absence of any photosynthetic activity, and without the involvement of mitochondrial intermediates. Additionally, our findings suggest that GUN1 plays a regulatory role in regulating nuclear gene expression in response to plastid translation inhibition. Thanks to our study, we can now build a more precise model proposing a straight link between the reprogramming of early development and the dysfunction of plastids in dark-growth conditions. Significance statementIn underground germination conditions, seedlings follow a dark-specific development program, called skotomorphogenesis, that is required for their efficient emergence from the soil. Our study demonstrates that plastids play a crucial role in controlling skotomorphogenesis, even in the absence of photosynthetic activity and without affecting mitochondrial function, and therefore we propose that regulation of etioplast functions might contribute to the adaptation of seedling development to constraining environmental conditions.

plant biology↗

bioRxiv2023

PLANT UNCOUPLING MITOCHONDRIAL PROTEIN 2 localizes to the Golgi

Mitochondria act as cellular hubs of energy transformation and metabolite conversion in most eukaryotes. Plant mitochondrial electron transport chains are particularly flexible, featuring alternative components, such as ALTERNATIVE NAD(P)H DEHYDROGENASES and ALTERNATIVE OXIDASES (AOXs), that can bypass proton translocation steps. PLANT UNCOUPLING MITOCHONDRIAL PROTEINS (named PUMPs or plant UCPs) have been identified in plants as homologues of mammalian Uncoupling Proteins (UCPs), and their biochemical and physiological roles have been investigated in the context of mitochondrial energy metabolism. To dissect UCP function in Arabidopsis, the two most conserved (UCP1 and UCP2) have been targeted in recent work by combining mutant lines to circumvent potential functional redundancy in vivo. Such approaches rely on the assumption that both proteins reside in the inner mitochondrial membrane as a prerequisite for functional redundancy. Yet, contradicting results have been reported on UCP2 localization in plants. Here we provide evidence that, conversely to UCP1, which is an abundant inner mitochondrial membrane protein, UCP2 localizes to the Golgi rather than to mitochondria. Based on multiple lines of new and prior evidence, we summarize the consensus view that we have reached and provide an example of how open, critical exchange within the research community is able to constructively address ambiguities. Our observations and considerations provide direction to the ongoing discussion about the functions of UCP proteins. They further offer new perspectives for the study of Golgi membrane transport and subcellular targeting principles of membrane proteins. Since 20 to 30 % of genes in plant genomes are predicted to encode transmembrane proteins and the function of most of those proteins has not been experimentally investigated, we highlight the importance of using independent evidence for localization as a prerequisite for understanding physiological function of membrane proteins.

plant biology↗