ChloroP, a neural network-based method for predicting chloroplast transit peptides and their cleavage sites

The C4 photosynthesis bifunctional enzymes, PDRPs, of maize are co-opted to cytoplasmic viral replication complexes to promote infection of a prevalent potyvirus sugarcane mosaic virus

In maize, two pyruvate orthophosphate dikinase (PPDK) regulatory proteins, ZmPDRP1 and ZmPDRP2, are respectively specific to the chloroplast of mesophyll cells (MCs) and bundle sheath cells (BSCs). Functionally, ZmPDRP1/2 catalyse both phosphorylation/inactivation and dephosphorylation/activation of ZmPPDK, which is implicated as a major rate-limiting enzyme in C4 photosynthesis of maize. Our study here showed that maize plants lacking ZmPDRP1 or silencing of ZmPDRP1/2 confer resistance to a prevalent potyvirus sugarcane mosaic virus (SCMV). We verified that the C-terminal domain (CTD) of ZmPDRP1 plays a key role in promoting viral infection while independent of enzyme activity. Intriguingly, ZmPDRP1 and ZmPDRP2 re-localize to cytoplasmic viral replication complexes (VRCs) following SCMV infection. We identified that SCMV-encoded cytoplasmic inclusions protein CI targets directly ZmPDRP1 or ZmPDRP2 or their CTDs, leading to their re-localization to cytoplasmic VRCs. Moreover, we found that CI could be degraded by the 26S proteasome system, while ZmPDRP1 and ZmPDRP2 could up-regulate the accumulation level of CI through their CTDs by a yet unknown mechanism. Most importantly, with genetic, cell biological and biochemical approaches, we provide evidence that BSCs-specific ZmPDRP2 could accumulate in MCs of Zmpdrp1 knockout (KO) lines, revealing a unique regulatory mechanism crossing different cell types to maintain balanced ZmPPDK phosphorylation, thereby to keep maize normal growth. Together, our findings uncover the genetic link of the two cell-specific maize PDRPs, both of which are co-opted to VRCs to promote viral protein accumulation for robust virus infection.

Functional identification of specialized diterpene synthases from Chamaecyparis obtusa and C. obtusa var. formosana to illustrate the putative evolution of diterpene synthases in Cupressaceae

Chamaecyparis obtusa and C. obtusa var. formosana of the Cupressaceae family are well known for their fragrance and excellent physical properties. To investigate the biosynthesis of unique diterpenoid compounds, diterpene synthase genes for specialized metabolite synthesis were cloned from C. obtusa and C. obtusa var. formosana. Using an Escherichia coli co-expression system, eight diterpene synthases (diTPSs) were characterized. CoCPS and CovfCPS are class II monofunctional (+)-copalyl diphosphate synthases [(+)-CPSs]. Class I monofunctional CoLS and CovfLS convert (+)-copalyl diphosphate [(+)-CPP] to levopimaradiene, CoBRS, CovfBRS1, and CovfBRS3 convert (+)-CPP to (-)-beyerene, and CovfSDS converts (+)-CPP to (-)-sandaracopimaradiene. These enzymes are all monofunctional diterpene syntheses in Cupressaceae family of gymnosperm, and differ from those in Pinaceae. The discovery of the enzyme responsible for the biosynthesis of tetracyclic diterpene (-)-beyerene was characterized for the first time. Diterpene synthases with different catalytic functions exist in closely related species within the Cupressaceae family, indicating that this group of monofunctional diterpene synthases is particularly prone to the evolution of new functions and development of species-specific specialized diterpenoid constituents.

Chemical and transcriptomic analyses of leaf trichomes from Cistus creticus subsp. creticus reveal the biosynthetic pathways of certain labdane-type diterpenoids and their acetylated forms

Labdane-related diterpenoids (LRDs), a subgroup of terpenoids, exhibit structural diversity and significant commercial and pharmacological potential. LRDs share the characteristic decalin-labdanic core structure that derives from the cycloisomerization of geranylgeranyl diphosphate (GGPP). Labdanes derive their name from the oleoresin known as 'Labdanum', 'Ladano', or 'Aladano', used since ancient Greek times. Acetylated labdanes, rarely identified in plants, are associated with enhanced biological activities. Chemical analysis of Cistus creticus subsp. creticus revealed labda-7,13(E)-dien-15-yl acetate and labda-7,13(E)-dien-15-ol as major constituents. In addition, novel labdanes such as cis-abienol, neoabienol, ent-copalol, and one as yet unidentified labdane-type diterpenoid were detected for the first time. These compounds exhibit developmental regulation, with higher accumulation observed in young leaves. Using RNA-sequencing (RNA-seq) analysis of young leaf trichomes, it was possible to identify, clone, and eventually functionally characterize labdane-type diterpenoid synthase (diTPS) genes, encoding proteins responsible for the production of labda-7,13(E)-dien-15-yl diphosphate (endo-7,13-CPP), labda-7,13(E)-dien-15-yl acetate, and labda-13(E)-ene-8α-ol-15-yl acetate. Moreover, the reconstitution of labda-7,13(E)-dien-15-yl acetate and labda-13(E)-ene-8α-ol-15-yl acetate production in yeast is presented. Finally, the accumulation of LRDs in different plant tissues showed a correlation with the expression profiles of the corresponding genes.

Albino lethal 13, a chloroplast-imported protein required for chloroplast development in rice

Chloroplasts play a vital role in plant growth and development, which are the main sites of photosynthesis and the production of hormones and metabolites. Despite their significance, the regulatory mechanisms governing chloroplast development remain unclear. In our investigation, we identified a rice mutant with defective chloroplasts in rice (Oryza sativa L.), named albino lethal 13 (osal13), which displayed a distinct albino phenotype in leaves, ultimately resulting in seedling lethality. Molecular cloning revealed that OsAL13 encodes a novel rice protein with no homologous gene or known conserved domain. This gene was located in the chloroplast and exhibited constitutive expression in various tissues, particularly in green tissues and regions of active cell growth. Our study's findings reveal that RNAi-mediated knockdown of OsAL13 led to a pronounced albino phenotype, reduced chlorophyll and carotenoid contents, a vesicle chloroplast structure, and a decrease in the expression of chloroplast-associated genes. Consequently, the pollen fertility and seed setting rate were lower compared with the wild type. In contrast, the overexpression of OsAL13 resulted in an increased photosynthetic rate, a higher total grain number per panicle, and enhanced levels of indole-3-acetic acid (IAA) in the roots and gibberellin A3 (GA3) in the shoot. These outcomes provide new insights on the role of OsAL13 in regulating chloroplast development in rice.

Functional conservation of GENOMES UNCOUPLED1 in plastid-to-nucleus retrograde signaling in tomato

Retrograde signaling between plastids and the nucleus is vital for chloroplast biogenesis and environmental responses. GENOMES UNCOUPLED1 (GUN1) was proposed to be a central integrator of multiple retrograde signaling pathways in the model plant Arabidopsis thaliana (Arabidopsis). However, the function of GUN1 orthologs in other plant species has not been well studied. Here, we found that many GUN1 orthologs from the Solanaceae family have a short N-terminus before the first pentatricopeptide repeat (PPR) motif which is predicted as intrinsically disordered regions (IDRs). Functional analyses of tomato (Solanum lycopersicum L.) GUN1 (SlGUN1), which does not contain N-terminal IDRs, show that it can complement the GUN phenotype of the Arabidopsis gun1 mutant (Atgun1). However, in contrast to the AtGUN1 protein, which does contain the N-terminal IDRs, the SlGUN1 protein is highly accumulated even after chloroplast biogenesis is completed, suggesting that the N-terminal IDRs may determine the stability of the GUN1 protein. Furthermore, we generated tomato Slgun1 genome-edited mutants via the CRISPR-Cas9 system. The Slgun1 mutants exhibited a typical GUN phenotype under lincomycin (Lin) or norflurazon (NF) treatment. Moreover, Slgun1 mutants are hypersensitive to low concentrations of Lin or NF. Taken together, our results suggest that, although lacking the N-terminal IDRs, SlGUN1 plays conserved roles in plastid retrograde signaling in tomato plants.

Properties and Functional Analysis of Two Chorismate Mutases from Maritime Pine

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.

Rice LIKE EARLY STARVATION1 cooperates with FLOURY ENDOSPERM6 to modulate starch biosynthesis and endosperm development

In cereal grains, starch is synthesized by the concerted actions of multiple enzymes on the surface of starch granules within the amyloplast. However, little is known about how starch-synthesizing enzymes access starch granules, especially for amylopectin biosynthesis. Here, we show that the rice (Oryza sativa) floury endosperm9 (flo9) mutant is defective in amylopectin biosynthesis, leading to grains exhibiting a floury endosperm with a hollow core. Molecular cloning revealed that FLO9 encodes a plant-specific protein homologous to Arabidopsis (Arabidopsis thaliana) LIKE EARLY STARVATION1 (LESV). Unlike Arabidopsis LESV, which is involved in starch metabolism in leaves, OsLESV is required for starch granule initiation in the endosperm. OsLESV can directly bind to starch by its C-terminal tryptophan (Trp)-rich region. Cellular and biochemical evidence suggests that OsLESV interacts with the starch-binding protein FLO6, and loss-of-function mutations of either gene impair ISOAMYLASE1 (ISA1) targeting to starch granules. Genetically, OsLESV acts synergistically with FLO6 to regulate starch biosynthesis and endosperm development. Together, our results identify OsLESV-FLO6 as a non-enzymatic molecular module responsible for ISA1 localization on starch granules, and present a target gene for use in biotechnology to control starch content and composition in rice endosperm.

