Gad Galili

Publications (65)409.56 Total impact

• Article: Alteration of the interconversion of pyruvate and malate in the plastid or cytosol of ripening tomato fruit invoke diverse consequences on sugar, yet similar effects on cellular organic acid, metabolism and transitory starch accumulation.

  Sonia Osorio, Jose G Vallarino, Marek Szecowka, Shai Ufaz, Vered Tzin, Ruthie Angelovici, Gad Galili, Alisdair R Fernie
  [show abstract] [hide abstract]
  ABSTRACT: The aim of this work was to investigate the effect of decreased cytosolic phosphoenolpyruvate carboxykinase (PEPCK) and plastidic NADP-dependent malic enzyme (NADP-ME) on tomato (Solanum lycopersicum) ripening. Transgenic tomato plants with strongly reduced levels of PEPCK and plastidic NADP-ME were generated by RNA interference gene silencing under the control of a ripening-specific E8 promoter. While these genetic modifications had relatively little effect on the total fruit yield and size, they had strong effects in fruit metabolism. Both transformants were characterized by lower levels of starch at breaker stage. Analysis of the activation state of ADP-glucose pyrophosphorylase correlated with the decrease of starch in both transformats, which suggest that is due to an altered cellular redox status. Moreover, metabolic profiling and feeding experiments involving positional labelled glucoses of fruits lacking in plastidic NADP-malic enzyme and cytosolic PEPCK activities revealed differential changes in overall respiration rates and tricarboxylic acid (TCA) cycle flux. Inactivation of cytosolic PEPCK affected the respiration rate which suggests that excess of oxaloacetate OAA is converted to aspartate and reintroduced in the TCA via 2-oxoglutarate/glutamate. On the other hand, the plastidic NADP-malic enzyme antisense lines were characterized by no changes in respiration rates and TCA cycle flux and together with an increase of pyruvate kinase and phosphoenolpyruvate carboxylase activities indicates that pyruvate is supply through these enzymes to the TCA cycle. These results are discussed in the context of current models of the importance of malate during tomato fruit ripening.
  Plant physiology 12/2012; · 6.53 Impact Factor
• Article: Fortifying plants with the essential amino acids lysine and methionine to improve nutritional quality.

  Gad Galili, Rachel Amir
  [show abstract] [hide abstract]
  ABSTRACT: Humans, as well as farm animals, cannot synthesize a number of essential amino acids, which are critical for their survival. Hence, these organisms must obtain these essential amino acids from their diets. Cereal and legume crops, which represent the major food and feed sources for humans and livestock worldwide, possess limiting levels of some of these essential amino acids, particularly Lys and Met. Extensive efforts were made to fortify crop plants with these essential amino acids using traditional breeding and mutagenesis. However, aside from some results obtained with maize, none of these approaches was successful. Therefore, additional efforts using genetic engineering approaches concentrated on increasing the synthesis and reducing the catabolism of these essential amino acids and also on the expression of recombinant proteins enriched in them. In the present review, we discuss the basic biological aspects associated with the synthesis and accumulation of these amino acids in plants and also describe recent developments associated with the fortification of crop plants with essential amino acids by genetic engineering approaches.
  Plant Biotechnology Journal 11/2012; · 5.44 Impact Factor
• Article: ATI1, a newly identified atg8-interacting protein, binds two different Atg8 homologs.

  Tamar Avin-Wittenberg, Simon Michaeli, Arik Honig, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Autophagy is a mechanism used for the transport of macromolecules to the vacuole for degradation. It can be either non-selective or selective, resulting from the specific binding of target proteins to Atg8, an essential autophagy-related protein. Nine Atg8 homologs exist in the model plant Arabidopsis thaliana, suggesting possible different roles for different homologs. In a previous report published in the Plant Cell, our group identified two plant-specific proteins, termed ATI1 and ATI2, which bind Atg8f, as a representative of the nine Atg8 homologs. The proteins were shown to associate with novel starvation-induced bodies that move on the ER network and reach the lytic vacuole. Altered expression level of the proteins was also shown to affect the ability of seeds to germinate in the presence of the germination inhibiting hormone ABA. In the present addendum article, we demonstrate that, in addition to Atg8f, ATI1 binds Atg8h, an Atg8 homolog from a different sub-family, indicating that ATI1 is not a specific target of Atg8f.
  Plant signaling & behavior 06/2012; 7(6):685-7.
• Article: Selective autophagy in the aid of plant germination and response to nutrient starvation.

