VQ1 and VQ10 are largely unstructured homologous proteins with a significant potential for protein-protein interactions. Yeast two-hybrid (Y2H) analysis confirmed that both proteins interact not only with themselves and each other but also with other VQ and WRKY proteins. Screening an Arabidopsis Y2H library with VQ1 as bait identified 287 interacting proteins. Validation of the screening confirmed that interactions with VQ1 also occurred with VQ10, supporting their functional homology. Although VQ1 or VQ10 proteins do not localize in plastids, 47 VQ1-targets were found to be plastidial proteins. In planta interaction with the isoprenoid biosynthetic enzyme 1-deoxy-D-xylulose-5-phosphate synthase (DXS) was confirmed by co-immunoprecipitation. DXS oligomerizes through redox-regulated intermolecular disulfide bond formation, and the interaction with VQ1 or VQ10 do not involve their unique C residues. The VQ-DXS protein interaction did not alter plastid DXS localization or its oligomerization state. Although plants with enhanced or reduced VQ1 and VQ10 expression did not exhibit significantly altered levels of isoprenoids compared to wild-type plants, they did display significantly improved or diminished photosynthesis efficiency, respectively.

Plastid retrograde signaling plays a key role in coordinating the expression of plastid genes and photosynthesis-associated nuclear genes (PhANGs). Although plastid retrograde signaling can be substantially compromised by mitochondrial dysfunction, it is not yet clear whether specific mitochondrial factors are required to regulate plastid retrograde signaling. Here, we show that mitochondrial ATP synthase beta-subunit mutants with decreased ATP synthase activity are impaired in plastid retrograde signaling in Arabidopsis thaliana. Transcriptome analysis revealed that the expression levels of PhANGs were significantly higher in the mutants affected in the AT5G08670 gene encoding the mitochondrial ATP synthase beta-subunit, compared to wild-type (WT) seedlings when treated with lincomycin (LIN) or norflurazon (NF). Further studies indicated that the expression of nuclear genes involved in chloroplast and mitochondrial retrograde signaling was affected in the AT5G08670 mutant seedlings treated with LIN. These changes might be linked to the modulation of some transcription factors (TFs), such as LHY (Late Elongated Hypocotyl), PIF (Phytochrome-Interacting Factors), MYB, WRKY, and AP2/ERF (Ethylene Responsive Factors). These findings suggest that the activity of mitochondrial ATP synthase significantly influences plastid retrograde signaling.

The unprenylated benzoquinones 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone), 2-chloro-1,4-benzoquinone (CBQ), 2,6-dimethyl-1,4-benzoquinone (DMBQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and 2,6-dimethoxy-1,4-benzoquinone (DMOBQ) were tested as putative antimetabolites of plastoquinone-9, a vital electron and proton carrier of oxygenic phototrophs. Duroquinone and CBQ were the most effective at inhibiting the growth of the cyanobacterium Synechocystis sp. PCC 6803 either in photomixotrophic or photoautotrophic conditions. Duroquinone, a close structural analog of the photosynthetic inhibitor methyl-plastoquinone-9, was found to possess genuine bactericidal activity towards Synechocystis at a concentration as low as 10 μM, while at the same concentration CBQ acted only as a mild bacteriostat. In contrast, only duroquinone displayed marked cytotoxicity in axenically-grown Arabidopsis, resulting in damages to photosystem II and hindered net CO2 assimilation. Metabolite profiling targeted to photosynthetic cofactors and pigments indicated that in Arabidopsis duroquinone does not directly inhibit plastoquinone-9 biosynthesis. Taken together, these data indicate that duroquinone offers prospects as an algicide and herbicide.

