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Maintenance of water homeostasis is a fundamental cellular process required by all living organisms. Here, we use the single-celled green alga Chlamydomonas reinhardtii to establish a foundational understanding of osmotic-stress signaling pathways through transcriptomics, phosphoproteomics, and functional genomics approaches. Comparison of pathways identified through these analyses with yeast and Arabidopsis allows us to infer their evolutionary conservation and divergence across these lineages. 76 genes, acting across diverse cellular compartments, were found to be important for osmotic-stress tolerance in Chlamydomonas through their functions in cytoskeletal organization, potassium transport, vesicle trafficking, mitogen-activated protein kinase and chloroplast signaling. We show that homologs for five of these genes have conserved functions in stress tolerance in Arabidopsis and reveal a novel PROFILIN-dependent stage of acclimation affecting the actin cytoskeleton that ensures tissue integrity upon osmotic stress. This study highlights the conservation of the stress response in algae and land plants, and establishes Chlamydomonas as a unicellular plant model system to dissect the osmotic stress signaling pathway.

Summary: Chloroplasts play a crucial role in plant defense against pathogens, making them primary targets for pathogen effectors that suppress host immunity. This study characterizes the Plasmopara viticola CRN‐like effector, PvCRN20, which interacts with DEG5 in the cytoplasm but not with its interacting protein, DEG8, which is located in the chloroplast.By transiently overexpressing in tobacco leaves, we show that PvCRN20 could inhibit INF1‐ and Bax‐triggered cell death. Constitutive expression of PvCRN20 suppresses the accumulation of reactive oxygen species (ROS) and promotes pathogen colonization. PvCRN20 reduces DEG5 entry into chloroplasts, thereby disrupting DEG5 and DEG8 interactions in chloroplasts.Overexpression of VvDEG5 and VvDEG8 induces ROS accumulation and enhances grapevine resistance to P. viticola, whereas knockout of VvDEG8 represses ROS production and promotes P. viticola colonization. Consistently, ectopic expression of VvDEG5 and VvDEG8 in tobacco promotes chloroplast‐derived ROS accumulation, whereas co‐expression of PvCRN20 counteracted this promotion by VvDEG5. Therefore, DEG5 is essential for the virulence function of PvCRN20. Although PvCRN20 is located in both the nucleus and cytoplasm, only cytoplasmic PvCRN20 suppresses plant immunity and promotes pathogen infection.Our results reveal that PvCRN20 dampens plant defenses by repressing the chloroplast import of DEG5, thus reducing host ROS accumulation and facilitating pathogen colonization. [ABSTRACT FROM AUTHOR]

The microspectrophotometer/microspectrofluorimeter was used to find the azulenes on the intact surface of 30 allelopathic and medicinal plant species growing in moderate or drought climatic conditions. Here in the maxima range of 580-620 nm, peculiar to blue pigments (azulenes), were clearly observed. The pigments were found in blue or silver leaves (needles) or plant parts (petioles, flowers and pollen). The peaks 590-610 nm, characteristic to azulenes were also observed in the absorbance spectra of ethanolic 10 min -extracts from the leaf surface, and 24 h - extracts from whole leaves. Among plants studied, the pigments were first observed in 14 terrestrial species (Anthriscus sylvestris, Lolium perenne, Petasites spurius, Phlomis tuberosa, Crambe maritima, Seseli gummiferum, Filipendula ulmaria, Echinocystis lobata, Colutea cilica, Rhus coriaria, Quercus pubescens, Pinus brutia and 2 algae (Chara vulgaris and Spirogyra sp.) use of spectral methods is recommended to search new azulene-containing species for pharmacy, agriculture and ecology. [ABSTRACT FROM AUTHOR]

C2 photosynthesis is a photosynthetic pathway in which photorespiratory CO2 release and refixation are enhanced in leaf bundle sheath (BS) tissues. The evolution of C2 photosynthesis has been hypothesized to be a major step in the origin of C4 photosynthesis, highlighting the importance of studying C2 evolution. In this study, physiological, anatomical, ultrastructural, and immunohistochemical properties of leaf photosynthetic tissues were investigated in six non‐C4Tribulus species and four C4Tribulus species. At 42°C, T. cristatus exhibited a photosynthetic CO2 compensation point in the absence of respiration (C*) of 21 µmol mol−1, below the C3 mean C* of 73 µmol mol−1. Tribulus astrocarpus had a C* value at 42°C of 55 µmol mol−1, intermediate between the C3 species and the C2T. cristatus. Glycine decarboxylase (GDC) allocation to BS tissues was associated with lower C*. Tribulus cristatus and T. astrocarpus allocated 86% and 30% of their GDC to the BS tissues, respectively, well above the C3 mean of 11%. Tribulus astrocarpus thus exhibits a weaker C2 (termed sub‐C2) phenotype. Increased allocation of mitochondria to the BS and decreased length‐to‐width ratios of BS cells, were present in non‐C4 species, indicating a potential role in C2 and C4 evolution. Summary statement: Physiological, structural, and immunohistochemical analyses of leaf tissues indicate sub‐C2 and C2 character states occurring in Tribulus (Zygophyllaceae). These data reveal novel insights into the mechanisms by which photorespiratory CO2 refixation facilitates the evolution of C4 photosynthesis. [ABSTRACT FROM AUTHOR]

Salinity tolerance requires coordinated responses encompassing salt exclusion in roots and tissue/cellular compartmentation of salt in leaves. We investigated the possible control points for salt ions transport in roots and tissue tolerance to Na+ and Cl– in leaves of two contrasting mungbean genotypes, salt‐tolerant Jade AU and salt‐sensitive BARI Mung‐6, grown in nonsaline and saline (75 mM NaCl) soil. Cryo‐SEM X‐ray microanalysis was used to determine concentrations of Na, Cl, K, Ca, Mg, P, and S in various cell types in roots related to the development of apoplastic barriers, and in leaves related to photosynthetic performance. Jade AU exhibited superior salt exclusion by accumulating higher [Na] in the inner cortex, endodermis, and pericycle with reduced [Na] in xylem vessels and accumulating [Cl] in cortical cell vacuoles compared to BARI Mung‐6. Jade AU maintained higher [K] in root cells than BARI Mung‐6. In leaves, Jade AU maintained lower [Na] and [Cl] in chloroplasts and preferentially accumulated [K] in mesophyll cells than BARI Mung‐6, resulting in higher photosynthetic efficiency. Salinity tolerance in Jade AU was associated with shoot Na and Cl exclusion, effective regulation of Na and Cl accumulation in chloroplasts, and maintenance of high K in root and leaf mesophyll cells. Summary statement: Salinity tolerance in mungbean is related to its ability to intercept Na and Cl in roots, thereby reducing Na and Cl transport to shoot, effectively regulate Na and Cl accumulation in chloroplasts, and maintain high K in root and leaf mesophyll cells. [ABSTRACT FROM AUTHOR]

