Amino Acid Catabolism in Plants.
Hildebrandt Tatjana M,Nunes Nesi Adriano,Araújo Wagner L,Braun Hans-Peter
Amino acids have various prominent functions in plants. Besides their usage during protein biosynthesis, they also represent building blocks for several other biosynthesis pathways and play pivotal roles during signaling processes as well as in plant stress response. In general, pool sizes of the 20 amino acids differ strongly and change dynamically depending on the developmental and physiological state of the plant cell. Besides amino acid biosynthesis, which has already been investigated in great detail, the catabolism of amino acids is of central importance for adjusting their pool sizes but so far has drawn much less attention. The degradation of amino acids can also contribute substantially to the energy state of plant cells under certain physiological conditions, e.g. carbon starvation. In this review, we discuss the biological role of amino acid catabolism and summarize current knowledge on amino acid degradation pathways and their regulation in the context of plant cell physiology.
Plant Phenylalanine/Tyrosine Ammonia-lyases.
Barros Jaime,Dixon Richard A
Trends in plant science
Aromatic amino acid deaminases are key enzymes mediating carbon flux from primary to secondary metabolism in plants. Recent studies have uncovered a tyrosine ammonia-lyase that contributes to the typical characteristics of grass cell walls and contributes to about 50% of the total lignin synthesized by the plant. Grasses are currently preferred bioenergy feedstocks and lignin is the most important limiting factor in the conversion of plant biomass to liquid biofuels, as well as being an abundant renewable carbon source that can be industrially exploited. Further research on the structure, evolution, regulation, and biological function of functionally distinct ammonia-lyases has multiple implications for improving the economics of the agri-food and biofuel industries.
Serine in plants: biosynthesis, metabolism, and functions.
Ros Roc,Muñoz-Bertomeu Jesús,Krueger Stephan
Trends in plant science
Serine (Ser) has a fundamental role in metabolism and signaling in living organisms. In plants, the existence of different pathways of Ser biosynthesis has complicated our understanding of this amino acid homeostasis. The photorespiratory glycolate pathway has been considered to be of major importance, whereas the nonphotorespiratory phosphorylated pathway has been relatively neglected. Recent advances indicate that the phosphorylated pathway has an important function in plant metabolism and development. Plants deficient in this pathway display developmental defects in embryos, male gametophytes, and roots. We propose that the phosphorylated pathway is more important than was initially thought because it is the only Ser source for specific cell types involved in developmental events. Here, we discuss its importance as a link between metabolism and development in plants.
The Regulation of Essential Amino Acid Synthesis and Accumulation in Plants.
Galili Gad,Amir Rachel,Fernie Alisdair R
Annual review of plant biology
Although amino acids are critical for all forms of life, only proteogenic amino acids that humans and animals cannot synthesize de novo and therefore must acquire in their diets are classified as essential. Nine amino acids-lysine, methionine, threonine, phenylalanine, tryptophan, valine, isoleucine, leucine, and histidine-fit this definition. Despite their nutritional importance, several of these amino acids are present in limiting quantities in many of the world's major crops. In recent years, a combination of reverse genetic and biochemical approaches has been used to define the genes encoding the enzymes responsible for synthesizing, degrading, and regulating these amino acids. In this review, we describe recent advances in our understanding of the metabolism of the essential amino acids, discuss approaches for enhancing their levels in plants, and appraise efforts toward their biofortification in crop plants.
Differential distribution of amino acids in plants.