Capsicum chinense Jacq.-derived glutaredoxin (CcGRXS12) alters redox status of the cells to confer resistance against pepper mild mottle virus (PMMoV-I)

KEY MESSAGE

The CcGRXS12 gene protects plants from cellular oxidative damage that are caused by both biotic and abiotic stresses. The protein possesses GSH-disulphide oxidoreductase property but lacks Fe-S cluster assembly mechanism. Glutaredoxins (Grxs) are small, ubiquitous and multi-functional proteins. They are present in different compartments of plant cells. A chloroplast targeted Class I GRX (CcGRXS12) gene was isolated from Capsicum chinense during the pepper mild mottle virus (PMMoV) infection. Functional characterization of the gene was performed in Nicotiana benthamiana transgenic plants transformed with native C. chinense GRX (Nb:GRX), GRX-fused with GFP (Nb:GRX-GFP) and GRX-truncated for chloroplast sequences fused with GFP (Nb:Δ2MGRX-GFP). Overexpression of CcGRXS12 inhibited the PMMoV-I accumulation at the later stage of infection, accompanied with the activation of salicylic acid (SA) pathway pathogenesis-related (PR) transcripts and suppression of JA/ET pathway transcripts. Further, the reduced accumulation of auxin-induced Glutathione-S-Transferase (pCNT103) in CcGRXS12 overexpressing lines indicated that the protein could protect the plants from the oxidative stress caused by the virus. PMMoV-I infection increased the accumulation of pyridine nucleotides (PNs) mainly due to the reduced form of PNs (NAD(P)H), and it was high in Nb:GRX-GFP lines compared to other transgenic lines. Apart from biotic stress, CcGRXS12 protects the plants from abiotic stress conditions caused by H2O2 and herbicide paraquat. CcGRXS12 exhibited GSH-disulphide oxidoreductase activity in vitro; however, it was devoid of complementary Fe-S cluster assembly mechanism found in yeast. Overall, this study proves that CcGRXS12 plays a crucial role during biotic and abiotic stress in plants.

New plastids, old proteins: repeated endosymbiotic acquisitions in kareniacean dinoflagellates

Dinoflagellates are a diverse group of ecologically significant micro-eukaryotes that can serve as a model system for plastid symbiogenesis due to their susceptibility to plastid loss and replacement via serial endosymbiosis. Kareniaceae harbor fucoxanthin-pigmented plastids instead of the ancestral peridinin-pigmented ones and support them with a diverse range of nucleus-encoded plastid-targeted proteins originating from the haptophyte endosymbiont, dinoflagellate host, and/or lateral gene transfers (LGT). Here, we present predicted plastid proteomes from seven distantly related kareniaceans in three genera (Karenia, Karlodinium, and Takayama) and analyze their evolutionary patterns using automated tree building and sorting. We project a relatively limited ( ~ 10%) haptophyte signal pointing towards a shared origin in the family Chrysochromulinaceae. Our data establish significant variations in the functional distributions of these signals, emphasizing the importance of micro-evolutionary processes in shaping the chimeric proteomes. Analysis of plastid genome sequences recontextualizes these results by a striking finding the extant kareniacean plastids are in fact not all of the same origin, as two of the studied species (Karlodinium armiger, Takayama helix) possess plastids from different haptophyte orders than the rest.

Intrinsically Disordered Kiwellin Protein-Like Effectors Target Plant Chloroplasts and are Extensively Present in Rust Fungi

The effector proteins produced by plant pathogens are one of the essential components of host-pathogen interaction. Despite being important, most of the effector proteins remain unexplored due to the diversity in their primary sequence generated by the high selection pressure of the host immune system. However to maintain the primary function in the infection process, these effectors may tend to maintain their native protein fold to perform the corresponding biological function. In the present study, unannotated candidate secretory effector proteins of sixteen major plant fungal pathogens were analyzed to find the conserved known protein folds using homology, ab initio, and Alpha Fold/Rosetta Fold protein dimensional (3D) structure approaches. Several unannotated candidate effector proteins were found to match various known conserved protein families potentially involved in host defense manipulation in different plant pathogens. Surprisingly a large number of plant Kiwellin proteins fold like secretory proteins (> 100) were found in studied rust fungal pathogens. Many of them were predicted as potential effector proteins. Furthermore, template independent modelling using Alpha Fold/Rosetta Fold analysis and structural comparison of these candidates also predicted them to match with plant Kiwellin proteins. We also found plant Kiwellin matching proteins outside rusts including several non-pathogenic fungi suggesting the broad function of these proteins. One of the highest confidently modeled Kiwellin matching candidates effectors, Pstr_13960 (97.8%), from the Indian P. striiformis race Yr9 was characterized using overexpression, localization, and deletion studies in Nicotiana benthamiana. The Pstr_13960 suppressed the BAX-induced cell death and localized in the chloroplast. Furthermore, the expression of the Kiwellin matching region (Pst_13960_kiwi) alone suppressed the BAX-induced cell death in N. benthamiana despite the change of location to the cytoplasm and nucleus, suggesting the novel function of the Kiwellin core fold in rust fungi. Molecular docking showed that Pstr_13960 can interact with plant Chorismate mutases (CMs) using three loops conserved in plant and rust Kiwellins. Further analysis of Pstr_13960 showed to contain Intrinsically disordered regions (IDRs) in place of the N-terminal β1/β2 region found in plant Kiwellins suggesting the evolution of rust Kiwellins-like effectors (KLEs). Overall, this study reports the presence of a Kiwellin protein-like fold containing a novel effector protein family in rust fungi depicting a classical example of the evolution of effectors at the structure level as Kiwellin effectors show very low significant similarity to plant Kiwellin at the sequence level.

Characterization of chloroplast ribulose-5-phosphate-3-epimerase from the microalga Chlamydomonas reinhardtii

Carbon fixation relies on Rubisco and 10 additional enzymes in the Calvin-Benson-Bassham cycle. Epimerization of xylulose-5-phosphate (Xu5P) into ribulose-5-phosphate (Ru5P) contributes to the regeneration of ribulose-1,5-bisphosphate, the substrate of Rubisco. Ribulose-5-phosphate-3-epimerase (RPE, EC 5.1.3.1) catalyzes the formation of Ru5P, but it can also operate in the pentose-phosphate pathway by catalyzing the reverse reaction. Here, we describe the structural and biochemical properties of the recombinant RPE isoform 1 from Chlamydomonas (Chlamydomonas reinhardtii) (CrRPE1). The enzyme is a homo-hexamer that contains a zinc ion in the active site and exposes a catalytic pocket on the top of an α8β8 triose isomerase-type barrel as observed in structurally solved RPE isoforms from both plant and non-plant sources. By optimizing and developing enzyme assays to monitor the reversible epimerization of Ru5P to Xu5P and vice versa, we determined the catalytic parameters that differ from those of other plant paralogs. Despite being identified as a putative target of multiple thiol-based redox modifications, CrRPE1 activity is not affected by both reductive and oxidative treatments, indicating that enzyme catalysis is insensitive to possible redox alterations of cysteine residues. We mapped phosphorylation sites on the crystal structure, and the specific location at the entrance of the catalytic cleft supports a phosphorylation-based regulatory mechanism. This work provides an accurate description of the structural features of CrRPE1 and an in-depth examination of its catalytic and regulatory properties highlighting the physiological relevance of this enzyme in the context of photosynthetic carbon fixation.

Chloroplast phosphate transporter CrPHT4-7 regulates phosphate homeostasis and photosynthesis in Chlamydomonas

In eukaryotic cells, phosphorus is assimilated and utilized primarily as phosphate (Pi). Pi homeostasis is mediated by transporters that have not yet been adequately characterized in green algae. This study reports on PHOSPHATE TRANSPORTER 4-7 (CrPHT4-7) from Chlamydomonas reinhardtii, a member of the PHT4 transporter family, which exhibits remarkable similarity to AtPHT4;4 from Arabidopsis (Arabidopsis thaliana), a chloroplastic ascorbate transporter. Using fluorescent protein tagging, we show that CrPHT4-7 resides in the chloroplast envelope membrane. Crpht4-7 mutants, generated by the CRISPR/Cas12a-mediated single-strand templated repair, show retarded growth, especially in high light, reduced ATP level, strong ascorbate accumulation, and diminished non-photochemical quenching in high light. On the other hand, total cellular phosphorous content was unaffected, and the phenotype of the Crpht4-7 mutants could not be alleviated by ample Pi supply. CrPHT4-7-overexpressing lines exhibit enhanced biomass accumulation under high light conditions in comparison with the wild-type strain. Expressing CrPHT4-7 in a yeast (Saccharomyces cerevisiae) strain lacking Pi transporters substantially recovered its slow growth phenotype, demonstrating that CrPHT4-7 transports Pi. Even though CrPHT4-7 shows a high degree of similarity to AtPHT4;4, it does not display any substantial ascorbate transport activity in yeast or intact algal cells. Thus, the results demonstrate that CrPHT4-7 functions as a chloroplastic Pi transporter essential for maintaining Pi homeostasis and photosynthesis in C. reinhardtii.