SUMMARY: HSP90Cs are essential molecular chaperones localized in the plastid stroma that maintain protein homeostasis and assist the import and thylakoid transport of chloroplast proteins. While HSP90C contains all conserved domains as an HSP90 family protein, it also possesses a unique feature in its variable C‐terminal extension (CTE) region. This study elucidated the specific function of this HSP90C CTE region. Our phylogenetic analyses revealed that this intrinsically disordered region contains a highly conserved DPW motif in the green lineages. With biochemical assays, we showed that the CTE is required for the chaperone to effectively interact with client proteins PsbO1 and LHCB2 to regulate ATP‐independent chaperone activity and to effectuate its ATP hydrolysis. The CTE truncation mutants could support plant growth and development reminiscing the wild type under normal conditions except for a minor phenotype in cotyledon when expressed at a level comparable to wild type. However, higher HSP90C expression was observed to correlate with a stronger response to specific photosystem II inhibitor DCMU, and CTE truncations dampened the response. Additionally, when treated with lincomycin to inhibit chloroplast protein translation, CTE truncation mutants showed a delayed response to PsbO1 expression repression, suggesting its role in chloroplast retrograde signaling. Our study therefore provides insights into the mechanism of HSP90C in client protein binding and the regulation of green chloroplast maturation and function, especially under stress conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

SUMMARY Over‐expression (OE) lines for the ER‐tethered NAC transcription factor ANAC017 displayed de‐repression of gun marker genes when grown on lincomycin (lin). RNA‐seq revealed that ANAC017OE2 plants constitutively expressed greater than 40% of the genes induced in wild‐type with lin treatment, including plastid encoded genes ycf1.2 and the gene cluster ndhH‐ndhA‐ndhI‐ndhG‐ndhE‐psaC‐ndhD, documented as direct RNA targets of GUN1. Genes encoding components involved in organelle translation were enriched in constitutively expressed genes in ANAC017OE2. ANAC017OE resulted in constitutive location in the nucleus and significant constitutive binding of ANAC017 was detected by ChIP‐Seq to target genes. ANAC017OE2 lines maintained the ability to green on lin, were more ABA sensitive, did not show photo‐oxidative damage after exposure of de‐etiolated seedlings to continuous light and the transcriptome response to lin were as much as 80% unique compared to gun1‐1. Both double mutants, gun1‐1:ANAC017OE and bzip60:ANAC017OE (but not single bzip60), have a gun molecular gene expression pattern and result in variegated and green plants, suggesting that ANAC017OE may act through an independent pathway compared to gun1. Over‐expression of ANAC013 or rcd1 did not produce a GUN phenotype or green plants on lin. Thus, constitutive ANAC017OE2 establishes an alternative transcriptional program that likely acts through a number of pathways, that is, maintains plastid gene expression, and induction of a variety of transcription factors involved in reactive oxygen species metabolism, priming plants for lin tolerance to give a gun phenotype. [ABSTRACT FROM AUTHOR]

The chloroplast genomes of wild loquat can help to determine their place in the history of evolution. Here, we sequenced and assembled two novel wild loquat's chloroplast genomes, one is Eriobotrya elliptica, and the other is an unidentified wild loquat, which we named "YN-1". Their sizes are 159,471 bp and 159,399 bp, respectively. We also assembled a cultivated loquat named 'JFZ', its chloroplast genome size is 159,156 bp. A comparative study was conducted with six distinct species of loquats, including five wild loquats and one cultivated loquat. The results showed that both E. elliptica and "YN-1" have 127 genes, one gene more than E. fragrans, which is psbK. Regions trnF-GAA-ndhJ, petG-trnP-UGG, and rpl32-trnL-UAG were found to exhibit high variability. It was discovered that there was a positive selection on rpl22 and rps12. RNA editing analysis found several chilling stress-specific RNA editing sites, especially in rpl2 gene. Phylogenetic analysis results showed that "YN-1" is closely related to E. elliptica, E. obovata and E. henryi. [ABSTRACT FROM AUTHOR]

Plants, being sessile organisms, constantly need to respond to environmental stresses, often leading to the accumulation of reactive oxygen species (ROS). While ROS can be harmful, they also act as second messengers guiding plant growth and stress responses. Because chloroplasts are sensitive to environmental changes and are both a source and a target of ROS during stress conditions, they are important in conveying environmental changes to the nucleus, where acclimation responses are coordinated to maintain organellar and overall cellular homeostasis. ANAC102 has previously been established as a regulator of β-cyclocitral-mediated chloroplast-to-nucleus signaling, protecting plants against photooxidative stress. However, debates persist about where ANAC102 is located—in chloroplasts or in the nucleus. Our study, utilizing the genomic ANAC102 sequence driven by its native promoter, establishes ANAC102 primarily as a nuclear protein, lacking a complete N-terminal chloroplast-targeting peptide. Moreover, our research reveals the sensitivity of plants overexpressing ANAC102 to severe superoxide-induced chloroplast oxidative stress. Transcriptome analysis unraveled a dual role of ANAC102 in negatively and positively regulating genome-wide transcriptional responses to chloroplast oxidative stress. Through the integration of published data and our own study, we constructed a comprehensive transcriptional network, which suggests that ANAC102 exerts direct and indirect control over transcriptional responses through downstream transcription factor networks, providing deeper insights into the ANAC102-mediated regulatory landscape during oxidative stress. [ABSTRACT FROM AUTHOR]

The superoxide anion radical (O2·−) is a one-electron reduction product of molecular oxygen. Compared with other forms of reactive oxygen species (ROS), superoxide has limited reactivity. Nevertheless, superoxide reacts with nitric oxide, ascorbate, and the iron moieties of [Fe–S] cluster-containing proteins. Superoxide has largely been neglected as a signalling molecule in the plant literature in favour of the most stable ROS form, hydrogen peroxide. However, superoxide can accumulate in plant cells, particularly in meristems, where superoxide dismutase activity and ascorbate accumulation are limited (or absent), or when superoxide is generated within the lipid environment of membranes. Moreover, oxidation of the nucleus in response to environmental stresses is a widespread phenomenon. Superoxide is generated in many intracellular compartments including mitochondria, chloroplasts, and on the apoplastic/cell wall face of the plasma membrane. However, nuclear superoxide production and functions remain poorly documented in plants. Accumulating evidence suggests that the nuclear pools of antioxidants such as glutathione are discrete and separate from the cytosolic pools, allowing compartment-specific signalling in the nucleus. We consider the potential mechanisms of superoxide generation and targets in the nucleus, together with the importance of antioxidant processing in regulating superoxide signalling. [ABSTRACT FROM AUTHOR]

