Deregulation of phenylalanine biosynthesis evolved with the emergence of vascular plants.

Phenylalanine (Phe) is the precursor of essential secondary products in plants. Here we show that a key, rate-limiting step in Phe biosynthesis, which is catalyzed by arogenate dehydratase, experienced feedback de-regulation during evolution. Enzymes from microorganisms and type-I ADTs from plants are strongly feedback-inhibited by Phe, while type-II isoforms remain active at high levels of Phe. We have found that type-II ADTs are widespread across seed plants and their overproduction resulted in a dramatic accumulation of Phe in planta, reaching levels up to 40 times higher than those observed following the expression of type-I enzymes. Punctual changes in the allosteric binding site of Phe and adjacent region are responsible for the observed relaxed regulation. The phylogeny of plant ADTs evidences that the emergence of type-II isoforms with relaxed regulation occurred at some point in the transition between nonvascular plants and tracheophytes, enabling the massive production of Phe-derived compounds, primarily lignin, a hallmark of vascular plants.

Oxidative stress responses after exposure to triclosan sublethal concentrations: an integrated biomarker approach with a native (Corydoras paleatus) and a model fish species (Danio rerio).

Triclosan (TCS) is a synthetic broad-spectrum antimicrobial agent commonly used world-wide in a range of personal care and sanitizing products detected frequently in aquatic ecosystems. The aim of this study was to examine biochemical markers responses triggered by TCS in Danio rerio and in a native South American fish species (Corydoras paleatus). Further, an integrated approach comparing both test fish species was undertaken. These fish organisms were exposed to 100 or 189 µg TCS/L for 48 h. The activities of catalase (CAT), glutathione-s-transferase (GST), superoxide dismutase (SOD), and lipid peroxidation levels (LPO) and total antioxidant capacity against peroxyl radicals (ACAP) were determined in liver, gills, and brain. Acetylcholinesterase activity (AChE) was measured in the brain. Multivariate analysis showed that the most sensitive hepatic parameters were activities of GST and SOD for C. paleatus while LPO levels were for D. rerio. In gills the same parameters were responsive for C. paleatus but CAT in D. rerio. ACAP and GST activity were responsive parameters in brain of both species. Integrated biomarker responses (IBR) index demonstrated similar trends in both species suggesting this parameter might serve as a useful tool for quantification of integrated responses induced by TCS.

Multibiomarker responses and bioaccumulation of fipronil in Prochilodus lineatus exposed to spiked sediments: Oxidative stress and antioxidant defenses.

Fipronil is a current use pesticide, widely used in many crops, commonly adsorbed to sediments of aquatic environments. The purpose of this study was to evaluate the biomarker responses and fipronil distribution pattern in different matrixes (fish, sediment and water) after juveniles P. lineatus exposure at two environmental concentrations (5.5 and 82 µg kg--1) of fipronil-spiked sediments. The levels of oxidized proteins (PO), lipid peroxidation (LPO), and enzymatic activity of superoxide dismutase (SOD), reduced glutathione content (GSH), antioxidant capacity against peroxyls (ACAP) and acetylcholinesterase (AChE) were evaluated in liver, gills and brain. Concentrations of fipronil and its metabolites (f. desulfinyl, f sulphpHide and f. sulfone) were quantified by GC-ECD. F. desulfinyl was the major metabolite found in all matrixes, followed by f. sulphide in sediments, while f. sulfone was mainly accumulated in fish. Fipronil promoted oxidative stress in P. lineatus, as evidenced by the increases in LPO and PO levels and the decrease brain AChE activity. Fish exposed at both concentrations showed significant decrease in antioxidant capacity. Alterations in the antioxidant defenses system was evidenced in all organs. These results suggest that the occurrence of fipronil in aquatic environments can generate oxidative stress at different levels in P. lineatus, showing that this species is highly sensitive to the deleterious effects of fipronil and metabolites.

Nanosilver and Silver Nitrate Toxicity in Ex Vivo-Exposed Gills of Fish and Mitigation by Humic Acids.