Genomic imprints of unparalleled growth

Chlorella ohadii was isolated from desert biological soil crusts, one of the harshest habitats on Earth, and is emerging as an exciting new green model for studying growth, photosynthesis and metabolism under a wide range of conditions. Here, we compared the genome of C. ohadii, the fastest growing alga on record, to that of other green algae, to reveal the genomic imprints empowering its unparalleled growth rate and resistance to various stressors, including extreme illumination. This included the genome of its close relative, but slower growing and photodamage sensitive, C. sorokiniana UTEX 1663. A larger number of ribosome-encoding genes, high intron abundance, increased codon bias and unique genes potentially involved in metabolic flexibility and resistance to photodamage are all consistent with the faster growth of C. ohadii. Some of these characteristics highlight general trends in Chlorophyta and Chlorella spp. evolution, and others open new broad avenues for mechanistic exploration of their relationship with growth. This work entails a unique case study for the genomic adaptations and costs of exceptionally fast growth and sheds light on the genomic signatures of fast growth in photosynthetic cells. It also provides an important resource for future studies leveraging the unique properties of C. ohadii for photosynthesis and stress response research alongside their utilization for synthetic biology and biotechnology aims.

Diurnal Rhythms in the Red Seaweed Gracilariopsis chorda are Characterized by Unique Regulatory Networks of Carbon Metabolism

Cellular and physiological cycles are driven by endogenous pacemakers, the diurnal and circadian rhythms. Key functions such as cell cycle progression and cellular metabolism are under rhythmic regulation, thereby maintaining physiological homeostasis. The photoreceptors phytochrome and cryptochrome, in response to light cues, are central input pathways for physiological cycles in most photosynthetic organisms. However, among Archaeplastida, red algae are the only taxa that lack phytochromes. Current knowledge about oscillatory rhythms is primarily derived from model species such as Arabidopsis thaliana and Chlamydomonas reinhardtii in the Viridiplantae, whereas little is known about these processes in other clades of the Archaeplastida, such as the red algae (Rhodophyta). We used genome-wide expression profiling of the red seaweed Gracilariopsis chorda and identified 3,098 rhythmic genes. Here, we characterized possible cryptochrome-based regulation and photosynthetic/cytosolic carbon metabolism in this species. We found a large family of cryptochrome genes in G. chorda that display rhythmic expression over the diurnal cycle and may compensate for the lack of phytochromes in this species. The input pathway gates regulatory networks of carbon metabolism which results in a compact and efficient energy metabolism during daylight hours. The system in G. chorda is distinct from energy metabolism in most plants, which activates in the dark. The green lineage, in particular, land plants, balance water loss and CO2 capture in terrestrial environments. In contrast, red seaweeds maintain a reduced set of photoreceptors and a compact cytosolic carbon metabolism to thrive in the harsh abiotic conditions typical of intertidal zones.

More indications for redox-sensitive cysteine residues of the Arabidopsis 5-aminolevulinate dehydratase

Redox-dependent thiol-disulfide switches of cysteine residues are one of the significant posttranslational modifications of proteins to control rapidly their stability, activity, and protein interaction. Redox control also modulates the tetrapyrrole biosynthesis (TBS). Among the redox-dependent TBS enzymes, 5-aminolevulinic acid dehydratase (ALAD) was previously recognized to interact with reductants, such a thioredoxins or NADPH-dependent thioredoxin reductase C. In this report, we aim to verify the redox sensitivity of ALAD and identify the redox-reactive cysteine residues among the six cysteines of the mature protein form Arabidopsis. Based on structural modelling and comparative studies of wild-type ALAD and ALAD mutants with single and double Cys➔Ser substitutions under oxidizing and reducing conditions, we aim to predict the dimerization and oligomerisation of ALAD as well as the crucial Cys residues for disulfide bridge formation and enzyme activity. The Cys404Ser mutation led to a drastic inactivation of ALAD and redox-dependent properties of ALAD were severely impaired, when Cys71 was simultaneously mutated with Cys152 or Cys251. Cys71 is located in a flexible N-terminal arm of ALAD, which could allow intramolecular disulfide bridges with Cys residues at the surface of the remaining globule ALAD structure. As a result, we propose different roles of Cys residues for redox control, catalytic activity and Mg2+-dependent assembly.

An apicoplast-localized deubiquitinase contributes to the cell growth and apicoplast homeostasis of Toxoplasma gondii

Toxoplasma gondii is among the most important parasites worldwide. The apicoplast is a unique organelle shared by all Apicomplexan protozoa. Increasing lines of evidence suggest that the apicoplast possesses its own ubiquitination system. Deubiquitination is a crucial step executed by deubiquitinase (DUB) during protein ubiquitination. While multiple components of ubiquitination have been identified in T. gondii, the deubiquitinases involved remain unknown. The aim of the current study was to delineate the localization of TgOTU7 and elucidate its functions. TgOTU7 was specifically localized at the apicoplast, and its expression was largely regulated during the cell cycle. Additionally, TgOTU7 efficiently breaks down ubiquitin chains, exhibits linkage-nonspecific deubiquitinating activity and is critical for the lytic cycle and apicoplast biogenesis, similar to the transcription of the apicoplast genome and the nuclear genes encoding apicoplast-targeted proteins. Taken together, the results indicate that the newly described deubiquitinase TgOTU7 specifically localizes to the apicoplast and affects the cell growth and apicoplast homeostasis of T. gondii.

Natural variation in a short region of the Acidovorax citrulli type III-secreted effector AopW1 is associated with differences in cytotoxicity and host adaptation

Bacterial fruit blotch, caused by Acidovorax citrulli, is a serious disease of melon and watermelon. The strains of the pathogen belong to two major genetic groups: group I strains are strongly associated with melon, while group II strains are more aggressive on watermelon. A. citrulli secretes many protein effectors to the host cell via the type III secretion system. Here we characterized AopW1, an effector that shares similarity to the actin cytoskeleton-disrupting effector HopW1 of Pseudomonas syringae and with effectors from other plant-pathogenic bacterial species. AopW1 has a highly variable region (HVR) within amino acid positions 147 to 192, showing 14 amino acid differences between group I and II variants. We show that group I AopW1 is more toxic to yeast and Nicotiana benthamiana cells than group II AopW1, having stronger actin filament disruption activity, and increased ability to induce cell death and reduce callose deposition. We further demonstrated the importance of some amino acid positions within the HVR for AopW1 cytotoxicity. Cellular analyses revealed that AopW1 also localizes to the endoplasmic reticulum, chloroplasts, and plant endosomes. We also show that overexpression of the endosome-associated protein EHD1 attenuates AopW1-induced cell death and increases defense responses. Finally, we show that sequence variation in AopW1 plays a significant role in the adaptation of group I and II strains to their preferred hosts, melon and watermelon, respectively. This study provides new insights into the HopW1 family of bacterial effectors and provides first evidence on the involvement of EHD1 in response to biotic stress.

Discovery and Mode-of-Action Characterization of a New Class of Acetolactate Synthase-Inhibiting Herbicides

Herbicides are effective tools to manage weeds and enable food production and sustainable agriculture. Corteva Agriscience R&D has recently discovered new diphenyl-ether compounds displaying excellent postemergent efficacy on important weed species along with corn safety. Here, we describe the chemistry, biology, biochemistry, and computational modeling research that led to the discovery and elucidation of the primary mode of action for these compounds. The target protein was found to be acetolactate synthase (ALS), a key enzyme in the biosynthesis of branched chain amino acids (valine, leucine, and isoleucine). While weed resistance evolution to ALS herbicides is widespread, the molecular interaction of the diphenyl-ether compounds at the active site of the ALS enzyme differs significantly from that of some commercial ALS inhibitors. The unique biochemical profile of these molecules along with their excellent herbicidal activity and corn selectivity make them a noteworthy development in the pursuit of novel, safe, and sustainable weed control solutions.