SUMMARY The intracellular localization of the florigen FLOWERING LOCUS T (FT) is important for its long‐distance transport toward the shoot apical meristem. However, the mechanisms regulating the FT localization remain poorly understood. Here, we discovered that in Arabidopsis thaliana, the chloroplast‐localized protein THYLAKOID FORMATION 1 (THF1) physically interacts with FT, sequestering FT in the outer chloroplast envelope. Loss of THF1 function led to temperature‐insensitive flowering, resulting in early flowering, especially under low ambient temperatures. THF1 mainly acts in the leaf vasculature and shoot apex to prevent flowering. Mutation of CONSTANS or FT completely suppressed the early flowering of thf1‐1 mutants. FT and THF1 interact via their anion binding pocket and coiled‐coil domain (CCD), respectively. Deletion of the CCD in THF1 by gene editing caused temperature‐insensitive early flowering similar to that observed in the thf1‐1 mutant. FT levels in the outer chloroplast envelope decreased in the thf1‐1 mutant, suggesting that THF1 is important for sequestering FT. Furthermore, THF1 protein levels decreased in seedlings grown at high ambient temperature, suggesting an explanation for its role in plant responses to ambient temperature. A thf1‐1 phosphatidylglycerolphosphate synthase 1 (pgp1) double mutant exhibited additive acceleration of flowering at 23 and 16°C, compared to the single mutants, indicating that THF1 and phosphatidylglycerol (PG) act as independent but synergistic regulators of temperature‐responsive flowering. Collectively, our results provide an understanding of the genetic pathway involving THF1 and its role in temperature‐responsive flowering and reveal a previously unappreciated additive interplay between THF1 and PG in temperature‐responsive flowering. [ABSTRACT FROM AUTHOR]

Diclofenac, often detected in environmental samples, poses a potential hazard to the aquatic environment. The present study aimed to understand the effect of this drug on photosynthetic apparatus, which is a little-known aspect of its phytotoxicity. Chloroplasts and thylakoids isolated from spinach (Spinacia oleracea) were used for this study and treated with various concentrations of diclofenac (from 125 to 4000 μM). The parameters of chlorophyll a fluorescence (the OJIP test) as measurements for both the intact chloroplasts and the thylakoid membranes revealed that isolated thylakoids showed greater sensitivity to the drug than chloroplasts. The relatively high concentration of diclofenac that is required to inhibit chloroplast and thylakoid functions suggests a narcotic effect of that drug on photosynthetic membranes, rather than a specific interaction with a particular element of the electron transport chain. Using confocal microscopy, we confirmed the degradation of the chloroplast structure after DCF treatment, which has not been previously reported in the literature. In conclusion, it can be assumed that diclofenac's action originated from a non-specific interaction with photosynthetic membranes, leading to the disruption in the function of the electron transport chain. This, in turn, decreases the efficiency of photosynthesis, transforming part of the PSII reaction centers into heat sinks and enhancing non-photochemical energy dissipation. [ABSTRACT FROM AUTHOR]

SUMMARY Biofortification of green leafy vegetables with pro‐vitamin A carotenoids, such as β‐carotene, has remained challenging to date. Here, we combined two strategies to achieve this goal. One of them involves producing β‐carotene in the cytosol of leaf cells to avoid the negative impacts on photosynthesis derived from changing the balance of carotenoids and chlorophylls in chloroplasts. The second approach involves the conversion of chloroplasts into non‐photosynthetic, carotenoid‐overaccumulating chromoplasts in leaves agroinfiltrated or infected with constructs encoding the bacterial phytoene synthase crtB, leaving other non‐engineered leaves of the plant to sustain normal growth. A combination of these two strategies, referred to as strategy C (for cytosolic production) and strategy P (for plastid conversion mediated by crtB), resulted in a 5‐fold increase in the amount of β‐carotene in Nicotiana benthamiana leaves. Following several attempts to further improve β‐carotene leaf contents by metabolic engineering, hormone treatments and genetic screenings, it was found that promoting the proliferation of plastoglobules with increased light‐intensity treatments not only improved β‐carotene accumulation but it also resulted in a much higher bioaccessibility. The combination of strategies C and P together with a more intense light treatment increased the levels of accessible β‐carotene 30‐fold compared to controls. We further demonstrated that stimulating plastoglobule proliferation with strategy P, but also with a higher‐light treatment alone, also improved β‐carotene contents and bioaccessibility in edible lettuce (Lactuca sativa) leaves. [ABSTRACT FROM AUTHOR]

Simple Summary: CRM domain proteins play key roles in plant growth and chloroplast development. To explore the role of CRM domain protein in the chloroplast development of rice, we cloned a rice CRM domain protein gene, YL4, and then conducted a tissue-specific expression analysis, subcellular localization, and transcription analysis. The experimental results showed that YL4 was highly expressed in leaves and localized to the chloroplast, and its mutation affected chloroplast-related gene transcription levels and some agronomic traits. These results indicate that the YL4 gene is a pivotal regulatory factor in chloroplast development and rice growth. Chloroplast RNA splicing and ribosome maturation (CRM) domain proteins are a family of plant-specific proteins associated with RNA binding. In this study, we have conducted a detailed characterization of a novel rice CRM gene (LOC_Os04g39060) mutant, yl4, which showed yellow-green leaves at all the stages, had fewer tillers, and had a decreased plant height. Map-based cloning and CRISPR/Cas9 editing techniques all showed that YL4 encoded a CRM domain protein in rice. In addition, subcellular localization revealed that YL4 was in chloroplasts. YL4 transcripts were highly expressed in all leaves and undetectable in roots and stems, and the mutation of YL4 affected the transcription of chloroplast-development-related genes. This study indicated that YL4 is essential for chloroplast development and affects some agronomic traits. [ABSTRACT FROM AUTHOR]

Summary: The coordinated interspecific variation in leaf traits and leaf lifespan is known as the leaf economic spectrum (LES). The limitation of CO2 diffusion to chloroplasts within the lamina is significant in C3 photosynthesis, resulting in a shortage of CO2 for Rubisco. Although Rubisco CO2/O2 specificity (SC/O) should be adaptively adjusted in response to the interspecific variation in CO2 concentrations [CO2] associated with Rubisco, SC/O variations across species along the LES remain unknown.We investigated the coordination among leaf traits, including SC/O, CO2 conductance, leaf protein content, and leaf mass area, across 23 woody C3 species coexisting on an oceanic island through phylogenetic correlation analyses.A high SC/O indicates a high CO2 specificity of Rubisco. SC/O was negatively correlated with [CO2] at Rubisco and total CO2 conductance within lamina, while it was positively correlated with leaf protein across species, regardless of phylogenetic constraint. A simulation analysis shows that the optimal SC/O for maximizing photosynthesis depends on both [CO2] at Rubisco sites and leaf protein per unit leaf area.SC/O is a key parameter along the LES axis and is crucial for maximizing photosynthesis across species and the adaptation of woody plants. [ABSTRACT FROM AUTHOR]