Carotenoids, natural tetraterpenoids found abundantly in plants, contribute to the diverse colors of plant non-photosynthetic tissues and provide fragrance through their cleavage products, which also play crucial roles in plant growth and development. Understanding the synthesis, degradation, and storage pathways of carotenoids and identifying regulatory factors represents a significant strategy for enhancing plant quality. Chromoplasts serve as the primary plastids responsible for carotenoid accumulation, and their differentiation is linked to the levels of carotenoids, rendering them a subject of substantial research interest. The differentiation of chromoplasts involves alterations in plastid structure and protein import machinery. Additionally, this process is influenced by factors such as the ORANGE (OR) gene, Clp proteases, xanthophyll esterification, and environmental factors. This review shows the relationship between chromoplast and carotenoid accumulation by presenting recent advances in chromoplast structure, the differentiation process, and key regulatory factors, which can also provide a reference for rational exploitation of chromoplasts to enhance plant quality.

Stramenopile algae contribute significantly to global primary productivity, and one class, Eustigmatophyceae, is increasingly studied for applications in high-value lipid production. Yet much about their basic biology remains unknown, including the nature of an enigmatic, pigmented globule found in vegetative cells. Here, we present an in-depth examination of this \"red body,\" focusing on Nannochloropsis oceanica. During the cell cycle, the red body forms adjacent to the plastid, but unexpectedly it is secreted and released with the autosporangial wall following cell division. Shed red bodies contain antioxidant ketocarotenoids, and overexpression of a beta-carotene ketolase results in enlarged red bodies. Infrared spectroscopy indicates long-chain, aliphatic lipids in shed red bodies and cell walls, and UHPLC-HRMS detects a C32 alkyl diol, a potential precursor of algaenan, a recalcitrant cell wall polymer. We propose that the red body transports algaenan precursors from plastid to apoplast to be incorporated into daughter cell walls.

Dinophysis dinoflagellates are predators of Mesodinium ciliates, from which they retain only the plastids of cryptophyte origin. The absence of nuclear photosynthetic cryptophyte genes in Dinophysis raises intriguing physiological and evolutionary questions regarding the functional dynamics of these temporary kleptoplastids within a foreign cellular environment. In an experimental setup including two light conditions, the comparative analysis with Mesodinium rubrum and the cryptophyte Teleaulax amphioxeia revealed that Dinophysis acuminata possessed a smaller and less dynamic functional photosynthetic antenna for green light, a function performed by phycoerythrin. We showed that the lack of the cryptophyte nucleus prevented the synthesis of the phycoerythrin α subunit, thereby hindering the formation of a complete phycoerythrin in Dinophysis. In particular, biochemical analyses showed that Dinophysis acuminata synthesized a poorly stable, incomplete phycoerythrin composed of chromophorylated β subunits, with impaired performance. We show that, consequently, a continuous supply of new plastids is crucial for growth and effective photoacclimation in this organism. Transcriptome analyses revealed that all examined strains of Dinophysis spp. have acquired the cryptophyte pebA and pebB genes through horizontal gene transfer, suggesting a potential ability to synthesize the phycobilin pigments bound to the cryptophyte phycoerythrin. By emphasizing that a potential long-term acquisition of the cryptophyte plastid relies on establishing genetic independence for essential functions such as light harvesting, this study highlights the intricate molecular challenges inherent in the enslavement of organelles and the processes involved in the diversification of photosynthetic organisms through endosymbiosis.

Plant cells harbor two membrane-bound organelles containing their own genetic material-plastids and mitochondria. Although the two organelles coexist and coevolve within the same plant cells, they differ in genome copy number, intracellular organization, and mode of segregation. How these attributes affect the time to fixation or, conversely, loss of neutral alleles is currently unresolved. Here, we show that mitochondria and plastids share the same mutation rate, yet plastid alleles remain in a heteroplasmic state significantly longer compared with mitochondrial alleles. By analyzing genetic variants across populations of the marine flowering plant Zostera marina and simulating organelle allele dynamics, we examine the determinants of allele segregation and allele fixation. Our results suggest that the bottlenecks on the cell population, e.g. during branching or seeding, and stratification of the meristematic tissue are important determinants of mitochondrial allele dynamics. Furthermore, we suggest that the prolonged plastid allele dynamics are due to a yet unknown active plastid partition mechanism. The dissimilarity between plastid and mitochondrial novel allele fixation at different levels of organization may manifest in differences in adaptation processes. Our study uncovers fundamental principles of organelle population genetics that are essential for further investigations of long-term evolution and molecular dating of divergence events.