Silver nanoparticles (AgNP) are unique because of their biocide properties. Once released to environment, AgNP interact with the natural organic matter which impact on their fate, dispersion, and ultimate toxicity. We carried out an ex vivo exposure of gill of Corydoras paleatus fish to 100 µg L-1 of AgNP or AgNO3, alone and in combination with 10 mg L-1 of humic acids (HA), with the aim to evaluate the potential mitigation of HA on AgNP toxic effects. We analyzed Ag accumulation and oxidative stress biomarkers. The results showed high bioaccumulation after the AgNO3+HA exposure. An inhibition of glutathione-S-transferase enzymatic activity and depletion of reduced glutathione levels were registered after the AgNO3 exposure, and increased lipid peroxidation levels in the case of AgNP one. Oxidative responses were mitigated when the HA were present in the media. Overall, the knowledge about the fate of this emergent pollutant was deepened through this study.

Transcriptional analysis of arogenate dehydratase genes identifies a link between phenylalanine biosynthesis and lignin biosynthesis.

Biogenesis of the secondary cell wall in trees involves the massive biosynthesis of the phenylalanine-derived polymer lignin. Arogenate dehydratase (ADT) catalyzes the last, and rate-limiting, step of the main pathway for phenylalanine biosynthesis. In this study, we found that transcript levels for several members of the large ADT gene family, including ADT-A and ADT-D, were enhanced in compression wood of maritime pine, a xylem tissue enriched in lignin. Transcriptomic analysis of maritime pine silenced for PpMYB8 revealed that this gene plays a critical role in coordinating the deposition of lignin with the biosynthesis of phenylalanine. Specifically, it was found that ADT-A and ADT-D were strongly down-regulated in PpMYB8-silenced plants and that they were transcriptionally regulated through direct interaction of this transcription factor with regulatory elements present in their promoters. Another transcription factor, PpHY5, exhibited an expression profile opposite to that of PpMYB8 and also interacted with specific regulatory elements of ADT-A and ADT-D genes, suggesting that it is involved in transcriptional regulation of phenylalanine biosynthesis. Taken together, our results reveal that PpMYB8 and PpHY5 are involved in the control of phenylalanine formation and its metabolic channeling for lignin biosynthesis and deposition during wood formation in maritime pine.

Parkinson's Disease Tremor Detection in the Wild Using Wearable Accelerometers.

Continuous in-home monitoring of Parkinson's Disease (PD) symptoms might allow improvements in assessment of disease progression and treatment effects. As a first step towards this goal, we evaluate the feasibility of a wrist-worn wearable accelerometer system to detect PD tremor in the wild (uncontrolled scenarios). We evaluate the performance of several feature sets and classification algorithms for robust PD tremor detection in laboratory and wild settings. We report results for both laboratory data with accurate labels and wild data with weak labels. The best performance was obtained using a combination of a pre-processing module to extract information from the tremor spectrum (based on non-negative factorization) and a deep neural network for learning relevant features and detecting tremor segments. We show how the proposed method is able to predict patient self-report measures, and we propose a new metric for monitoring PD tremor (i.e., percentage of tremor over long periods of time), which may be easier to estimate the start and end time points of each tremor event while still providing clinically useful information.

Learning Facial Action Units with Spatiotemporal Cues and Multi-label Sampling.

Facial action units (AUs) may be represented spatially, temporally, and in terms of their correlation. Previous research focuses on one or another of these aspects or addresses them disjointly. We propose a hybrid network architecture that jointly models spatial and temporal representations and their correlation. In particular, we use a Convolutional Neural Network (CNN) to learn spatial representations, and a Long Short-Term Memory (LSTM) to model temporal dependencies among them. The outputs of CNNs and LSTMs are aggregated into a fusion network to produce per-frame prediction of multiple AUs. The hybrid network was compared to previous state-of-the-art approaches in two large FACS-coded video databases, GFT and BP4D, with over 400,000 AU-coded frames of spontaneous facial behavior in varied social contexts. Relative to standard multi-label CNN and feature-based state-of-the-art approaches, the hybrid system reduced person-specific biases and obtained increased accuracy for AU detection. To address class imbalance within and between batches during training the network, we introduce multi-labeling sampling strategies that further increase accuracy when AUs are relatively sparse. Finally, we provide visualization of the learned AU models, which, to the best of our best knowledge, reveal for the first time how machines see AUs.

The Functional Characterization of Podosphaera xanthii Candidate Effector Genes Reveals Novel Target Functions for Fungal Pathogenicity.