Chloroplasts accumulate in regions of plant cells exposed to irradiation to maximize light reception for efficient photosynthesis. This response is mediated by the blue‐light receptor phototropin. Upon the perception of blue light, phototropin is photoactivated, an unknown signal is transmitted from the photoactivated phototropin to distant chloroplasts, and the chloroplasts begin their directional movement. How activated phototropin initiates this signal transmission is unknown. Here, using the liverwort Marchantia polymorpha, we analysed whether increased photoactive phototropin levels mediate signal transmission and chloroplast behaviour during the accumulation response. The signal transmission rate was higher in transgenic cells overexpressing phototropin than in wild‐type cells. However, the chloroplast directional movement was similar between wild‐type and transgenic cells. Consistent with the observation, increasing the amount of photoactivated phototropin through higher blue‐light intensity also accelerated signal transmission but did not affect chloroplast behaviour in wild‐type cells. Photoactivation of phototropin under weak blue‐light led to the greater protein level of phosphorylated phototropin in cells overexpressing phototropin than in wild‐type cells, whereas the autophosphorylation level within each phototropin molecule was similar. These results indicate that the abundance of photoactivated phototropin modulates the signal transmission rate to distant chloroplasts but does not affect chloroplast behaviour during the accumulation response. Summary statement: Phototropin mediates the chloroplast accumulation response induced by blue light. This study shows that the abundance of photoactivated phototropin affects the signal transmission to distant chloroplasts, rather than their behaviour during the accumulation response in Marchantia polymorpha. [ABSTRACT FROM AUTHOR]

Photosynthesis is the foundation of life on Earth. However, if not well regulated, it can also generate excessive reactive oxygen species (ROS), which can cause photodamage. Regulation of photosynthesis is highly dynamic, responding to both environmental and metabolic cues, and occurs at many levels, from light capture to energy storage and metabolic processes. One general mechanism of regulation involves the reversible oxidation and reduction of protein thiol groups, which can affect the activity of enzymes and the stability of proteins. Such redox regulation has been well studied in stromal enzymes, but more recently, evidence has emerged of redox control of thylakoid lumenal enzymes. This review/hypothesis paper summarizes the latest research and discusses several open questions and challenges to achieving effective redox control in the lumen, focusing on the distinct environments and regulatory components of the thylakoid lumen, including the need to transport electrons across the thylakoid membrane, the effects of pH changes by the proton motive force (pmf) in the stromal and lumenal compartments, and the observed differences in redox states. These constraints suggest that activated oxygen species are likely to be major regulatory contributors to lumenal thiol redox regulation, with key components and processes yet to be discovered. [ABSTRACT FROM AUTHOR]

Arabidopsis thaliana possesses two different ion‐export mechanisms in the plastid inner envelope membrane. Due to a genome duplication, the transport proteins are encoded by partly redundant loci: K+‐efflux antiporter1 (KEA1) and KEA2 and mechanosensitive channel of small conductance‐like2 (MSL2) and MSL3. Thus far, a functional link between these two mechanisms has not been established. Here, we show that kea1msl2 loss‐of‐function mutants exhibit phenotypes such as slow growth, reduced photosynthesis and changes in chloroplast morphology, several of which are distinct from either single mutants and do not resemble kea1kea2 or msl2msl3 double mutants. Our data suggest that KEA1 and MSL2 function in concert to maintain plastid ion homeostasis and osmoregulation. Their interplay is critical for proper chloroplast development, organelle function, and plant performance. [ABSTRACT FROM AUTHOR]

The transcription of Arabidopsis organellar genes is performed by three nuclear-encoded RNA polymerases: RPOTm, RPOTmp, and RPOTp. The RPOTmp protein possesses ambiguous transit peptides, allowing participation in gene expression control in both mitochondria and chloroplasts, although its function in plastids is still under discussion. Here, we show that the overexpression of RPOTmp in Arabidopsis, targeted either to mitochondria or chloroplasts, disturbs the dormant seed state, and it causes the following effects: earlier germination, decreased ABA sensitivity, faster seedling growth, and earlier flowering. The germination of RPOTmp overexpressors is less sensitive to NaCl, while rpotmp knockout is highly vulnerable to salt stress. We found that mitochondrial dysfunction in the rpotmp mutant induces an unknown retrograde response pathway that bypasses AOX and ANAC017. Here, we show that RPOTmp transcribes the accD, clpP, and rpoB genes in plastids and up to 22 genes in mitochondria. [ABSTRACT FROM AUTHOR]

Thalictrum elegans Wall. ex Royle, a species within the family Ranunculaceae, is mainly distributed along forest margins and grassy slopes at altitudes 2700-4000 m on the Qinghai-Tibetan Plateau. Despite its wide distribution in alpine ecosystems, its genetic diversity remains poorly understood. In this study, we assembled and characterized the complete chloroplast genome of T. elegans, addressing a significant gap in our understanding of its genetic composition. The chloroplast genome is 155,864 base pairs long and contains 131 genes, including 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis of 15 representative Thalictrum species revealed that the genus can be classified into three clades. T. elegans along with another nine other species formed the largest monophyletic clade and is most closely related to T. petaloideum and T. foliosum. These findings enhance our understanding of the genetic diversity of T. elegans and contribute to its conservation and utilization. [ABSTRACT FROM AUTHOR]

To elucidate the genetic information and evolutionary relationships of Swertia, we initiated the sequencing of the complete chloroplast genome of Swertia davidii Franch. 1888, complemented by comparative analyses with closely related species. The chloroplast genome of S. davidii was 153,516 bp in length and exhibited a typical quadripartite structure. It contained two regions with Inverted Repeat lengths of 25,767 bp, located between one Large Single-Copy region (83,617 bp) and one Short Single-Copy region (18,365 bp). The chloroplast genome of S. davidii encoded 132 genes, including 87 protein-coding genes, 37 transfer RNA genes, and 8 ribosomal RNA genes. The overall GC content was 38.15%. Maximum likelihood phylogenetic analysis of Swertia based on 26 available plastomes showed a close relationship between S. davidii and S. kouitchensi. This study will contribute to the genetic preservation of the species and the phylogenetic study of Swertia. [ABSTRACT FROM AUTHOR]