  Arik Honig, Tamar Avin-Wittenberg, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Selective autophagy, mediated by Atg8 binding proteins, has not been extensively studied in plants. Plants possess a large gene family encoding multiple isoforms of the Atg8 protein. We have recently reported the identification of two new, closely homologous Arabidopsis thaliana plant proteins that bind the Arabidopsis Atg8f protein isoform. These two proteins are specific to plants and have no homologs in nonplant organisms. The expression levels of the genes encoding these proteins are elevated during carbon starvation and also during late stages of seed development. Exposure of young seedlings to carbon starvation induces the production of a newly identified compartment decorated by these Atg8-binding proteins. This compartment dynamically moves along the endoplasmic reticulum membrane and is also finally transported into the vacuole. Enhanced or suppressed expression of these Atg8-binding proteins respectively enhances or suppresses seed germination under suboptimal germination conditions, indicating that they contribute to seed germination vigor.
  Autophagy 05/2012; 8(5):838-9. · 7.45 Impact Factor
• Article: The multifaceted role of aspartate-family amino acids in plant metabolism.

  Menny Kirma, Wagner L Araújo, Alisdair R Fernie, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Plants represent the major sources of human foods and livestock feeds, worldwide. However, the limited content of the essential amino acid lysine in cereal grains represents a major nutritional problem for human and for livestock feeding in developed countries. Optimizing the level of lysine in cereal grains requires extensive knowledge on the biological processes regulating the homeostasis of this essential amino acid as well as the biological consequences of this homeostasis. Manipulating biosynthetic and catabolic enzymes of lysine metabolism enabled an enhanced accumulation of this essential amino acid in seeds. However, this approach had a major effect on the levels of various metabolites of the tricarboxylic acid (TCA) cycle, revealing a strong interaction between lysine metabolism and cellular energy metabolism. Recent studies discussed here have shed new light on the metabolic processes responsible for the catabolism of lysine, as well as isoleucine, another amino acid of the aspartate-family pathway, into the TCA cycle. Here we discuss progress being made to understand biological processes associated with the catabolism of amino acids of the aspartate-family pathway and its importance for optimal improvement of the nutritional quality of plants.
  Journal of Experimental Botany 04/2012; 63(14):4995-5001. · 5.36 Impact Factor
• Source

  Available from: uky.edu

  Article: RNAi and microRNA: breakthrough technologies for the improvement of plant nutritional value and metabolic engineering

  Guiliang Tang, Gad Galili, Xun Zhuang
  [show abstract] [hide abstract]
  ABSTRACT: This article raises the complex issue of improving plant nutritional value through metabolic engineering and the potential of using RNAi and micro RNA technologies to overcome this complexity, focusing on a few key examples. It also highlights current knowledge of RNAi and microRNA functions and discusses recent progress in the development of new RNAi vectors and their applications. RNA interference (RNAi) and microRNA (miRNA) are recent breakthrough discoveries in the life sciences recognized by the 2006 Nobel Prize in Physiology or Medicine. The importance of these discoveries relates not only to elucidating the fundamental regulatory aspects of gene expression, but also to the tremendous potential of their applications in plants and animals. Here, we review recent applications of RNAi and microRNA for improving the nutritional value of plants, discuss applications of metabolomics technologies in genetic engineering, and provide an update on the related RNAi and microRNA technologies.
  Metabolomics 04/2012; 3(3):357-369. · 4.51 Impact Factor
• Article: Expression of a bacterial feedback-insensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase of the shikimate pathway in Arabidopsis elucidates potential metabolic bottlenecks between primary and secondary metabolism.

  Vered Tzin, Sergey Malitsky, Michal Moyal Ben Zvi, Mohamed Bedair, Lloyd Sumner, Asaph Aharoni, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: The shikimate pathway of plants mediates the conversion of primary carbon metabolites via chorismate into the three aromatic amino acids and to numerous secondary metabolites derived from them. However, the regulation of the shikimate pathway is still far from being understood. We hypothesized that 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) is a key enzyme regulating flux through the shikimate pathway. To test this hypothesis, we expressed a mutant bacterial AroG gene encoding a feedback-insensitive DAHPS in transgenic Arabidopsis plants. The plants were subjected to detailed analysis of primary metabolism, using GC-MS, as well as secondary metabolism, using LC-MS. Our results exposed a major effect of bacterial AroG expression on the levels of shikimate intermediate metabolites, phenylalanine, tryptophan and broad classes of secondary metabolite, such as phenylpropanoids, glucosinolates, auxin and other hormone conjugates. We propose that DAHPS is a key regulatory enzyme of the shikimate pathway. Moreover, our results shed light on additional potential metabolic bottlenecks bridging plant primary and secondary metabolism.
  New Phytologist 02/2012; 194(2):430-9. · 6.64 Impact Factor
• Article: Deciphering energy-associated gene networks operating in the response of Arabidopsis plants to stress and nutritional cues.