Kumar Vinod,Sharma Anket,Kaur Ravdeep,Thukral Ashwani Kumar,Bhardwaj Renu,Ahmad Parvaiz
Plants are a rich source of amino acids and their individual abundance in plants is of great significance especially in terms of food. Therefore, it is of utmost necessity to create a database of the relative amino acid contents in plants as reported in literature. Since in most of the cases complete analysis of profiles of amino acids in plants was not reported, the units used and the methods applied and the plant parts used were different, amino acid contents were converted into relative units with respect to lysine for statistical analysis. The most abundant amino acids in plants are glutamic acid and aspartic acid. Pearson's correlation analysis among different amino acids showed that there were no negative correlations between the amino acids. Cluster analysis (CA) applied to relative amino acid contents of different families. Alismataceae, Cyperaceae, Capparaceae and Cactaceae families had close proximity with each other on the basis of their relative amino acid contents. First three components of principal component analysis (PCA) explained 79.5% of the total variance. Factor analysis (FA) explained four main underlying factors for amino acid analysis. Factor-1 accounted for 29.4% of the total variance and had maximum loadings on glycine, isoleucine, leucine, threonine and valine. Factor-2 explained 25.8% of the total variance and had maximum loadings on alanine, aspartic acid, serine and tyrosine. 14.2% of the total variance was explained by factor-3 and had maximum loadings on arginine and histidine. Factor-4 accounted 8.3% of the total variance and had maximum loading on the proline amino acid. The relative content of different amino acids presented in this paper is alanine (1.4), arginine (1.8), asparagine (0.7), aspartic acid (2.4), cysteine (0.5), glutamic acid (2.8), glutamine (0.6), glycine (1.0), histidine (0.5), isoleucine (0.9), leucine (1.7), lysine (1.0), methionine (0.4), phenylalanine (0.9), proline (1.1), serine (1.0), threonine (1.0), tryptophan (0.3), tyrosine (0.7) and valine (1.2).
-amino Acids in Plants: Sources, Metabolism, and Functions.
International journal of molecular sciences
Although plants are permanently exposed to -amino acids (-AAs) in the rhizosphere, these compounds were for a long time regarded as generally detrimental, due to their inhibitory effects on plant growth. Recent studies showed that this statement needs a critical revision. There were several reports of active uptake by and transport of -AAs in plants, leading to the question whether these processes happened just as side reactions or even on purpose. The identification and characterization of various transporter proteins and enzymes in plants with considerable affinities or specificities for -AAs also pointed in the direction of their targeted uptake and utilization. This attracted more interest, as -AAs were shown to be involved in different physiological processes in plants. Especially, the recent characterization of -AA stimulated ethylene production in revealed for the first time a physiological function for a specific -AA and its metabolizing enzyme in plants. This finding opened the question regarding the physiological or developmental contexts in which -AA stimulated ethylene synthesis are involved in. This question and the ones about the transport characteristics of -AAs, their metabolism, and their different physiological effects, are the focus of this review.
Amino Acid and Carbohydrate Metabolism Are Coordinated to Maintain Energetic Balance during Drought in Sugarcane.
Diniz Augusto Lima,da Silva Danielle Izilda Rodrigues,Lembke Carolina Gimiliani,Costa Maximiller Dal-Bianco Lamas,Ten-Caten Felipe,Li Forrest,Vilela Romel Duarte,Menossi Marcelo,Ware Doreen,Endres Lauricio,Souza Glaucia Mendes
International journal of molecular sciences
The ability to expand crop plantations without irrigation is a major goal to increase agriculture sustainability. To achieve this end, we need to understand the mechanisms that govern plant growth responses under drought conditions. In this study, we combined physiological, transcriptomic, and genomic data to provide a comprehensive picture of drought and recovery responses in the leaves and roots of sugarcane. Transcriptomic profiling using oligoarrays and RNA-seq identified 2898 (out of 21,902) and 46,062 (out of 373,869) transcripts as differentially expressed, respectively. Co-expression analysis revealed modules enriched in photosynthesis, small molecule metabolism, alpha-amino acid metabolism, trehalose biosynthesis, serine family amino acid metabolism, and carbohydrate transport. Together, our findings reveal that carbohydrate metabolism is coordinated with the degradation of amino acids to provide carbon skeletons to the tricarboxylic acid cycle. This coordination may help to maintain energetic balance during drought stress adaptation, facilitating recovery after the stress is alleviated. Our results shed light on candidate regulatory elements and pave the way to biotechnology strategies towards the development of drought-tolerant sugarcane plants.
Alteration of local and systemic amino acids metabolism for the inducible defense in tea plant (Camellia sinensis) in response to leaf herbivory by Ectropis oblique.