SUMMARY BILE ACID: SODIUM SYMPORTER FAMILY PROTEIN 2 (BASS2) is localized within chloroplast membranes, facilitating the translocation of pyruvate and Na+ from the cytosol to the plastid, where pyruvate supports isopentenyl diphosphate (IPP) synthesis via the methylerythritol phosphate pathway in C3 plants. Nevertheless, the biological function of BASS2 in C4 plants has not been well defined. This study unveils a previously unidentified role of PvBASS2 in Na+ and pyruvate transport in seashore paspalum (Paspalum vaginatum), a halophytic C4 grass, indicating a specific cellular function within this plant species. Data showed that overexpression of PvBASS2 in seashore paspalum attenuated salt tolerance, whereas its RNAi lines exhibited enhanced salt resistance compared to wild‐type plants, suggesting a negative regulatory role of PvBASS2 in seashore paspalum salt tolerance. The constitutive overexpression of PvBASS2 was also found to reduce salt tolerance in Arabidopsis. Further study revealed that PvBASS2 negatively regulates seashore paspalum salt tolerance, possibly due to elevated Na+/K+ ratio, disrupted chloroplast structure, and reduced photosynthetic efficiency following exposure to salinity. Importantly, our subsequent investigations revealed that modulation of PvBASS2 expression in seashore paspalum influenced carbon dioxide assimilation, intermediary metabolites of the tricarboxylic acid cycle, and enzymatic activities under salinity treatment, which in turn led to alterations in free amino acid concentrations. Thus, this study reveals a role for BASS2 in the C4 plant seashore paspalum and enhances our comprehension of salt stress responses in C4 plants. [ABSTRACT FROM AUTHOR]

The plant endoplasmic reticulum (ER) contacts heterotypic membranes at membrane contact sites (MCSs) through largely undefined mechanisms. For instance, despite the well-established and essential role of the plant ER-chloroplast interactions for lipid biosynthesis, and the reported existence of physical contacts between these organelles, almost nothing is known about the ER-chloroplast MCS identity. Here we show that the Arabidopsis ER membrane-associated VAP27 proteins and the lipid-binding protein ORP2A define a functional complex at the ER-chloroplast MCSs. Specifically, through in vivo and in vitro association assays, we found that VAP27 proteins interact with the outer envelope membrane (OEM) of chloroplasts, where they bind to ORP2A. Through lipidomic analyses, we established that VAP27 proteins and ORP2A directly interact with the chloroplast OEM monogalactosyldiacylglycerol (MGDG), and we demonstrated that the loss of the VAP27-ORP2A complex is accompanied by subtle changes in the acyl composition of MGDG and PG. We also found that ORP2A interacts with phytosterols and established that the loss of the VAP27-ORP2A complex alters sterol levels in chloroplasts. We propose that, by interacting directly with OEM lipids, the VAP27-ORP2A complex defines plant-unique MCSs that bridge ER and chloroplasts and are involved in chloroplast lipid homeostasis. The plant endoplasmic reticulum (ER) interacts with other organelles at membrane contact sites. Here the authors show that plant-unique ER-chloroplasts contact sites marked by VAP27-1, VAP27-3, and ORP2a proteins function in chloroplast lipid homeostasis. [ABSTRACT FROM AUTHOR]

SUMMARY: The RNA regulatory network is a complex and dynamic regulation in plant cells involved in mRNA modification, translation, and degradation. Ras‐GAP SH3 domain‐binding protein (G3BP) is a scaffold protein for the assembly of stress granules (SGs) and is considered an antiviral component in mammals. However, the function of G3BP during virus infection in plants is still largely unknown. In this study, four members of the G3BP‐like proteins (NtG3BPLs) were identified in Nicotiana tabacum and the expression levels of NtG3BPL1 were upregulated during chilli veinal mottle virus (ChiVMV) infection. NtG3BPL1 was localized in the nucleus and cytoplasm, forming cytoplasmic granules under transient high‐temperature treatment, whereas the abundance of cytoplasmic granules was decreased under ChiVMV infection. Overexpression of NtG3BPL1 inhibited ChiVMV infection and delayed the onset of symptoms, whereas knockout of NtG3BPL1 promoted ChiVMV infection. In addition, NtG3BPL1 directly interacted with ChiVMV 6K2 protein, whereas 6K2 protein had no effect on NtG3BPL1‐derived cytoplasmic granules. Further studies revealed that the expression of NtG3BPL1 reduced the chloroplast localization of 6K2‐GFP and the NtG3BPL1‐6K2 interaction complex was localized in the cytoplasm. Furthermore, NtG3BPL1 promoted the degradation of 6K2 through autophagy pathway, and the accumulation of 6K2 and ChiVMV was affected by autophagy activation or inhibition in plants. Taken together, our results demonstrate that NtG3BPL1 plays a positive role in tobacco resistance against ChiVMV infection, revealing a novel mechanism of plant G3BP in antiviral strategy. Significance Statement: G3BP is a key component of cytoplasmic stress granules and exerts antiviral effects in mammals, but its function during plant virus infection remains unclear. Here, we revealed that NtG3BPL1 is induced upon ChiVMV infection and interacts with ChiVMV 6K2 to disturb the chloroplast localization of 6K2, and promote the degradation of 6K2, thereby limiting ChiVMV infection. This study enhances our understanding of the function of G3BP in plant virus infection. [ABSTRACT FROM AUTHOR]

Water hyacinth (Pontederia crassipes Mart.) is a monocotyledonous aquatic plant renowned for its rapid growth, extensive proliferation, biological invasiveness, and ecological resilience to variations in pH, nutrients, and temperature. The International Union for Conservation of Nature (IUCN) has listed P. crassipes among the top 100 invasive species. However, comprehensive genomic information, particularly concerning its mitochondrial genome (mitogenome), remains surprisingly limited. In this study, the complete mitogenome of P. crassipes was analyzed using bioinformatics approaches. The mitogenome is 399,263 bp long and contains 38 protein-coding genes (PCGs), 24 tRNA genes, and 3 rRNA genes. Sequence analysis revealed that the complete mitogenome of the species contains 3,289 dispersed repeats, and 765 RNA editing sites in protein-coding genes. The P. crassipes mitogenome possessed un-conserved structures, including extensive sequence transfer between its chloroplasts and mitochondria. Our study on the mitogenome of P. crassipes offers critical insights into its evolutionary patterns and phylogenetic relationships with related taxa. This research enhances our understanding of this invasive species, known for its significant biomass and rapid overgrowth in aquatic environments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: Woody plants display some photosynthetic activity in stems, but the biological role of stem photosynthesis and the specific contributions of bark and wood to carbon uptake and oxygen evolution remain poorly understood.We aimed to elucidate the functional characteristics of chloroplasts in stems of different ages in Fraxinus ornus. Our investigation employed diverse experimental approaches, including microsensor technology to assess oxygen production rates in whole stem, bark, and wood separately. Additionally, we utilized fluorescence lifetime imaging microscopy (FLIM) to characterize the relative abundance of photosystems I and II (PSI : PSII chlorophyll ratio) in bark and wood.Our findings revealed light‐induced increases in O2 production in whole stem, bark, and wood. We present the radial profile of O2 production in F. ornus stems, demonstrating the capability of stem chloroplasts to perform light‐dependent electron transport. Younger stems exhibited higher light‐induced O2 production and dark respiration rates than older ones.While bark emerged as the primary contributor to net O2 production under light conditions, our data underscored that wood chloroplasts are also photosynthetically active. The FLIM analysis unveiled a lower PSI abundance in wood than in bark, suggesting stem chloroplasts are not only active but also acclimate to the spectral composition of light reaching inner compartments. [ABSTRACT FROM AUTHOR]