Podosphaera xanthii is the main causal agent of powdery mildew disease in cucurbits. In a previous study, we determined that P. xanthii expresses approximately 50 Podosphaera effector candidates (PECs), identified based on the presence of a predicted signal peptide and the absence of functional annotation. In this work, we used host-induced gene silencing (HIGS), employing Agrobacterium tumefaciens as a vector for the delivery of the silencing constructs (ATM-HIGS), to identify genes involved in early plant-pathogen interaction. The analysis of seven selected PEC-encoding genes showed that six of them, PEC007, PEC009, PEC019, PEC032, PEC034, and PEC054, are required for P. xanthii pathogenesis, as revealed by reduced fungal growth and increased production of hydrogen peroxide by host cells. In addition, protein models and protein-ligand predictions allowed us to identify putative functions for these candidates. The biochemical activities of PEC019, PEC032, and PEC054 were elucidated using their corresponding proteins expressed in Escherichia coli. These proteins were confirmed as phospholipid-binding protein, α-mannosidase, and cellulose-binding protein. Further, BLAST searches showed that these three effectors are widely distributed in phytopathogenic fungi. These results suggest novel targets for fungal effectors, such as host-cell plasma membrane, host-cell glycosylation, and damage-associated molecular pattern-triggered immunity.

The Arogenate Dehydratase ADT2 is Essential for Seed Development in Arabidopsis.

Phenylalanine (Phe) biosynthesis in plants is a key process, as Phe serves as a precursor of proteins and phenylpropanoids. The prephenate pathway connects chorismate, the final product of the shikimate pathway, with the biosynthesis of Phe and tyrosine. Two alternative routes of Phe biosynthesis have been reported: one depending on arogenate, and the other on phenylpyruvate. Whereas the arogenate pathway is considered the main route, the role of the phenylpyruvate pathway remains unclear. Here, we report that a deficiency in ADT2, a bifunctional arogenate dehydratase (ADT)/prephenate dehydratase (PDT) enzyme, causes embryo arrest and seed abortion. This result makes a clear distinction between the essential role of ADT2 and the five remaining ADT genes from Arabidopsis, which display mostly overlapping functions. We have found that PHA2, a monofunctional PDT from yeast, restores the adt2 phenotype when it is targeted within the plastids, but not when is expressed in the cytosol. Similar results can be obtained by expressing ADT3, a monofunctional ADT. These results suggest that Phe can be synthesized from phenylpyruvate or arogenate when the bifunctional ADT2 is replaced by other ADT or PDT enzymes during seed formation, highlighting the importance of Phe biosynthesis for embryo development, and providing further insights into the plasticity of Phe biosynthesis.

A Universal Stress Protein Involved in Oxidative Stress Is a Phosphorylation Target for Protein Kinase CIPK6.

Calcineurin B-like interacting protein kinases (CIPKs) decode calcium signals upon interaction with the calcium sensors calcineurin B like proteins into phosphorylation events that result into adaptation to environmental stresses. Few phosphorylation targets of CIPKs are known and therefore the molecular mechanisms underlying their downstream output responses are not fully understood. Tomato (Solanum lycopersicum) Cipk6 regulates immune and susceptible Programmed cell death in immunity transforming Ca2+ signals into reactive oxygen species (ROS) signaling. To investigate SlCipk6-induced molecular mechanisms and identify putative substrates, a yeast two-hybrid approach was carried on and a protein was identified that contained a Universal stress protein (Usp) domain present in bacteria, protozoa and plants, which we named "SlRd2". SlRd2 was an ATP-binding protein that formed homodimers in planta. SlCipk6 and SlRd2 interacted using coimmunoprecipitation and bimolecular fluorescence complementation (BiFC) assays in Nicotiana benthamiana leaves and the complex localized in the cytosol. SlCipk6 phosphorylated SlRd2 in vitro, thus defining, to our knowledge, a novel target for CIPKs. Heterologous SlRd2 overexpression in yeast conferred resistance to highly toxic LiCl, whereas SlRd2 expression in Escherichia coli UspA mutant restored bacterial viability in response to H2O2 treatment. Finally, transient expression of SlCipk6 in transgenic N benthamiana SlRd2 overexpressors resulted in reduced ROS accumulation as compared to wild-type plants. Taken together, our results establish that SlRd2, a tomato UspA, is, to our knowledge, a novel interactor and phosphorylation target of a member of the CIPK family, SlCipk6, and functionally regulates SlCipk6-mediated ROS generation.