The root endophytic fungus Serendipita indica establishes beneficial symbioses with a broad spectrum of plants and enhances host resilience against biotic and abiotic stresses. However, little is known about the mechanisms underlying S. indica-mediated plant protection. Here, we report S. indica effector (SIE) 141 and its host target CDSP32, a conserved thioredoxin-like protein, and underlying mechanisms for enhancing pathogen resistance and abiotic salt tolerance in Arabidopsis thaliana. SIE141 binding interfered with canonical targeting of CDSP32 to chloroplasts, leading to its re-location into the plant nucleus. This nuclear translocation is essential for both their interaction and resistance function. Furthermore, SIE141 enhanced oxidoreductase activity of CDSP32, leading to CDSP32-mediated monomerization and activation of NON-EXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1), a key regulator of systemic resistance. Our findings provide functional insights on how S. indica transfers well-known beneficial effects to host plants and indicate CDSP32 as a genetic resource to improve plant resilience to abiotic and biotic stresses.

Through the shikimate pathway, a massive metabolic flux connects the central carbon metabolism with the synthesis of chorismate, the common precursor of the aromatic amino acids phenylalanine, tyrosine, and tryptophan, as well as other compounds, including salicylate or folate. The alternative metabolic channeling of chorismate involves a key branch-point, finely regulated by aromatic amino acid levels. Chorismate mutase catalyzes the conversion of chorismate to prephenate, a precursor of phenylalanine and tyrosine and thus a vast repertoire of fundamental derived compounds, such as flavonoids or lignin. The regulation of this enzyme has been addressed in several plant species, but no study has included conifers or other gymnosperms, despite the importance of the phenolic metabolism for these plants in processes such as lignification and wood formation. Here, we show that maritime pine (Pinus pinaster Aiton) has two genes that encode for chorismate mutase, PpCM1 and PpCM2. Our investigations reveal that these genes encode plastidial isoenzymes displaying activities enhanced by tryptophan and repressed by phenylalanine and tyrosine. Using phylogenetic studies, we have provided new insights into the possible evolutionary origin of the cytosolic chorismate mutases in angiosperms involved in the synthesis of phenylalanine outside the plastid. Studies based on different platforms of gene expression and co-expression analysis have allowed us to propose that PpCM2 plays a central role in the phenylalanine synthesis pathway associated with lignification.

In land plants plastid type differentiation occurs concomitantly with cellular differentiation and the transition from one type to another is under developmental and environmental control. Plastid dynamism is based on a bilateral communication between plastids and nucleus through anterograde and retrograde signaling. Signaling occurs through the interaction with specific phytohormones (abscisic acid, strigolactones, jasmonates, gibberellins, brassinosteroids, ethylene, salicylic acid, cytokinin and auxin). The review is focused on the modulation of plastid capabilities at both transcriptional and post-translational levels at the crossroad between development and stress, with a particular attention to the chloroplast, because the most studied plastid type. The role of plastid-encoded and nuclear-encoded proteins for plastid development and stress responses, and the changes of plastid fate through the activity of stromules and plastoglobules, are discussed. Examples of plastid dynamism in response to soil stress agents (salinity, lead, cadmium, arsenic, and chromium) are described. Albinism and root greening are described based on the modulation activities of auxin and cytokinin. The physiological and functional responses of the sensory epidermal and vascular plastids to abiotic and biotic stresses along with their specific roles in stress sensing are described together with their potential modulation of retrograde signaling pathways. Future research perspectives include an in-depth study of sensory plastids to explore their potential for establishing a transgenerational memory to stress. Suggestions about anterograde and retrograde pathways acting at interspecific level and on the lipids of plastoglobules as a novel class of plastid morphogenic agents are provided.