Plant leaves contain multiple cell types which achieve distinct characteristics whilst still coordinating development within the leaf. The bundle sheath possesses larger individual cells and lower chloroplast content than the adjacent mesophyll, but how this morphology is achieved remains unknown. To identify regulatory mechanisms determining bundle sheath cell morphology we tested the effects of perturbing environmental (light) and endogenous signals (hormones) during leaf development of Oryza sativa (rice). Total chloroplast area in bundle sheath cells was found to increase with cell size as in the mesophyll but did not maintain a 'set‐point' relationship, with the longest bundle sheath cells demonstrating the lowest chloroplast content. Application of exogenous cytokinin and gibberellin significantly altered the relationship between cell size and chloroplast biosynthesis in the bundle sheath, increasing chloroplast content of the longest cells. Delayed exposure to light reduced the mean length of bundle sheath cells but increased corresponding leaf length, whereas premature light reduced final leaf length but did not affect bundle sheath cells. This suggests that the plant hormones cytokinin and gibberellin are regulators of the bundle sheath cell‐chloroplast relationship and that final bundle sheath length may potentially be affected by light‐mediated control of exit from the cell cycle. Summary statement: In rice (Oryza sativa) the timing of light exposure during leaf development changes mature bundle sheath morphology, reducing maximum cell length under extended darkness. Bundle sheath chloroplast biogenesis responds to changing cell size, with this relationship influenced by endogenous hormones. [ABSTRACT FROM AUTHOR]

Chloroplast function is essential for growth, development, and plant adaptation to stress. Organelle stress and plant defence responses were examined here using noxy8 (nonresponding to oxylipins 8) from a series of Arabidopsis mutants. The noxy8 mutation was located at the CLPC2 gene, encoding a chloroplast chaperone of the protease complex CLP. Although its CLPC1 paralogue is considered to generate redundancy, our data reveal significant differences distinguishing CLPC2 and CLPC1 functions. As such, clpc1 mutants displayed a major defect in housekeeping chloroplast proteostasis, leading to a pronounced reduction in growth and pigment levels, enhanced accumulation of chloroplast and cytosol chaperones, and resistance to fosmidomycin. Conversely, clpc2 mutants showed severe susceptibility to lincomycin inhibition of chloroplast translation and resistance to Antimycin A inhibition of mitochondrial respiration. In the response to Pseudomonas syringae pv. tomato, clpc2 but not clpc1 mutants were resistant to bacterial infection, showing higher salicylic acid levels, defence gene expression and 9‐LOX pathway activation. Our findings suggest CLPC2 and CLPC1 functional specificity, with a preferential involvement of CLPC1 in housekeeping processes and of CLPC2 in stress responses. Summary statement: The CLPC1 and CLPC2 chaperones participate in protein unfolding prior degradation by the chloroplast CLP protease. In contrast to previous data indicating functional redundancy, our results suggest CLPC2 and CLPC1 specificity, with a preferential involvement of CLPC1 in housekeeping processes and of CLPC2 in stress responses. [ABSTRACT FROM AUTHOR]

AbstractIn land plants, plastids acquired different functions and structures in parallel with the increasing genetic, developmental, and morphological diversity attained by the plant tissues. There are transition dynamics among the morpho-functional features of the different plastid types. This review is focused on plastid structure and interconversion with a focus on recent findings and a special attention to plastid types that are less known than chloroplasts. The morpho-physiological and biochemical differences, which explain the multiple functions of each plastid type and the transcriptional and post-translational modulation of plastid capabilities are here described. The structural dynamism of plastids is also discussed through their ability to produce protrusions called stromules and the activity of lipoprotein particles known as plastoglobules. As a consequence of the proteome differences among plastid types, the conversion from one type of plastid to another requires an organellar proteome reorganization with a turnover of plastid proteins, but also a differentially regulated import of nuclear-encoded proteins. Plastid degradation by macroautophagy and microautophagy pathways is also described. Taken together, all this information allows us to interpret plastids as sensors in development and plastid interconversion as a way that the plant uses to modify its growth. [ABSTRACT FROM AUTHOR]

Chloroplast-actin (cp-actin) filaments are crucial for light-induced chloroplast movement, and appear in the front region of moving chloroplasts when visualized using GFP-mouse Talin. They are short and thick, exist between a chloroplast and the plasma membrane, and move actively and rapidly compared to cytoplasmic long actin filaments that run through a cell. The average period during which a cp-actin filament was observed at the same position was less than 0.5 s. The average lengths of the cp-actin filaments calculated from those at the front region of the moving chloroplast and those around the chloroplast periphery after stopping the movement were almost the same, approximately 0.8 µm. Each cp-actin filament is shown as a dotted line consisting of 4–5 dots. The vector sum of cp-actin filaments in a moving chloroplast is parallel to the moving direction of the chloroplast, suggesting that the direction of chloroplast movement is regulated by the vector sum of cp-actin filaments. However, once the chloroplasts stopped moving, the vector sum of the cp-actin filaments around the chloroplast periphery was close to zero, indicating that the direction of movement was undecided. To determine the precise structure of cp-actin filaments under electron microscopy, Arabidopsis leaves and fern Adiantum capillus-veneris gametophytes were frozen using a high-pressure freezer, and observed under electron microscopy. However, no bundled microfilaments were found, suggesting that the cp-actin filaments were unstable even under high-pressure freezing. [ABSTRACT FROM AUTHOR]

SUMMARY: The lycophyte Phylloglossum drummondii is the sole inhabitant of its genus in the Huperzioideae group and one of a small minority of plants which perform uridine to cytidine RNA editing. We assembled the P. drummondii chloroplast and mitochondrial genomes and used RNA sequence data to build a comprehensive profile of organellar RNA editing events. In addition to many C‐to‐U editing events in both organelles, we found just four U‐to‐C editing events in the mitochondrial transcripts cob, nad1, nad5 and rpl2. These events are conserved in related lycophytes in the genera Huperzia and Phlegmariurus. De novo transcriptomes for three of these lycophytes were assembled to search for putative U‐to‐C RNA editing enzymes. Four putative U‐to‐C editing factors could be matched to the four mitochondrial U‐to‐C editing sites. Due to the unusually few numbers of U‐to‐C RNA editing sites, P. drummondii and related lycophytes are useful models for studying this poorly understood mechanism. [ABSTRACT FROM AUTHOR]