Identification of a small protein domain present in all plant lineages that confers high prephenate dehydratase activity.

l-Phenylalanine serves as a building block for the biosynthesis of proteins, but also as a precursor for a wide range of plant-derived compounds essential for plants and animals. Plants can synthesize Phe within the plastids using arogenate as a precursor; however, an alternative pathway using phenylpyruvate as an intermediate, described for most microorganisms, has recently been proposed. The functionality of this pathway requires the existence of enzymes with prephenate dehydratase (PDT) activity (EC 4.2.1.51) in plants. Using phylogenetic studies, functional complementation assays in yeast and biochemical analysis, we have identified the enzymes displaying PDT activity in Pinus pinaster. Through sequence alignment comparisons and site-directed mutagenesis we have identified a 22-amino acid region conferring PDT activity (PAC domain) and a single Ala314 residue critical to trigger this activity. Our results demonstrate that all plant clades include PAC domain-containing ADTs, suggesting that the PDT activity, and thus the ability to synthesize Phe using phenylpyruvate as an intermediate, has been preserved throughout the evolution of plants. Moreover, this pathway together with the arogenate pathway gives plants a broad and versatile capacity to synthesize Phe and its derived compounds. PAC domain-containing enzymes are also present in green and red algae, and glaucophytes, the three emerging clades following the primary endosymbiont event resulting in the acquisition of plastids in eukaryotes. The evolutionary prokaryotic origin of this domain is discussed.

Molecular fundamentals of nitrogen uptake and transport in trees.

Nitrogen (N) is frequently a limiting factor for tree growth and development. Because N availability is extremely low in forest soils, trees have evolved mechanisms to acquire and transport this essential nutrient along with biotic interactions to guarantee its strict economy. Here we review recent advances in the molecular basis of tree N nutrition. The molecular characteristics, regulation, and biological significance of membrane proteins involved in the uptake and transport of N are addressed. The regulation of N uptake and transport in mycorrhized roots and transcriptome-wide studies of N nutrition are also outlined. Finally, several areas of future research are suggested.

A Branch-and-Bound Framework for Unsupervised Common Event Discovery.

Event discovery aims to discover a temporal segment of interest, such as human behavior, actions or activities. Most approaches to event discovery within or between time series use supervised learning. This becomes problematic when some relevant event labels are unknown, are difficult to detect, or not all possible combinations of events have been anticipated. To overcome these problems, this paper explores Common Event Discovery (CED), a new problem that aims to discover common events of variable-length segments in an unsupervised manner. A potential solution to CED is searching over all possible pairs of segments, which would incur a prohibitive quartic cost. In this paper, we propose an efficient branch-and-bound (B&B) framework that avoids exhaustive search while guaranteeing a globally optimal solution. To this end, we derive novel bounding functions for various commonality measures and provide extensions to multiple commonality discovery and accelerated search. The B&B framework takes as input any multidimensional signal that can be quantified into histograms. A generalization of the framework can be readily applied to discover events at the same or different times (synchrony and event commonality, respectively). We consider extensions to video search and supervised event detection. The effectiveness of the B&B framework is evaluated in motion capture of deliberate behavior and in video of spontaneous facial behavior in diverse interpersonal contexts: interviews, small groups of young adults, and parent-infant face-to-face interaction.

Clinical management, expectations, and satisfaction of patients with moderate to severe allergic rhinoconjunctivitis treated with SQ-standardized grass-allergen tablet under routine clinical practice conditions in Spain.

BACKGROUND: Sublingual immunotherapy has been proven as a well-tolerated and effective treatment for allergic rhinitis. Within this type of treatment, GRAZAX® is the most documented product in terms of safety and efficacy. The objective of this study was to identify the patients' expectations and level of treatment satisfaction, as well as the clinical management of patients with moderate/severe allergic rhinoconjunctivitis treated with GRAZAX®. METHODS: This was a non-interventional, observational, multi-centre, open-label study involving a total of 131 adult patients aged 18-66 years with confirmed diagnosis of grass-allergy and initiated treatment with GRAZAX® between June 2010 and April 2011. RESULTS: In the pollen season after starting treatment, 56.6% of patients stated that their symptoms were much less/less intense, 86% needed less symptomatic medication for control of their symptoms, and 74.4% manifested to have improved (quite/a lot) as regards their allergic disease since treatment was initiated as compared with previous grass pollen season. The patient satisfaction with GRAZAX® was measured using a visual analogue scale (VAS) between 0 (minimum satisfaction) and 100 (maximum satisfaction) comprising five different items: effectiveness, tolerability, cost, convenience and overall satisfaction. The results obtained for each item were [mean (SD)]: 74.7 (18.1), 70.3 (36.1), 39.3 (25.8), 86.2 (12.6), 78.4 (15.8) respectively. The patient's level of satisfaction is highly influenced, especially in terms of assessment of effectiveness, tolerability and convenience, by the information provided by the specialist. CONCLUSIONS: In summary, it can be concluded that improved communication leads to increased patient knowledge, greater patient compliance, and increased patient satisfaction.