  Tamar Avin-Wittenberg, Vered Tzin, Ruthie Angelovici, Hadar Less, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Plants need to continuously adjust their transcriptome in response to various stresses that lead to inhibition of photosynthesis and the deprivation of cellular energy. This adjustment is triggered in part by a coordinated re-programming of the energy-associated transcriptome to slow down photosynthesis and activate other energy-promoting gene networks. Therefore, understanding the stress-related transcriptional networks of genes belonging to energy-associated pathways is of major importance for engineering stress tolerance. In a bioinformatics approach developed by our group, termed 'gene coordination', we previously divided genes encoding for enzymes and transcription factors in Arabidopsis thaliana into three clusters, displaying altered coordinated transcriptional behaviors in response to multiple biotic and abiotic stresses (Plant Cell, 23, 2011, 1264). Enrichment analysis indicated further that genes controlling energy-associated metabolism operate as a compound network in response to stress. In the present paper, we describe in detail the network association of genes belonging to six central energy-associated pathways in each of these three clusters described in our previous paper. Our results expose extensive stress-associated intra- and inter-pathway interactions between genes from these pathways, indicating that genes encoding proteins involved in energy-associated metabolism are expressed in a highly coordinated manner. We also provide examples showing that this approach can be further utilized to elucidate candidate genes for stress tolerance and functions of isozymes.
  The Plant Journal 01/2012; 70(6):954-66. · 6.16 Impact Factor
• Article: A new type of compartment, defined by plant-specific Atg8-interacting proteins, is induced upon exposure of Arabidopsis plants to carbon starvation.

  Arik Honig, Tamar Avin-Wittenberg, Shai Ufaz, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Atg8 is a central protein in bulk starvation-induced autophagy, but it is also specifically associated with multiple protein targets under various physiological conditions to regulate their selective turnover by the autophagy machinery. Here, we describe two new closely related Arabidopsis thaliana Atg8-interacting proteins (ATI1 and ATI2) that are unique to plants. We show that under favorable growth conditions, ATI1 and ATI2 are partially associated with the endoplasmic reticulum (ER) membrane network, whereas upon exposure to carbon starvation, they become mainly associated with newly identified spherical compartments that dynamically move along the ER network. These compartments are morphologically distinct from previously reported spindle-shaped ER bodies and, in contrast to them, do not contain ER-lumenal markers possessing a C-terminal HDEL sequence. Organelle and autophagosome-specific markers show that the bodies containing ATI1 are distinct from Golgi, mitochondria, peroxisomes, and classical autophagosomes. The final destination of the ATI1 bodies is the central vacuole, indicating that they may operate in selective turnover of specific proteins. ATI1 and ATI2 gene expression is elevated during late seed maturation and desiccation. We further demonstrate that ATI1 overexpression or suppression of both ATI1 and ATI2, respectively, stimulate or inhibit seed germination in the presence of the germination-inhibiting hormone abscisic acid.
  The Plant Cell 01/2012; 24(1):288-303. · 8.99 Impact Factor
• Article: Targeted enhancement of glutamate-to-γ-aminobutyrate conversion in Arabidopsis seeds affects carbon-nitrogen balance and storage reserves in a development-dependent manner.

  Aaron Fait, Adriano Nunes Nesi, Ruthie Angelovici, Martin Lehmann, Phuong Anh Pham, Luhua Song, Richard P Haslam, Johnathan A Napier, Gad Galili, Alisdair R Fernie
  [show abstract] [hide abstract]
  ABSTRACT: In seeds, glutamate decarboxylase (GAD) operates at the metabolic nexus between carbon and nitrogen metabolism by catalyzing the unidirectional decarboxylation of glutamate to form γ-aminobutyric acid (GABA). To elucidate the regulatory role of GAD in seed development, we generated Arabidopsis (Arabidopsis thaliana) transgenic plants expressing a truncated GAD from Petunia hybrida missing the carboxyl-terminal regulatory Ca(2+)-calmodulin-binding domain under the transcriptional regulation of the seed maturation-specific phaseolin promoter. Dry seeds of the transgenic plants accumulated considerable amounts of GABA, and during desiccation the content of several amino acids increased, although not glutamate or proline. Dry transgenic seeds had higher protein content than wild-type seeds but lower amounts of the intermediates of glycolysis, glycerol and malate. The total fatty acid content of the transgenic seeds was 50% lower than in the wild type, while acyl-coenzyme A accumulated in the transgenic seeds. Labeling experiments revealed altered levels of respiration in the transgenic seeds, and fractionation studies indicated reduced incorporation of label in the sugar and lipid fractions extracted from transgenic seeds. Comparative transcript profiling of the dry seeds supported the metabolic data. Cellular processes up-regulated at the transcript level included the tricarboxylic acid cycle, fatty acid elongation, the shikimate pathway, tryptophan metabolism, nitrogen-carbon remobilization, and programmed cell death. Genes involved in the regulation of germination were similarly up-regulated. Taken together, these results indicate that the GAD-mediated conversion of glutamate to GABA during seed development plays an important role in balancing carbon and nitrogen metabolism and in storage reserve accumulation.
  Plant physiology 09/2011; 157(3):1026-42. · 6.53 Impact Factor
• Article: A friend in need is a friend indeed: Understanding stress-associated transcriptional networks of plant metabolism using cliques of coordinately expressed genes.