Li Longbao,Li Tingting,Jiang Yuanyuan,Yang Yunqiu,Zhang Liang,Jiang Zongde,Wei Chaoling,Wan Xiaochun,Yang Hua
Archives of biochemistry and biophysics
Leaf herbivory on tea plants (Camellia sinensis) by tea geometrids (Ectropis oblique) can cause severe yield loss and quality damage for tea. In previous work, we discovered that leaf herbivory triggered systemic carbon depletion in undamaged roots to enhance resource investment for local defense induced in damaged leaves. Here, we investigated the dynamics of amino acids in the local and systemic responses and the roles of nitrogen resource reallocation for the inducible defense in tea plants in response to leaf herbivory. The comparative analysis of the dynamics of flavonoids, caffeine, theanine and basic amino acids at metabolic and transcriptome levels revealed that leaf herbivory triggered the differential reconfiguration of these amino acid-derived defensive metabolites and nitrogenous primary metabolism between the local and systemic responses. The tight association of the metabolism and reallocation of amino acids with the activation of defensive secondary metabolism indicated that the systemic nitrogen reallocation played a potentially important role for the resource investment in tea plant resistance against leaf herbivory. This study provided an extended understanding of the role of systemic nitrogen reallocation for the interaction of tea plants and geometrids and the root-mediated resource-based resistance strategy employed by tea plants in response to leaf herbivory.
New insights into the regulation of plant immunity by amino acid metabolic pathways.
Plant, cell & environment
Besides defence pathways regulated by classical stress hormones, distinct amino acid metabolic pathways constitute integral parts of the plant immune system. Mutations in several genes involved in Asp-derived amino acid biosynthetic pathways can have profound impact on plant resistance to specific pathogen types. For instance, amino acid imbalances associated with homoserine or threonine accumulation elevate plant immunity to oomycete pathogens but not to pathogenic fungi or bacteria. The catabolism of Lys produces the immune signal pipecolic acid (Pip), a cyclic, non-protein amino acid. Pip amplifies plant defence responses and acts as a critical regulator of plant systemic acquired resistance, defence priming and local resistance to bacterial pathogens. Asp-derived pyridine nucleotides influence both pre- and post-invasion immunity, and the catabolism of branched chain amino acids appears to affect plant resistance to distinct pathogen classes by modulating crosstalk of salicylic acid- and jasmonic acid-regulated defence pathways. It also emerges that, besides polyamine oxidation and NADPH oxidase, Pro metabolism is involved in the oxidative burst and the hypersensitive response associated with avirulent pathogen recognition. Moreover, the acylation of amino acids can control plant resistance to pathogens and pests by the formation of protective plant metabolites or by the modulation of plant hormone activity.
Principal transcriptional regulation and genome-wide system interactions of the Asp-family and aromatic amino acid networks of amino acid metabolism in plants.
Less Hadar,Angelovici Ruthie,Tzin Vered,Galili Gad
Amino acid metabolism is among the most important and best recognized networks within biological systems. In plants, amino acids serve multiple functions associated with growth. Besides their function in protein synthesis, the amino acids are also catabolized into energy-associated metabolites as well we into numerous secondary metabolites, which are essential for plant growth and response to various stresses. Despite the central importance of amino acids in plants growth, elucidation of the regulation of amino acid metabolism within the context of the entire system, particularly transcriptional regulation, is still in its infancy. The different amino acids are synthesized by a number of distinct metabolic networks, which are expected to possess regulatory cross interactions between them for proper coordination of their interactive functions, such as incorporation into proteins. Yet, individual amino acid metabolic networks are also expected to differentially cross interact with various genome-wide gene expression programs and metabolic networks, in respect to their functions as precursors for various metabolites with distinct functions. In the present review, we discuss our recent genomics, metabolic and bioinformatics studies, which were aimed at addressing these questions, focusing mainly on the Asp-family metabolic network as the main example and also comparing it to the aromatic amino acids metabolic network as a second example (Angelovici et al. in Plant Physiol 151:2058-2072, 2009; Less and Galili in BMC Syst Biol 3:14, 2009; Tzin et al. in Plant J 60:156-167, 2009). Our focus on these two networks is because of the followings: (i) both networks are central to plant metabolism and growth and are also precursors for a wide range of primary and secondary metabolites that are indispensable to plant growth; (ii) the amino acids produced by these two networks are also essential to the nutrition and health of human and farm animals; and (iii) both networks contain branched pathways requiring extensive regulation of fluxes between the different branches. Additional views on the biochemistry, regulation and functional significance of the Asp-family and aromatic amino acid networks and some of their associated metabolites that are discussed in the present report, as well as the nutritional importance of Lys and Trp to human and farm animals, and attempts to improve Lys level in crop plants, can be obtained from the following reviews as examples (Radwanski and Last in Plant Cell 7:921-934, 1995; Halkier and Gershenzon in Annu Rev Plant Biol 57:303-333, 2006; Ufaz and Galili in Plant Physiol 147:954-961, 2008; Jander and Joshi in Mol Plant 3:54-65, 2010).