The tomato calcium sensor Cbl10 and its interacting protein kinase Cipk6 define a signaling pathway in plant immunity.

Ca(2+) signaling is an early and necessary event in plant immunity. The tomato (Solanum lycopersicum) kinase Pto triggers localized programmed cell death (PCD) upon recognition of Pseudomonas syringae effectors AvrPto or AvrPtoB. In a virus-induced gene silencing screen in Nicotiana benthamiana, we independently identified two components of a Ca(2+)-signaling system, Cbl10 (for calcineurin B-like protein) and Cipk6 (for calcineurin B-like interacting protein kinase), as their silencing inhibited Pto/AvrPto-elicited PCD. N. benthamiana Cbl10 and Cipk6 are also required for PCD triggered by other plant resistance genes and virus, oomycete, and nematode effectors and for host susceptibility to two P. syringae pathogens. Tomato Cipk6 interacts with Cbl10 and its in vitro kinase activity is enhanced in the presence of Cbl10 and Ca(2+), suggesting that tomato Cbl10 and Cipk6 constitute a Ca(2+)-regulated signaling module. Overexpression of tomato Cipk6 in N. benthamiana leaves causes accumulation of reactive oxygen species (ROS), which requires the respiratory burst homolog RbohB. Tomato Cbl10 and Cipk6 interact with RbohB at the plasma membrane. Finally, Cbl10 and Cipk6 contribute to ROS generated during effector-triggered immunity in the interaction of P. syringae pv tomato DC3000 and N. benthamiana. We identify a role for the Cbl/Cipk signaling module in PCD, establishing a mechanistic link between Ca(2+) and ROS signaling in plant immunity.

A Novel Artificial Intelligence System for Endotracheal Intubation.

OBJECTIVE: Adequate visualization of the glottic opening is a key factor to successful endotracheal intubation (ETI); however, few objective tools exist to help guide providers' ETI attempts toward the glottic opening in real-time. Machine learning/artificial intelligence has helped to automate the detection of other visual structures but its utility with ETI is unknown. We sought to test the accuracy of various computer algorithms in identifying the glottic opening, creating a tool that could aid successful intubation. METHODS: We collected a convenience sample of providers who each performed ETI 10 times on a mannequin using a video laryngoscope (C-MAC, Karl Storz Corp, Tuttlingen, Germany). We recorded each attempt and reviewed one-second time intervals for the presence or absence of the glottic opening. Four different machine learning/artificial intelligence algorithms analyzed each attempt and time point: k-nearest neighbor (KNN), support vector machine (SVM), decision trees, and neural networks (NN). We used half of the videos to train the algorithms and the second half to test the accuracy, sensitivity, and specificity of each algorithm. RESULTS: We enrolled seven providers, three Emergency Medicine attendings, and four paramedic students. From the 70 total recorded laryngoscopic video attempts, we created 2,465 time intervals. The algorithms had the following sensitivity and specificity for detecting the glottic opening: KNN (70%, 90%), SVM (70%, 90%), decision trees (68%, 80%), and NN (72%, 78%). CONCLUSIONS: Initial efforts at computer algorithms using artificial intelligence are able to identify the glottic opening with over 80% accuracy. With further refinements, video laryngoscopy has the potential to provide real-time, direction feedback to the provider to help guide successful ETI.

Deciphering the role of aspartate and prephenate aminotransferase activities in plastid nitrogen metabolism.