A Novel Isoprene Synthase from the Monocot Tree Copernicia prunifera (Arecaceae) Confers Enhanced Drought Tolerance in Transgenic Arabidopsis

The capacity to emit isoprene, among other stresses, protects plants from drought, but the molecular mechanisms underlying this trait are only partly understood. The Arecaceae (palms) constitute a very interesting model system to test the involvement of isoprene in enhancing drought tolerance, as their high isoprene emissions may have contributed to make them hyperdominant in neotropical dry forests, characterized by recurrent and extended periods of drought stress. In this study we isolated and functionally characterized a novel isoprene synthase, the gene responsible for isoprene biosynthesis, from Copernicia prunifera, a palm from seasonally dry tropical forests. When overexpressed in the non-emitter Arabidopsis thaliana, CprISPS conferred significant levels of isoprene emission, together with enhanced tolerance to water limitation throughout plant growth and development, from germination to maturity. CprISPS overexpressors displayed higher germination, cotyledon/leaf greening, water usage efficiency, and survival than WT Arabidopsis under various types of water limitation. This increased drought tolerance was accompanied by a marked transcriptional up-regulation of both ABA-dependent and ABA-independent key drought response genes. Taken together, these results demonstrate the capacity of CprISPS to enhance drought tolerance in Arabidopsis and suggest that isoprene emission could have evolved in Arecaceae as an adaptive mechanism against drought.

The first multi-tissue genome-scale metabolic model of a woody plant highlights suberin biosynthesis pathways in Quercus suber

Over the last decade, genome-scale metabolic models have been increasingly used to study plant metabolic behaviour at the tissue and multi-tissue level under different environmental conditions. Quercus suber, also known as the cork oak tree, is one of the most important forest communities of the Mediterranean/Iberian region. In this work, we present the genome-scale metabolic model of the Q. suber (iEC7871). The metabolic model comprises 7871 genes, 6231 reactions, and 6481 metabolites across eight compartments. Transcriptomics data was integrated into the model to obtain tissue-specific models for the leaf, inner bark, and phellogen, with specific biomass compositions. The tissue-specific models were merged into a diel multi-tissue metabolic model to predict interactions among the three tissues at the light and dark phases. The metabolic models were also used to analyse the pathways associated with the synthesis of suberin monomers, namely the acyl-lipids, phenylpropanoids, isoprenoids, and flavonoids production. The models developed in this work provide a systematic overview of the metabolism of Q. suber, including its secondary metabolism pathways and cork formation.

The tomato chloroplast stromal proteome compendium elucidated by leveraging a plastid protein-localization prediction Atlas

Tomato (Solanum lycopersicum) is a model species for studying fruit development, wounding, herbivory, and pathogen attack. Despite tomato's world-wide economic importance and the role of chloroplasts as metabolic hubs and integrators of environmental cues, little is known about the stromal proteome of tomato. Using a high-yielding protocol for chloroplast and stromal protein isolation, MudPIT nano-LC-MS/MS analyses, a robust in-house protein database (the Atlas) for predicting the plastid localization of tomato proteins, and rigorous selection criteria for inclusion/exclusion in the stromal proteome, we identified 1,278 proteins of the tomato stromal proteome. We provide one of the most robust stromal proteomes available to date with empirical evidence for 545 and 92 proteins not previously described for tomato plastids and the Arabidopsis stroma, respectively. The relative abundance of tomato stromal proteins was determined using the exponentially modified protein abundance index (emPAI). Comparison of the abundance of tomato and Arabidopsis stromal proteomes provided evidence for the species-specific nature of stromal protein homeostasis. The manual curation of the tomato stromal proteome classified proteins into ten functional categories resulting in an accessible compendium of tomato chloroplast proteins. After curation, only 91 proteins remained as unknown, uncharacterized or as enzymes with unknown functions. The curation of the tomato stromal proteins also indicated that tomato has a number of paralogous proteins, not present in Arabidopsis, which accumulated to different levels in chloroplasts. As some of these proteins function in key metabolic pathways or in perceiving or transmitting signals critical for plant adaptation to biotic and abiotic stress, these data suggest that tomato may modulate the bidirectional communication between chloroplasts and nuclei in a novel manner. The stromal proteome provides a fertile ground for future mechanistic studies in the field of tomato chloroplast-nuclear signaling and are foundational for our goal of elucidating the dynamics of the stromal proteome controlled by the solanaceous-specific, stromal, and wound-inducible leucine aminopeptidase A of tomato.

A chloroplast protein atlas reveals punctate 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 1,034 candidate chloroplast proteins using fluorescent protein tagging in the model alga Chlamydomonas reinhardtii. The localizations provide insights into the functions of poorly characterized proteins; identify novel components of nucleoids, plastoglobules, and the pyrenoid; and reveal widespread protein targeting to multiple compartments. We discovered and further characterized cellular organizational features, including eleven chloroplast punctate structures, cytosolic crescent structures, and unexpected spatial distributions of enzymes within the chloroplast. We also used machine learning to predict the localizations of other nuclear-encoded Chlamydomonas proteins. The strains and localization atlas developed here will serve as a resource to accelerate studies of chloroplast architecture and functions.

Characterization of Chlamydomonas voltage-gated calcium channel and its interaction with photoreceptor support VGCC modulated photobehavioral response in the green alga

Calcium (Ca2+) signaling plays a major role in regulating multiple processes in living cells. The photoreceptor potential in Chlamydomonas triggers the generation of all or no flagellar Ca2+ currents that cause membrane depolarization across the eyespot and flagella. Modulation in membrane potential causes changes in the flagellar waveform, and hence, alters the beating patterns of Chlamydomonas flagella. The rhodopsin-mediated eyespot membrane potential is generated by the photoreceptor Ca2+ current or P-current however, the flagellar Ca2+ currents are mediated by unidentified voltage-gated calcium (VGCC or CaV) and potassium channels (VGKC). The voltage-gated ion channel that associates with ChRs to generate Ca2+ influx across the flagella and its cellular distribution has not yet been identified. Here, we identified putative VGCCs from algae and predicted their novel properties through insilico analysis. We further present experimental evidence on Chlamydomonas reinhardtii VGCCs to predict their novel physiological roles. Our experimental evidences showed that CrVGCC4 localizes to the eyespot and flagella of Chlamydomonas and associates with channelrhodopsins (ChRs). Further in silico interactome analysis of CrVGCCs suggested that they putatively interact with photoreceptor proteins, calcium signaling, and intraflagellar transport components. Expression analysis indicated that these VGCCs and their putative interactors can be perturbed by light stimuli. Collectively, our data suggest that VGCCs in general, and VGCC4 in particular, might be involved in the regulation of the photobehavioral response of Chlamydomonas.

BE3 is the major branching enzyme isoform required for amylopectin synthesis in Chlamydomonas reinhardtii

Starch-branching enzymes (BEs) are essential for starch synthesis in both plants and algae where they influence the architecture and physical properties of starch granules. Within Embryophytes, BEs are classified as type 1 and type 2 depending on their substrate preference. In this article, we report the characterization of the three BE isoforms encoded in the genome of the starch producing green algae Chlamydomonas reinhardtii: two type 2 BEs (BE2 and BE3) and a single type 1 BE (BE1). Using single mutant strains, we analyzed the consequences of the lack of each isoform on both transitory and storage starches. The transferred glucan substrate and the chain length specificities of each isoform were also determined. We show that only BE2 and BE3 isoforms are involved in starch synthesis and that, although both isoforms possess similar enzymatic properties, BE3 is critical for both transitory and storage starch metabolism. Finally, we propose putative explanations for the strong phenotype differences evidenced between the C. reinhardtii be2 and be3 mutants, including functional redundancy, enzymatic regulation or alterations in the composition of multimeric enzyme complexes.

The hops (Humulus lupulus) genome contains a mid-sized terpene synthase family that shows wide functional and allelic diversity

BACKGROUND

Hops (Humulus lupulus L.) are a dioecious climbing perennial, with the dried mature "cones" (strobili) of the pistillate/female inflorescences being widely used as both a bittering agent and to enhance the flavour of beer. The glandular trichomes of the bract and bracteole flowering structures of the cones produce an abundance of secondary metabolites, such as terpenoids, bitter acids and prenylated phenolics depending on plant genetics, developmental stage and environment. More knowledge is required on the functional and allelic diversity of terpene synthase (TPS) genes responsible for the biosynthesis of volatile terpenes to assist in flavour-directed hop breeding.

RESULTS

Major volatile terpene compounds were identified using gas chromatography-mass spectrometry (GC-MS) in the ripe cones of twenty-one hop cultivars grown in New Zealand. All cultivars produced the monoterpene β-myrcene and the sesquiterpenes α-humulene and β-caryophyllene, but the quantities varied broadly. Other terpenes were found in large quantities in only a smaller subset of cultivars, e.g. β-farnesene (in seven cultivars) and α-pinene (in four). In four contrasting cultivars (Wakatu™, Wai-iti™, Nelson Sauvin™, and 'Nugget'), terpene production during cone development was investigated in detail, with concentrations of some of the major terpenes increasing up to 1000-fold during development and reaching maximal levels from 50-60 days after flowering. Utilising the published H. lupulus genome, 87 putative full-length and partial terpene synthase genes were identified. Alleles corresponding to seven TPS genes were amplified from ripe cone cDNA from multiple cultivars and subsequently functionally characterised by transient expression in planta. Alleles of the previously characterised HlSTS1 produced humulene/caryophyllene as the major terpenes. HlRLS alleles produced (R)-(-)-linalool, whilst alleles of two sesquiterpene synthase genes, HlAFS1 and HlAFS2 produced α-farnesene. Alleles of HlMTS1, HlMTS2 and HlTPS1 were inactive in all the hop cultivars studied.