SUMMARY: The determination of physiological tolerance ranges of photosynthetic species and of the biochemical mechanisms underneath are fundamental to identify target processes and metabolites that will inspire enhanced plant management and production for the future. In this context, the terrestrial green algae within the genus Prasiola represent ideal models due to their success in harsh environments (polar tundras) and their extraordinary ecological plasticity. Here we focus on the outstanding Prasiola antarctica and compare two natural populations living in very contrasting microenvironments in Antarctica: the dry sandy substrate of a beach and the rocky bed of an ephemeral freshwater stream. Specifically, we assessed their photosynthetic performance at different temperatures, reporting for the first time gnsd values in algae and changes in thylakoid metabolites in response to extreme desiccation. Stream population showed lower α‐tocopherol content and thicker cell walls and thus, lower gnsd and photosynthesis. Both populations had high temperatures for optimal photosynthesis (around +20°C) and strong constitutive tolerance to freezing and desiccation. This tolerance seems to be related to the high constitutive levels of xanthophylls and of the cylindrical lipids di‐ and tri‐galactosyldiacylglycerol in thylakoids, very likely related to the effective protection and stability of membranes. Overall, P. antarctica shows a complex battery of constitutive and plastic protective mechanisms that enable it to thrive under harsh conditions and to acclimate to very contrasting microenvironments, respectively. Some of these anatomical and biochemical adaptations may partially limit photosynthesis, but this has a great potential to rise in a context of increasing temperature. Significance Statement: By using Prasiola antarctica as a model system, this work highlights the relevance of constitutive protection mechanisms involved on chloroplast functioning in harsh environments, especially the high proportion of cylindrical galactolipids and xanthophylls, and also reports the first measured gnsd ('gm') values in algae. This species shows a remarkable plasticity to ensure its success in contrasting terrestrial and fresh‐water microenvironments due to anatomical and biochemical changes, such as engrossed cell walls and accumulation of tocopherol. [ABSTRACT FROM AUTHOR]

Yellowing leaves are ideal materials for studying the metabolic pathways of photosynthetic pigment chloroplast development, and the mechanism of photosynthetic systems. Here, we obtained a triploid material HCC (2n = 3x = 26), which was derived from hybridization between the artificial tetraploid Cucumis × hytivus (2n = 4x = 38, HHCC) and the cultivated cucumber Cucumis sativus (2n = 2x = 14, CC), and this triploid HCC showed obvious leaf yellowing characteristics. Phenotypic observation results showed that chloroplast development was impaired, the chlorophyll content decreased, and photosynthesis decreased in yellowing HCC leaves. The transcriptome results indicated that HCC-GLK is significantly downregulated in HCC and participates in the regulation of leaf yellowing. GO enrichment analysis revealed that differential genes were enriched in the heme binding and tetrapyrrole binding pathways related to leaf color. KEGG enrichment analysis revealed that differential genes were predominantly enriched in photosynthesis-related pathways. The experimental results of VIGS and yeast hybridization showed that silencing the GLK gene can induce leaf yellowing in cucumber plants, and the GLK protein can affect plant chloroplast development by interacting with the CAB3C protein (light-harvesting chlorophyll a/b binding) in the plant chlorophyll synthesis pathway. The current findings have not only enhanced our understanding of the regulatory mechanism of the GLK transcription factor in cucumber but also introduced novel insights and directions for investigating the molecular mechanism underlying polyploid leaf yellowing. [ABSTRACT FROM AUTHOR]

Cyclamen persicum Mill., 1768, is a perennial herb of Primulaceae and is native to the Mediterranean region. In this study, we sequenced the chloroplast genome of Cyclamen persicum. Its complete chloroplast contained 151,911 nucleotides, including a large single-copy (LSC) region with a length of 83,191 bp, a small single-copy (SSC) region with a length of 17,922 bp, and a pair of reverse repeat IR regions (25,399 bp). The C. persicum chloroplast genome encoded 112 unique genes, including 78 protein-coding genes, 30 tRNA genes, and four rRNA genes. The GC content of the entire genome was 37.25%, lower than that of many angiosperm plastome. The phylogenetic result indicated that C. persicum exhibited the closest relationship with Cyclamen rohlfsianum, and provided new information for the phylogeny relationship of genus Cyclamen. [ABSTRACT FROM AUTHOR]

Polyspora axillaris (Roxb. ex Ker Gawl.) Sweet 1825, is a shrub or tree that is about 9 meters tall in the Theaceae family, mainly distributed in China and Vietnam, and it is widely used as a green tree species in many regions owing to its rapid growth and good adaptability. It is rich in various beneficial extracts for humans, but there are limited studies on it. In this study, we sequenced and annotated the complete plastome of P. axillaris. The chloroplast genome length of P. axillaris is 156,770 bp, with a total of 132 genes, including 37 tRNA genes, 8 rRNA genes and 87 protein-coding genes. The complete chloroplast genome of P. axillaris contains two Inverted Repeats (IRs) of 26,077 bp, a Large Single-Copy (LSC) region of 86,286 bp and a Small Single-Copy (SSC) region of 18,330 bp. The overall G/C content in the chloroplast is 37.3%. Phylogenetic inference shows that P. axillaris formed a sister relationship with P. hainanensis, along with 10 Theaceae species. The research result of P. axillaris will contribute to the genetic preservation of the species and the phylogenetic study of Polyspora. [ABSTRACT FROM AUTHOR]

Plant organelles predominantly rely on the actin cytoskeleton and the myosin motors for long-distance trafficking, while using microtubules and the kinesin motors mostly for short-range movement. The distribution and motility of organelles in the plant cell are fundamentally important to robust plant growth and defense. Chloroplasts, mitochondria, and peroxisomes are essential organelles in plants that function independently and coordinately during energy metabolism and other key metabolic processes. In response to developmental and environmental stimuli, these energy organelles modulate their metabolism, morphology, abundance, distribution and motility in the cell to meet the need of the plant. Consistent with their metabolic links in processes like photorespiration and fatty acid mobilization is the frequently observed inter-organellar physical interaction, sometimes through organelle membranous protrusions. The development of various organelle-specific fluorescent protein tags has allowed the simultaneous visualization of organelle movement in living plant cells by confocal microscopy. These energy organelles display an array of morphology and movement patterns and redistribute within the cell in response to changes such as varying light conditions, temperature fluctuations, ROS-inducible treatments, and during pollen tube development and immune response, independently or in association with one another. Although there are more reports on the mechanism of chloroplast movement than that of peroxisomes and mitochondria, our knowledge of how and why these three energy organelles move and distribute in the plant cell is still scarce at the functional and mechanistic level. It is critical to identify factors that control organelle motility coupled with plant growth, development, and stress response.

Chloroplast morphology changes during immunity, giving rise to tubule-like structures known as stromules. Stromules extend along microtubules and anchor to actin filaments along nuclei to promote perinuclear chloroplast clustering. This facilitates the transport of defense molecules/proteins from chloroplasts to the nucleus. Evidence for a direct role for stromules in immunity is lacking since, currently, there are no known genes that regulate stromule biogenesis. We show that a calponin homology (CH) domain containing kinesin, KIS1 (kinesin required for inducing stromules 1), is required for stromule formation during TNL [TIR (Toll/Interleukin-1 receptor)-type nucleotide-binding leucine-rich repeat]-immune receptor-mediated immunity. Furthermore, KIS1 is required for TNL-mediated immunity to bacterial and viral pathogens. The microtubule-binding motor domain of KIS1 is required for stromule formation while the actin-binding, CH domain is required for perinuclear chloroplast clustering. We show that KIS1 functions through early immune signaling components, EDS1 and PAD4, with salicylic acid-induced stromules requiring KIS1. Thus, KIS1 represents a player in stromule biogenesis.