Chloroplasts and plastids of nonphotosynthetic plant cells contain two aspartate (Asp) aminotransferases: a eukaryotic type (Asp5) and a prokaryotic-type bifunctional enzyme displaying Asp and prephenate aminotransferase activities (PAT). We have identified the entire Asp aminotransferase gene family in Nicotiana benthamiana and isolated and cloned the genes encoding the isoenzymes with plastidic localization: NbAsp5 and NbPAT. Using a virus-induced gene silencing approach, we obtained N. benthamiana plants silenced for NbAsp5 and/or NbPAT. Phenotypic and metabolic analyses were conducted in silenced plants to investigate the specific roles of these enzymes in the biosynthesis of essential amino acids within the plastid. The NbAsp5 silenced plants had no changes in phenotype, exhibiting similar levels of free Asp and glutamate as control plants, but contained diminished levels of asparagine and much higher levels of lysine. In contrast, the suppression of NbPAT led to a severe reduction in growth and strong chlorosis symptoms. NbPAT silenced plants exhibited extremely reduced levels of asparagine and were greatly affected in their phenylalanine metabolism and lignin deposition. Furthermore, NbPAT suppression triggered a transcriptional reprogramming in plastid nitrogen metabolism. Taken together, our results indicate that NbPAT has an overlapping role with NbAsp5 in the biosynthesis of Asp and a key role in the production of phenylalanine for the biosynthesis of phenylpropanoids. The analysis of NbAsp5/NbPAT cosilenced plants highlights the central role of both plastidic aminotransferases in nitrogen metabolism; however, only NbPAT is essential for plant growth and development.

Estimating smile intensity: A better way.

Both the occurrence and intensity of facial expressions are critical to what the face reveals. While much progress has been made towards the automatic detection of facial expression occurrence, controversy exists about how to estimate expression intensity. The most straight-forward approach is to train multiclass or regression models using intensity ground truth. However, collecting intensity ground truth is even more time consuming and expensive than collecting binary ground truth. As a shortcut, some researchers have proposed using the decision values of binary-trained maximum margin classifiers as a proxy for expression intensity. We provide empirical evidence that this heuristic is flawed in practice as well as in theory. Unfortunately, there are no shortcuts when it comes to estimating smile intensity: researchers must take the time to collect and train on intensity ground truth. However, if they do so, high reliability with expert human coders can be achieved. Intensity-trained multiclass and regression models outperformed binary-trained classifier decision values on smile intensity estimation across multiple databases and methods for feature extraction and dimensionality reduction. Multiclass models even outperformed binary-trained classifiers on smile occurrence detection.

Spontaneous facial expression in unscripted social interactions can be measured automatically.

Methods to assess individual facial actions have potential to shed light on important behavioral phenomena ranging from emotion and social interaction to psychological disorders and health. However, manual coding of such actions is labor intensive and requires extensive training. To date, establishing reliable automated coding of unscripted facial actions has been a daunting challenge impeding development of psychological theories and applications requiring facial expression assessment. It is therefore essential that automated coding systems be developed with enough precision and robustness to ease the burden of manual coding in challenging data involving variation in participant gender, ethnicity, head pose, speech, and occlusion. We report a major advance in automated coding of spontaneous facial actions during an unscripted social interaction involving three strangers. For each participant (n = 80, 47 % women, 15 % Nonwhite), 25 facial action units (AUs) were manually coded from video using the Facial Action Coding System. Twelve AUs occurred more than 3 % of the time and were processed using automated FACS coding. Automated coding showed very strong reliability for the proportion of time that each AU occurred (mean intraclass correlation = 0.89), and the more stringent criterion of frame-by-frame reliability was moderate to strong (mean Matthew's correlation = 0.61). With few exceptions, differences in AU detection related to gender, ethnicity, pose, and average pixel intensity were small. Fewer than 6 % of frames could be coded manually but not automatically. These findings suggest automated FACS coding has progressed sufficiently to be applied to observational research in emotion and related areas of study.

Plastidic aspartate aminotransferases and the biosynthesis of essential amino acids in plants.

In the chloroplasts and in non-green plastids of plants, aspartate is the precursor for the biosynthesis of different amino acids and derived metabolites that play distinct and important roles in plant growth, reproduction, development or defence. Aspartate biosynthesis is mediated by the enzyme aspartate aminotransferase (EC 2.6.1.1), which catalyses the reversible transamination between glutamate and oxaloacetate to generate aspartate and 2-oxoglutarate. Plastids contain two aspartate aminotransferases: a eukaryotic-type and a prokaryotic-type bifunctional enzyme displaying aspartate and prephenate aminotransferase activities. A general overview of the biochemistry, regulation, functional significance, and phylogenetic origin of both enzymes is presented. The roles of these plastidic aminotransferases in the biosynthesis of essential amino acids are discussed.