CONCLUSIONS

Alleles of four TPS genes were identified and shown to produce key aroma volatiles in ripe hop cones. Multiple expressed but inactive TPS alleles were also identified, suggesting that extensive loss-of-function has occurred during domestication and breeding of hops. Our results can be used to develop hop cultivars with novel/improved terpene profiles using marker-assisted breeding strategies to select for, or against, specific TPS alleles.

Chloroplast translation factor EF-Tu of Arabidopsis thaliana can be inactivated via oxidation of a specific cysteine residue

Translational elongation factor EF-Tu, which delivers aminoacyl-tRNA to the ribosome, is susceptible to inactivation by reactive oxygen species (ROS) in the cyanobacterium Synechocystis sp. PCC 6803. However, the sensitivity to ROS of chloroplast-localized EF-Tu (cpEF-Tu) of plants remains to be elucidated. In the present study, we generated a recombinant cpEF-Tu protein of Arabidopsis thaliana and examined its sensitivity to ROS in vitro. In cpEF-Tu that lacked a bound nucleotide, one of the two cysteine residues, Cys149 and Cys451, in the mature protein was sensitive to oxidation by H2O2, with the resultant formation of sulfenic acid. The translational activity of cpEF-Tu, as determined with an in vitro translation system, derived from Escherichia coli, that had been reconstituted without EF-Tu, decreased with the oxidation of a cysteine residue. Replacement of Cys149 with an alanine residue rendered cpEF-Tu insensitive to inactivation by H2O2, indicating that Cys149 might be the target of oxidation. In contrast, cpEF-Tu that had bound either GDP or GTP was less sensitive to oxidation by H2O2 than nucleotide-free cpEF-Tu. The addition of thioredoxin f1, a major thioredoxin in the Arabidopsis chloroplast, to oxidized cpEF-Tu allowed the reduction of Cys149 and the reactivation of cpEF-Tu, suggesting that the oxidation of cpEF-Tu might be a reversible regulatory mechanism that suppresses the chloroplast translation system in a redox-dependent manner.

Expression of symptoms elicited by a hammerhead viroid through RNA silencing is related to population bottlenecks in the infected host

Chlorosis is frequently incited by viroids, small nonprotein-coding, circular RNAs replicating in nuclei (family Pospiviroidae) or chloroplasts (family Avsunviroidae). Here, we investigated how chrysanthemum chlorotic mottle viroid (CChMVd, Avsunviroidae) colonizes, evolves and initiates disease. Progeny variants of natural and mutated CChMVd sequence variants inoculated in chrysanthemum plants were characterized, and plant responses were assessed by molecular assays. We showed that: chlorotic mottle induced by CChMVd reflects the spatial distribution and evolutionary behaviour in the infected host of pathogenic (containing a UUUC tetranucleotide) and nonpathogenic (lacking such a pathogenic determinant) variants; and RNA silencing is involved in the initiation of the chlorosis in symptomatic leaf sectors through a viroid-derived small RNA containing the pathogenic determinant that directs AGO1-mediated cleavage of the mRNA encoding the chloroplastic transketolase. This study provides the first evidence that colonization of leaf tissues by CChMVd is characterized by segregating variant populations differing in pathogenicity and with the ability to colonize leaf sectors (bottlenecks) and exclude other variants (superinfection exclusion). Importantly, no specific pathogenic viroid variants were found in the chlorotic spots caused by chrysanthemum stunt viroid (Pospiviroidae), thus establishing a clear distinction on how members of the two viroid families trigger chlorosis in the same host.

An ancient metalloenzyme evolves through metal preference modulation

Evolution creates functional diversity of proteins, the essential building blocks of all biological systems. However, studies of natural proteins sampled across the tree of life and evaluated in a single experimental system are lacking. Almost half of enzymes require metals, and metalloproteins tend to optimally utilize the physicochemical properties of a specific metal co-factor. Life must adapt to changes in metal bioavailability, including those during the transition from anoxic to oxic Earth or pathogens' exposure to nutritional immunity. These changes can challenge the ability of metalloenzymes to maintain activity, presumptively driving their evolution. Here we studied metal-preference evolution within the natural diversity of the iron/manganese superoxide dismutase (SodFM) family of reactive oxygen species scavengers. We identified and experimentally verified residues with conserved roles in determining metal preference that, when combined with an understanding of the protein's evolutionary history, improved prediction of metal utilization across the five SodFM subfamilies defined herein. By combining phylogenetics, biochemistry and structural biology, we demonstrate that SodFM metal utilization can be evolutionarily fine tuned by sliding along a scale between perfect manganese and iron specificities. Over the history of life, SodFM metal preference has been modulated multiple independent times within different evolutionary and ecological contexts, and can be changed within short evolutionary timeframes.

Biosynthesis of monoterpenoid and sesquiterpenoid as natural flavors and fragrances

Terpenoids are a large class of plant-derived compounds, that constitute the main components of essential oils and are widely used as natural flavors and fragrances. The biosynthesis approach presents a promising alternative route in terpenoid production compared to plant extraction or chemical synthesis. In the past decade, the production of terpenoids using biotechnology has attracted broad attention from both academia and the industry. With the growing market of flavor and fragrance, the production of terpenoids directed by synthetic biology shows great potential in promoting future market prospects. Here, we reviewed the latest advances in terpenoid biosynthesis. The engineering strategies for biosynthetic terpenoids were systematically summarized from the enzyme, metabolic, and cellular dimensions. Additionally, we analyzed the key challenges from laboratory production to scalable production, such as key enzyme improvement, terpenoid toxicity, and volatility loss. To provide comprehensive technical guidance, we collected milestone examples of biosynthetic mono- and sesquiterpenoids, compared the current application status of chemical synthesis and biosynthesis in terpenoid production, and discussed the cost drivers based on the data of techno-economic assessment. It is expected to provide critical insights into developing translational research of terpenoid biomanufacturing.

Sequence Characteristics and Expression Analysis of the Gene Encoding Sedoheptulose-1,7-Bisphosphatase, an Important Calvin Cycle Enzyme in Upland Cotton (Gossypium hirsutum L.)

Sedoheptulose-1,7-bisphosphatase (SBPase, EC 3.1.3.37) is a key enzyme in the plant Calvin cycle and one of the main rate-limiting enzymes in the plant photosynthesis pathway. Many studies have demonstrated that the SBPase gene plays an important role in plant photosynthetic efficiency, yield, and stress responses; however, few studies have been conducted on the function and expression of the GhSBPase gene in upland cotton. In this study, our results showed that the coding sequence (CDS) of GhSBPase gene was 1182 bp, encoding a protein with 393 amino acids. The GhSBPase protein had adenosine monophosphate (AMP) binding site and a FIG (FBPase/IMPase/glpX) domain, and had six Cys residues and a CGGT(A/Q)C motif that were involved in redox regulation in plants. Evolutionarily, the GhSBPase protein clustered into the dicotyledon subgroup and was most closely related to the tomato SlSBPase protein. Western-blot analysis further indicated that the GhSBPase gene was indeed the gene encoding the SBPase protein in upland cotton. The GhSBPase protein was localized in chloroplast, which was consistent with its function as a key enzyme in photosynthesis. The GhSBPase gene was specifically highly expressed in leaves, and its expression level was significantly lower in a yellow-green leaf mutant than in the wild type. Moreover, the GhSBPase expression was in response to drought, salt, high- and low-temperature stress, and exhibits different expression patterns. The GhSBPase promoter had the cis-acting elements in response to abiotic stress, phytohormone, and light. In addition, the GhSBPase expression was positively correlated with the chlorophyll fluorescence parameters, suggesting that changes in the expression of the GhSBPase had potential applicability in breeding for enhanced cotton photosynthetic efficiency. These results will help to understand the function of the GhSBPase gene in photosynthesis and the adaptability of plants to external stress and provide important gene information for the high-yield breeding of crops in the future.

The Chlamydomonas reinhardtii chloroplast envelope protein LCIA transports bicarbonate in planta

LCIA is a chloroplast envelope protein associated with the CO2 concentrating mechanism of the green alga Chlamydomonas reinhardtii. LCIA is postulated to be a HCO3- channel, but previous studies were unable to show that LCIA was actively transporting bicarbonate in planta. Therefore, LCIA activity was investigated more directly in two heterologous systems: an E. coli mutant (DCAKO) lacking both native carbonic anhydrases and an Arabidopsis mutant (βca5) missing the plastid carbonic anhydrase βCA5. Both DCAKO and βca5 cannot grow in ambient CO2 conditions, as they lack carbonic anhydrase-catalyzed production of the necessary HCO3- concentration for lipid and nucleic acid biosynthesis. Expression of LCIA restored growth in both systems in ambient CO2 conditions, which strongly suggests that LCIA is facilitating HCO3- uptake in each system. To our knowledge, this is the first direct evidence that LCIA moves HCO3- across membranes in bacteria and plants. Furthermore, the βca5 plant bioassay used in this study is the first system for testing HCO3- transport activity in planta, an experimental breakthrough that will be valuable for future studies aimed at improving the photosynthetic efficiency of crop plants using components from algal CO2 concentrating mechanisms.