Abstract 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.

Abstract In order to identify the key antioxidant defense systems used to cope with high-temperature stress in rice leaf chloroplasts following biochar supplementation, the present study compared the expression levels of chloroplast proteins related to antioxidant defense in high-temperature stressed rice leaves between without (C0) and with biochar supplementation (C40; 40 g biochar kg–1 soil). A total of sixteen differentially expressed antioxidant chloroplastic proteins were identified. Among them, three antioxidant enzyme proteins and eight thioredoxin proteins were 62–123% and 37–225% higher under the C40 treatment compared to C0, respectively. These results suggest that both antioxidant enzymes and the thioredoxin system are central to the biochar-mediated protection of rice leaves exposed to high-temperature stress.

Although the chloroplast genome (cpDNA) of higher plants is known to exist as a large protein-DNA complex called 'plastid nucleoid', researches on its DNA state and regulatory elements are limited. In this study, we performed the assay for transposase-accessible chromatin sequencing (ATAC-seq) on five common tissues across five grasses, and found that the accessibility of different regions in cpDNA varied widely, with the transcribed regions being highly accessible and accessibility patterns around gene start and end sites varying depending on the level of gene expression. Further analysis identified a total of 3970 putative protein binding footprints on cpDNAs of five grasses. These footprints were enriched in intergenic regions and co-localized with known functional elements. Footprints and their flanking accessibility varied dynamically among tissues. Cross-species analysis showed that footprints in coding regions tended to overlap non-degenerate sites and contain a high proportion of highly conserved sites, indicating that they are subject to evolutionary constraints. Taken together, our results suggest that the accessibility of cpDNA has biological implications and provide new insights into the transcriptional regulation of chloroplasts. ATAC-seq analyses across five grasses reveal that chloroplast DNA accessibility varies across regions and genes, and identified putative protein binding footprints that colocalize with known functional elements and are evolutionarily constrained [ABSTRACT FROM AUTHOR]

Chloroplasts are the powerhouse of the plant cell, and their activity must be matched to plant growth to avoid photooxidative damage. We have identified a posttranslational mechanism linking the eukaryotic target of rapamycin (TOR) kinase that promotes growth and the guanosine tetraphosphate (ppGpp) signaling pathway of prokaryotic origins that regulates chloroplast activity and photosynthesis in particular. We find that RelA SpoT homolog 3 (RSH3), a nuclear-encoded enzyme responsible for ppGpp biosynthesis, interacts directly with the TOR complex via a plant-specific amino-terminal region which is phosphorylated in a TOR-dependent manner. Down-regulating TOR activity causes a rapid increase in ppGpp synthesis in RSH3 overexpressors and reduces photosynthetic capacity in an RSH-dependent manner in wild-type plants. The TOR-RSH3 signaling axis therefore regulates the equilibrium between chloroplast activity and plant growth, setting a precedent for the regulation of organellar function by TOR. [ABSTRACT FROM AUTHOR]

In order to identify the key antioxidant defense systems used to cope with high-temperature stress in rice leaf chloroplasts following biochar supplementation, the present study compared the expression levels of chloroplast proteins related to antioxidant defense in high-temperature stressed rice leaves between without (C0) and with biochar supplementation (C40; 40 g biochar kg–1 soil). A total of sixteen differentially expressed antioxidant chloroplastic proteins were identified. Among them, three antioxidant enzyme proteins and eight thioredoxin proteins were 62–123% and 37–225% higher under the C40 treatment compared to C0, respectively. These results suggest that both antioxidant enzymes and the thioredoxin system are central to the biochar-mediated protection of rice leaves exposed to high-temperature stress. [ABSTRACT FROM AUTHOR]

The genus Abies is widely distributed across the world and is of high importance for forestry. Since chloroplasts are usually uniparentally inherited, they are an important tool for specific scientific issues like gene flow, parentage, migration and, in general, evolutionary analysis. Established genetic markers for organelles in conifers are rather limited to RFLP markers, which are more labour and time intensive, compared with SSR markers. Using QUIAGEN CLC Workbench 23.03, we aligned two chloroplast genomes from different Abies species (NCBI accessions: NC_039581, NC_042778, NC_039582, NC_042410, NC_035067, NC_062889, NC_042775, NC_057314, NC_041464, MH706706, MH047653 and MH510244) to identify potential SSR candidates. Further selection and development of forward and reverse primers was performed using the NCBI Primer Blast Server application. In this article, we introduce a remarkably polymorphic SSR marker set for various Abies species, which can be useful for other conifer genera, such as Cedrus, Pinus, Pseudotsuga or Picea. In total, 17 cpSSRs showed reliable amplification and polymorphisms in A. grandis with a total of 68 haplotypes detected. All 17 cpSSRs amplified in the tested Abies spp. In the other tested species, except for Taxus baccata, at least one primer was polymorphic. [ABSTRACT FROM AUTHOR]

Summary: RNA editing is a crucial modification in plants' organellar transcripts that converts cytidine to uridine (C‐to‐U; and sometimes uridine to cytidine) in RNA molecules. This post‐transcriptional process is controlled by the PLS‐class protein with a DYW domain, which belongs to the pentatricopeptide repeat (PPR) protein family. RNA editing is widespread in land plants; however, complex thalloid liverworts (Marchantiopsida) are the only group reported to lack both RNA editing and DYW‐PPR protein.The liverwort Cyathodium cavernarum (Marchantiopsida, Cyathodiaceae), typically found in cave habitats, was newly found to have 129 C‐to‐U RNA editing sites in its chloroplast and 172 sites in its mitochondria.The Cyathodium genus, specifically C. cavernarum, has a large number of PPR editing factor genes, including 251 DYW‐type PPR proteins. These DYW‐type PPR proteins may be responsible for C‐to‐U RNA editing in C. cavernarum.Cyathodium cavernarum possesses both PPR DYW proteins and RNA editing. Our analysis suggests that the remarkable RNA editing capability of C. cavernarum may have been acquired alongside the emergence of DYW‐type PPR editing factors. These findings provide insight into the evolutionary pattern of RNA editing in land plants. [ABSTRACT FROM AUTHOR]

Cover Legend Cells of the leaf of the liverwort Frullania fragilifolia (Frullaniaceae), showing cells of two types, including those with chloroplasts plus small oil bodies and those with chloroplasts plus a single large oil body, the latter termed 'ocelli'. Image courtesy of Des Callaghan (Slate et al., pp. 2411–2429).. [Extracted from the article]