Algal rhodopsins encoding diverse signal sequence holds potential for expansion of organelle optogenetics

Rhodopsins have been extensively employed for optogenetic regulation of bioelectrical activity of excitable cells and other cellular processes across biological systems. Various strategies have been adopted to attune the cellular processes at the desired subcellular compartment (plasma membrane, endoplasmic reticulum, Golgi, mitochondria, lysosome) within the cell. These strategies include-adding signal sequences, tethering peptides, specific interaction sites, or mRNA elements at different sites in the optogenetic proteins for plasma membrane integration and subcellular targeting. However, a single approach for organelle optogenetics was not suitable for the relevant optogenetic proteins and often led to the poor expression, mislocalization, or altered physical and functional properties. Therefore, the current study is focused on the native subcellular targeting machinery of algal rhodopsins. The N- and C-terminus signal prediction led to the identification of rhodopsins with diverse organelle targeting signal sequences for the nucleus, mitochondria, lysosome, endosome, vacuole, and cilia. Several identified channelrhodopsins and ion-pumping rhodopsins possess effector domains associated with DNA metabolism (repair, replication, and recombination) and gene regulation. The identified algal rhodopsins with diverse effector domains and encoded native subcellular targeting sequences hold immense potential to establish expanded organelle optogenetic regulation and associated cellular signaling.

Genome-wide identification and comparative analyses of key genes involved in C4 photosynthesis in five main gramineous crops

Compared to C₃ species, C₄ plants showed higher photosynthetic capacity as well as water and nitrogen use efficiency due to the presence of the C₄ photosynthetic pathway. Previous studies have shown that all genes required for the C₄ photosynthetic pathway exist in the genomes of C₃ species and are expressed. In this study, the genes encoding six key C₄ photosynthetic pathway enzymes (β-CA, PEPC, ME, MDH, RbcS, and PPDK) in the genomes of five important gramineous crops (C₄: maize, foxtail millet, and sorghum; C₃: rice and wheat) were systematically identified and compared. Based on sequence characteristics and evolutionary relationships, their C₄ functional gene copies were distinguished from non-photosynthetic functional gene copies. Furthermore, multiple sequence alignment revealed important sites affecting the activities of PEPC and RbcS between the C₃ and C₄ species. Comparisons of expression characteristics confirmed that the expression patterns of non-photosynthetic gene copies were relatively conserved among species, while C₄ gene copies in C₄ species acquired new tissue expression patterns during evolution. Additionally, multiple sequence features that may affect C₄ gene expression and subcellular localization were found in the coding and promoter regions. Our work emphasized the diversity of the evolution of different genes in the C₄ photosynthetic pathway and confirmed that the specific high expression in the leaf and appropriate intracellular distribution were the keys to the evolution of C₄ photosynthesis. The results of this study will help determine the evolutionary mechanism of the C₄ photosynthetic pathway in Gramineae and provide references for the transformation of C₄ photosynthetic pathways in wheat, rice, and other major C₃ cereal crops.

Genome-wide identification, expression profile and evolutionary relationships of TPS genes in the neotropical fruit tree species Psidium cattleyanum

Terpenoids are essential for plant growth, development, defense, and adaptation mechanisms. Psidium cattleyanum (Myrtaceae) is a fleshy fruit tree species endemics from Atlantic Forest, known for its pleasant fragrance and sweet taste, attributed to terpenoids in its leaves and fruits. In this study, we conducted genome-wide identification, evolutionary and expression analyses of the terpene synthase gene (TPS) family in P. cattleyanum red guava (var. cattleyanum), and yellow guava (var. lucidum Hort.) morphotypes. We identified 32 full-length TPS in red guava (RedTPS) and 30 in yellow guava (YlwTPS). We showed different expression patterns of TPS paralogous in the two morphotypes, suggesting the existence of distinct gene regulation mechanisms and their influence on the final essential oil content in both morphotypes. Moreover, the oil profile of red guava was dominated by 1,8-cineole and linalool and yellow guava was enriched in α-pinene, coincident in proportion to TPS-b1 genes, which encode enzymes that produce cyclic monoterpenes, suggesting a lineage-specific subfamily expansion of this family. Finally, we identified amino acid residues near the catalytic center and functional areas under positive selection. Our findings provide valuable insights into the terpene biosynthesis in a Neotropical Myrtaceae species and their potential involvement in adaptation mechanisms.

The genomes of medicinal skullcaps reveal the polyphyletic origins of clerodane diterpene biosynthesis in the family Lamiaceae

The presence of anticancer clerodane diterpenoids is a chemotaxonomic marker for the traditional Chinese medicinal plant Scutellaria barbata, although the molecular mechanisms behind clerodane biosynthesis are unknown. Here, we report a high-quality assembly of the 414.98 Mb genome of S. barbata into 13 pseudochromosomes. Using phylogenomic and biochemical data, we mapped the plastidial metabolism of kaurene (gibberellins), abietane, and clerodane diterpenes in three species of the family Lamiaceae (Scutellaria barbata, Scutellaria baicalensis, and Salvia splendens), facilitating the identification of genes involved in the biosynthesis of the clerodanes, kolavenol, and isokolavenol. We show that clerodane biosynthesis evolved through recruitment and neofunctionalization of genes from gibberellin and abietane metabolism. Despite the assumed monophyletic origin of clerodane biosynthesis, which is widespread in species of the Lamiaceae, our data show distinct evolutionary lineages and suggest polyphyletic origins of clerodane biosynthesis in the family Lamiaceae. Our study not only provides significant insights into the evolution of clerodane biosynthetic pathways in the mint family, Lamiaceae, but also will facilitate the production of anticancer clerodanes through future metabolic engineering efforts.

Redundant targeting signals of the apicoplast-resident protein TgMnmA in Toxoplasma gondii involve trans-organellar function

The apicoplast, which is the result of secondary endosymbiosis, is a distinctive subcellular organelle and a crucial therapeutic target for apicomplexan parasites. The majority of apicoplast-resident proteins are encoded by the nuclear genome and target the apicoplast via bipartite targeting signals consisting of a signal peptide and a transit peptide. The properties and functions of these peptides are poorly understood, which hinders the identification of apicoplast proteins and the study for plastid evolution. Here, the targeting signals of the recently discovered apicoplast tRNA thiouridylase TgMnmA of Toxoplasma gondii were analyzed. Our data using a reporter (the enhanced green fluorescent protein) fused with individual fragments containing various numbers of its N-terminal amino acids unequivocally revealed that the first 28 amino acids of TgMnmA functioned as a signal peptide for cellular secretion. The N-terminal 150 amino acids were sufficient to direct the fusion protein to the apicoplast, whereas its deletion caused the fusion protein to be localized to the mitochondrion. Our data further demonstrated that the apicoplast, rhoptry, and mitochondrion shared similar targeting signals, indicating that the apicoplast localization peptide was trans-organellar in function. In addition, the apicoplast localization peptide was important for the healthy proliferation of tachyzoites. In conclusion, the targeting signals of the nucleus-encoded apicoplast-targeted protein TgMnmA have been mapped out and the importance of this localization peptide has been elucidated in the current study.

The PRK/Rubisco shunt strongly influences Arabidopsis seed metabolism and oil accumulation, affecting more than carbon recycling

The carbon efficiency of storage lipid biosynthesis from imported sucrose in green Brassicaceae seeds is proposed to be enhanced by the PRK/Rubisco shunt, in which ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) acts outside the context of the Calvin-Benson-Bassham cycle to recycle CO2 molecules released during fatty acid synthesis. This pathway utilizes metabolites generated by the nonoxidative steps of the pentose phosphate pathway. Photosynthesis provides energy for reactions such as the phosphorylation of ribulose 5-phosphate by phosphoribulokinase (PRK). Here, we show that loss of PRK in Arabidopsis thaliana (Arabidopsis) blocks photoautotrophic growth and is seedling-lethal. However, seeds containing prk embryos develop normally, allowing us to use genetics to assess the importance of the PRK/Rubisco shunt. Compared with nonmutant siblings, prk embryos produce one-third less lipids-a greater reduction than expected from simply blocking the proposed PRK/Rubisco shunt. However, developing prk seeds are also chlorotic and have elevated starch contents compared with their siblings, indicative of secondary effects. Overexpressing PRK did not increase embryo lipid content, but metabolite profiling suggested that Rubisco activity becomes limiting. Overall, our findings show that the PRK/Rubisco shunt is tightly integrated into the carbon metabolism of green Arabidopsis seeds, and that its manipulation affects seed glycolysis, starch metabolism, and photosynthesis.

A glutathione-independent DJ-1/PfpI domain-containing tomato glyoxalaseIII2, SlGLYIII2, confers enhanced tolerance under salt and osmotic stresses

In plants, glyoxalase enzymes are activated under stress conditions to mitigate the toxic effects of hyperaccumulated methylglyoxal (MG), a highly reactive carbonyl compound. Until recently, a glutathione-dependent bi-enzymatic pathway involving glyoxalase I (GLYI) and glyoxalase II (GLYII) was considered the primary MG-detoxification system. Recently, a new glutathione-independent glyoxalase III (GLYIII) mediated direct route was also reported in plants. However, the physiological significance of this new pathway remains to be elucidated across plant species. This study identified the full complement of 22 glyoxalases in tomato. Based on their strong induction under multiple abiotic stresses, SlGLYI4, SlGLYII2 and SlGLYIII2 were selected candidates for further functional characterisation. Stress-inducible overexpression of both glutathione-dependent (SlGLYI4 + SlGLYII2) and independent (SlGLYIII2) pathways led to enhanced tolerance in both sets of transgenic plants under abiotic stresses. However, SlGLYIII2 overexpression (OE) plants outperformed the SlGLYI4 + SlGLYII2 OE counterparts for their stress tolerance under abiotic stresses. Further, knockdown of SlGLYIII2 resulted in plants with exacerbated stress responses than those silenced for both SlGLYI4 and SlGLYII2. The superior performance of SlGLYIII2 OE tomato plants for better growth and yield under salt and osmotic treatments could be attributed to better GSH/GSSG ratio, lower reactive oxygen species levels, and enhanced antioxidant potential, indicating a prominent role of GLYIII MG-detoxification pathway in abiotic stress mitigation in this species.

Genome-Wide Identification and Functional Characterization of Stress Related Glyoxalase Genes in Brassica napus L

Rapeseed (Brassica napus L.) is not only one of the most important oil crops in the world, but it is also an important vegetable crop with a high value nutrients and metabolites. However, rapeseed is often severely damaged by adverse stresses, such as low temperature, pathogen infection and so on. Glyoxalase I (GLYI) and glyoxalase II (GLYII) are two enzymes responsible for the detoxification of a cytotoxic metabolite methylglyoxal (MG) into the nontoxic S-D-lactoylglutathione, which plays crucial roles in stress tolerance in plants. Considering the important roles of glyoxalases, the GLY gene families have been analyzed in higher plans, such as rice, soybean and Chinese cabbage; however, little is known about the presence, distribution, localizations and expression of glyoxalase genes in rapeseed, a young allotetraploid. In this study, a total of 35 BnaGLYI and 30 BnaGLYII genes were identified in the B. napus genome and were clustered into six and eight subfamilies, respectively. The classification, chromosomal distribution, gene structure and conserved motif were identified or predicted. BnaGLYI and BnaGLYII proteins were mainly localized in chloroplast and cytoplasm. By using publicly available RNA-seq data and a quantitative real-time PCR analysis (qRT-PCR), the expression profiling of these genes of different tissues was demonstrated in different developmental stages as well as under stresses. The results indicated that their expression profiles varied among different tissues. Some members are highly expressed in specific tissues, BnaGLYI11 and BnaGLYI27 expressed in flowers and germinating seed. At the same time, the two genes were significantly up-regulated under heat, cold and freezing stresses. Notably, a number of BnaGLY genes showed responses to Plasmodiophora brassicae infection. Overexpression of BnGLYI11 gene in Arabidopsis thaliana seedlings confirmed that this gene conferred freezing tolerance. This study provides insight of the BnaGLYI and BnaGLYII gene families in allotetraploid B. napus and their roles in stress resistance, and important information and gene resources for developing stress resistant vegetable and rapeseed oil.

Photosynthesis in rice is increased by CRISPR/Cas9-mediated transformation of two truncated light-harvesting antenna

Plants compete for light partly by over-producing chlorophyll in leaves. The resulting high light absorption is an effective strategy for out competing neighbors in mixed communities, but it prevents light transmission to lower leaves and limits photosynthesis in dense agricultural canopies. We used a CRISPR/Cas9-mediated approach to engineer rice plants with truncated light-harvesting antenna (TLA) via knockout mutations to individual antenna assembly component genes CpSRP43, CpSRP54a, and its paralog, CpSRP54b. We compared the photosynthetic contributions of these components in rice by studying the growth rates of whole plants, quantum yield of photosynthesis, chlorophyll density and distribution, and phenotypic abnormalities. Additionally, we investigated a Poales-specific duplication of CpSRP54. The Poales are an important family that includes staple crops such as rice, wheat, corn, millet, and sorghum. Mutations in any of these three genes involved in antenna assembly decreased chlorophyll content and light absorption and increased photosynthesis per photon absorbed (quantum yield). These results have significant implications for the improvement of high leaf-area-index crop monocultures.

The thylakoid membrane protein NTA1 is an assembly factor of the cytochrome b6f complex essential for chloroplast development in Arabidopsis

The cytochrome b_6f (Cyt b_6f) complex is a multisubunit protein complex in chloroplast thylakoid membranes required for photosynthetic electron transport. Here we report the isolation and characterization of the new tiny albino 1 (nta1) mutant in Arabidopsis, which has severe defects in Cyt b_6f accumulation and chloroplast development. Gene cloning revealed that the nta1 phenotype was caused by disruption of a single nuclear gene, NTA1, which encodes an integral thylakoid membrane protein conserved across green algae and plants. Overexpression of NTA1 completely rescued the nta1 phenotype, and knockout of NTA1 in wild-type plants recapitulated the mutant phenotype. Loss of NTA1 function severely impaired the accumulation of multiprotein complexes related to photosynthesis in thylakoid membranes, particularly the components of Cyt b_6f. NTA1 was shown to directly interact with four subunits (Cyt b₆/PetB, PetD, PetG, and PetN) of Cyt b_6f through the DUF1279 domain and C-terminal sequence to mediate their assembly. Taken together, our results identify NTA1 as a new and key regulator of chloroplast development that plays essential roles in assembly of the Cyt b_6f complex by interacting with multiple Cyt b_6f subunits.

ZAXINONE SYNTHASE 2 regulates growth and arbuscular mycorrhizal symbiosis in rice

Carotenoid cleavage, catalyzed by CAROTENOID CLEAVAGE DIOXYGENASEs (CCDs), provides signaling molecules and precursors of plant hormones. Recently, we showed that zaxinone, a apocarotenoid metabolite formed by the CCD ZAXINONE SYNTHASE (ZAS), is a growth regulator required for normal rice (Oryza sativa) growth and development. The rice genome encodes three OsZAS homologs, called here OsZAS1b, OsZAS1c, and OsZAS2, with unknown functions. Here, we investigated the enzymatic activity, expression pattern, and subcellular localization of OsZAS2 and generated and characterized loss-of-function CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats and associated protein 9)-Oszas2 mutants. We show that OsZAS2 formed zaxinone in vitro. OsZAS2 was predominantly localized in plastids and mainly expressed under phosphate starvation. Moreover, OsZAS2 expression increased during mycorrhization, specifically in arbuscule-containing cells. Oszas2 mutants contained lower zaxinone content in roots and exhibited reduced root and shoot biomass, fewer tillers, and higher strigolactone (SL) levels. Exogenous zaxinone application repressed SL biosynthesis and partially rescued the growth retardation of the Oszas2 mutant. Consistent with the OsZAS2 expression pattern, Oszas2 mutants displayed a lower frequency of arbuscular mycorrhizal colonization. In conclusion, OsZAS2 is a zaxinone-forming enzyme that, similar to the previously reported OsZAS, determines rice growth, architecture, and SL content, and is required for optimal mycorrhization.

CGL160-mediated recruitment of the coupling factor CF1 is required for efficient thylakoid ATP synthase assembly, photosynthesis, and chloroplast development in Arabidopsis

Chloroplast ATP synthases consist of a membrane-spanning coupling factor (CFO) and a soluble coupling factor (CF1). It was previously demonstrated that CONSERVED ONLY IN THE GREEN LINEAGE160 (CGL160) promotes the formation of plant CFO and performs a similar function in the assembly of its c-ring to that of the distantly related bacterial Atp1/UncI protein. Here, we show that in Arabidopsis (Arabidopsis thaliana) the N-terminal portion of CGL160 (AtCGL160N) is required for late steps in CF1-CFO assembly. In plants that lacked AtCGL160N, CF1-CFO content, photosynthesis, and chloroplast development were impaired. Loss of AtCGL160N did not perturb c-ring formation, but led to a 10-fold increase in the numbers of stromal CF1 subcomplexes relative to that in the wild type. Co-immunoprecipitation and protein crosslinking assays revealed an association of AtCGL160 with CF1 subunits. Yeast two-hybrid assays localized the interaction to a stretch of AtCGL160N that binds to the DELSEED-containing CF1-β subdomain. Since Atp1 of Synechocystis (Synechocystis sp. PCC 6803) could functionally replace the membrane domain of AtCGL160 in Arabidopsis, we propose that CGL160 evolved from a cyanobacterial ancestor and acquired an additional function in the recruitment of a soluble CF1 subcomplex, which is critical for the modulation of CF1-CFO activity and photosynthesis.

Vaxi-DL: An Artificial Intelligence-Enabled Platform for Vaccine Development

Vaccine development is a complex and long process. It involves several steps, including computational studies, experimental analyses, animal model system studies, and clinical trials. This process can be accelerated by using in silico antigen screening to identify potential vaccine candidates. In this chapter, we describe a deep learning-based technique which utilizes 18 biological and 9154 physicochemical properties of proteins for finding potential vaccine candidates. Using this technique, a new web-based system, named Vaxi-DL, was developed which helped in finding new vaccine candidates from bacteria, protozoa, viruses, and fungi. Vaxi-DL is available at: https://vac.kamalrawal.in/vaxidl/ .

Short-term response to iron resupply in an iron-limited open ocean diatom reveals rapid decay of iron-responsive transcripts

In large areas of the ocean, iron concentrations are insufficient to promote phytoplankton growth. Numerous studies have been conducted to characterize the effect of iron on algae and how algae cope with fluctuating iron concentrations. Fertilization experiments in low-iron areas resulted primarily in diatom-dominated algal blooms, leading to laboratory studies on diatoms comparing low- and high-iron conditions. Here, we focus on the short-term temporal response following iron addition to an iron-starved open ocean diatom, Thalassiosira oceanica. We employed the NanoString platform and analyzed a high-resolution time series on 54 transcripts encoding proteins involved in photosynthesis, N-linked glycosylation, iron transport, as well as transcription factors. Nine transcripts were iron-responsive, with an immediate response to the addition of iron. The fastest response observed was the decrease in transcript levels of proteins involved in iron uptake, followed by an increase in transcript levels of iron-containing enzymes and a simultaneous decrease in the transcript levels of their iron-free replacement enzymes. The transcription inhibitor actinomycin D was used to understand the underlying mechanisms of the decrease of the iron-responsive transcripts and to determine their half-lives. Here, Mn-superoxide dismutase (Mn-SOD), plastocyanin (PETE), ferredoxin (PETF) and cellular repressor of EA1-stimulated genes (CREGx2) revealed longer than average half-lives. Four iron-responsive transcripts showed statistically significant differences in their decay rates between the iron-recovery samples and the actD treatment. These differences suggest regulatory mechanisms influencing gene transcription and mRNA stability. Overall, our study contributes towards a detailed understanding of diatom cell biology in the context of iron fertilization response and provides important observations to assess oceanic diatom responses following sudden changes in iron concentrations.

Biosynthesis of cannabinoid precursor olivetolic acid in genetically engineered Yarrowia lipolytica

Engineering microbes to produce plant-derived natural products provides an alternate solution to obtain bioactive products. Here we report a systematic approach to sequentially identify the rate-limiting steps and improve the biosynthesis of the cannabinoid precursor olivetolic acid (OLA) in Yarrowia lipolytica. We find that Pseudomonas sp LvaE encoding a short-chain acyl-CoA synthetase can efficiently convert hexanoic acid to hexanoyl-CoA. The co-expression of the acetyl-CoA carboxylase, the pyruvate dehydrogenase bypass, the NADPH-generating malic enzyme, as well as the activation of peroxisomal β-oxidation pathway and ATP export pathway are effective strategies to redirect carbon flux toward OLA synthesis. Implementation of these strategies led to an 83-fold increase in OLA titer, reaching 9.18 mg/L of OLA in shake flask culture. This work may serve as a baseline for engineering cannabinoids biosynthesis in oleaginous yeast species.

Identification and characterization of three nearly identical linalool/nerolidol synthase from Acorus calamus

Acorus calamus is a perennial aromatic medicinal plant from the Acorusaceae family, known for its pharmaceutical and medicinal value. A combined chemical, biochemical, and molecular study was conducted to evaluate the differential accumulation of volatile organic compounds (VOCs) in rhizomes and leaves of A. calamus essential oil. Here, we performed VOC profiling and transcriptome-based identification and functional characterization of terpene synthase (TPS) genes. A total of 110 VOCs were detected from the rhizomes and leaves of A. calamus, and some VOCs showed significant differences between them. The further transcriptome-based analysis led to the identification of six putative TPSs genes. In phylogenetic analysis, three TPSs belonged to the TPS-g clade, one to each of the TPS-a, TPS-c, and TPS-e clades. The heterologous E. coli-based expression of recombinant TPSs identified three genes (AcTPS3, AcTPS4, and AcTPS5) as bifunctional linalool/nerolidol synthase. The correlation of TPS gene expression and VOC metabolite profiles supported the function of these genes in A. calamus. Our findings provide a roadmap for future efforts to enhance the molecular mechanisms of terpene biosynthesis and our understanding of Acorus-insect interactions.

Identification and functional characterization of a γ-terpinene synthase in Nigella sativa L (black cumin)

Nigella sativa (Black cumin) has many applications in food and pharmaceutical industries. Thymoquinone has been considered as a main effective compound in N. sativa seeds and attracted researchers' attention mainly due to its medicinal potential. In this study, the essential oil components of leaves, flowers and seed developmental stages including half black seeds, soft black seeds and hard black seeds were analyzed in N. sativa. Whereas no terpenes were detected in flowers and leaves, seeds showed an essential oil composition that increased in its thymoquinone content during seed maturation. To study the proposed first step of thymoquinone biosynthesis, the formation of γ-terpinene from geranyl diphosphate (GDP), we identified and functionally characterized a γ-terpinene synthase (NsTPS1) in N. sativa. This monoterpene synthase was identified in RNA sequence data derived from seeds. After heterologous expression in Escherichia coli, partially purified NsTPS1 converted GDP to γ-terpinene. NsTPS1 is the first functionally characterized terpene synthase from N. sativa and displays a higher similarity to other terpene synthases from Ranunculaceae than known γ-terpinene synthases from more distant plant species. Characterization of NsTPS1 elucidates the first dedicated step in the biosynthesis of thymoquinone in N. sativa and paves the way towards metabolic engineering for high-level thymoquinone production.

Carbonic anhydrase isoforms of Neopyropia yezoensis: Intracellular localization and expression profiles in response to inorganic carbon concentration and life stage

Macroalgae, particularly commercially grown seaweed, substantially contribute to CO₂ removal and carbon storage. However, knowledge regarding the CO₂ concentrating mechanism (CCM) of macroalgae is limited. Carbonic anhydrase (CA), a key component of the biophysical CCM, plays important roles in many physiological reactions in various organisms. Few characteristics of CA in Neopyropia yezoensis are known, particularly its intracellular location and responses to different concentrations of Ci. We identified, amplified, and characterized 11 putative genes encoding N. yezoensis CA. The predicted corresponding proteins clustered into three subfamilies: α-, β-, and γ-type. The intracellular localization of seven CA isoforms-one in the chloroplasts, three in the cytoplasm, and three in the mitochondria-was elucidated with fusion proteins. Higher NyCA expression, particularly of certain chloroplastic, cytosolic, and mitochondrial CAs, is observed more often during the foliose stage, thus suggesting that CAs play important roles in development in N. yezoensis.

Expression of nuclear-encoded, haptophyte-derived ftsH genes support extremely rapid PSII repair and high-light photoacclimation in Karenia brevis (Dinophyceae)

Karenia brevis, a neurotoxic dinoflagellate that produces brevetoxins, is endemic to the Gulf of Mexico and can grow at high irradiances typical of surface waters found there. To build upon a growing number of studies addressing high-light tolerance in K. brevis, specific photobiology and molecular mechanisms underlying this capacity were evaluated in culture. Since photosystem II (PSII) repair cycle activity can be crucial to high light tolerance in plants and algae, the present study assessed this capacity in K. brevis and characterized the ftsH-like genes which are fundamental to this process. Compared with cultures grown in low-light, cultures grown in high-light showed a 65-fold increase in PSII photoinactivation, a ∼50-fold increase in PSII repair, enhanced nonphotochemical quenching (NPQ), and depressed F_v/F_m. Repair rates were among the fastest reported in phytoplankton. Publicly available K. brevis transcriptomes (MMETSP) were queried for ftsH-like sequences and refined with additional sequencing from two K. brevis strains. The genes were phylogenetically related to haptophyte orthologs, implicating acquisition during tertiary endosymbiosis. RT-qPCR of three of the four ftsH-like homologs revealed that poly-A tails predominated in all homologs, and that the most highly expressed homolog had a 5' splice leader and amino-acid motifs characteristic of chloroplast targeting, indicating nuclear encoding for this plastid-targeted gene. High-light cultures showed a ∼1.5-fold upregulation in mRNA expression of the thylakoid-associated genes. Overall, in conjunction with NPQ mechanisms, rapid PSII repair mediated by a haptophyte-derived ftsH prevents chronic photoinhibition in K. brevis. Our findings continue to build the case that high-light photobiology-supported by the acquisition and maintenance of tertiary endosymbiotic genes-is critical to the success of K. brevis in the Gulf of Mexico.