  Tamar Avin-Wittenberg, Vered Tzin, Hadar Less, Ruthie Angelovici, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: The response of plants to environmental cues, particularly stresses, involves the coordinated induction or repression of gene expression. In a previous study, we developed a bioinformatics approach to analyze the mutual expression pattern of genes encoding transcription factors and metabolic enzymes upon exposure of Arabidopsis plants to abiotic and biotic stresses. The analysis resulted in three gene clusters, each displaying a unique expression pattern. In the present addendum, we address the composition of each of these three clusters in regard to the functional identity of their encoded proteins as enzymes or transcription factors.
  Plant signaling & behavior 09/2011; 6(9).
• Article: Variations on a theme: plant autophagy in comparison to yeast and mammals.

  Tamar Avin-Wittenberg, Arik Honig, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Autophagy is an evolutionary conserved process of bulk degradation and nutrient sequestration that occurs in all eukaryotic cells. Yet, in recent years, autophagy has also been shown to play a role in the specific degradation of individual proteins or protein aggregates as well as of damaged organelles. The process was initially discovered in yeast and has also been very well studied in mammals and, to a lesser extent, in plants. In this review, we summarize what is known regarding the various functions of autopahgy in plants but also attempt to address some specific issues concerning plant autophagy, such as the insufficient knowledge regarding autophagy in various plant species other than Arabidopsis, the fact that some genes belonging to the core autophagy machinery in various organisms are still missing in plants, the existence of autophagy multigene families in plants and the possible operation of selective autophagy in plants, a study that is still in its infancy. In addition, we point to plant-specific autophagy processes, such as the participation of autophagy during development and germination of the seed, a unique plant organ. Throughout this review, we demonstrate that the use of innovative bioinformatic resources, together with recent biological discoveries (such as the ATG8-interacting motif), should pave the way to a more comprehensive understanding of the multiple functions of plant autophagy.
  Protoplasma 06/2011; 249(2):285-99. · 1.92 Impact Factor
• Article: Coordinated gene networks regulating Arabidopsis plant metabolism in response to various stresses and nutritional cues.

  Hadar Less, Ruthie Angelovici, Vered Tzin, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: The expression pattern of any pair of genes may be negatively correlated, positively correlated, or not correlated at all in response to different stresses and even different progression stages of the stress. This makes it difficult to identify such relationships by classical statistical tools such as the Pearson correlation coefficient. Hence, dedicated bioinformatics approaches that are able to identify groups of cues in which there is a positive or negative expression correlation between pairs or groups of genes are called for. We herein introduce and discuss a bioinformatics approach, termed Gene Coordination, that is devoted to the identification of specific or multiple cues in which there is a positive or negative coordination between pairs of genes and can further incorporate additional coordinated genes to form large coordinated gene networks. We demonstrate the utility of this approach by providing a case study in which we were able to discover distinct expression behavior of the energy-associated gene network in response to distinct biotic and abiotic stresses. This bioinformatics approach is suitable to a broad range of studies that compare treatments versus controls, such as effects of various cues, or expression changes between a mutant and the control wild-type genotype.
  The Plant Cell 04/2011; 23(4):1264-71. · 8.99 Impact Factor
• Article: The aspartate-family pathway of plants: linking production of essential amino acids with energy and stress regulation.

  Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: The Asp family pathway of plants is highly important from a nutritional standpoint because it leads to the synthesis of the four essential amino acids Lys, Thr, Met and Ile. These amino acids are not synthesized by human and its monogastric livestock and should be supplemented in their diets. Among the Asp-family amino acids, Lys is considered as the nutritionally most important essential amino acid because its level is most limiting in cereal grains, representing the largest source of plant foods and feeds worldwide. Metabolic engineering approaches led to significant increase in Lys level in seeds by enhancing its synthesis and reducing its catabolism. However, results from the model plant Arabidopsis showed that this approach may retard seed germination due to a major negative effect on the levels of a number of TCA cycle metabolites that associate with cellular energy. In the present review, we discuss the regulatory metabolic link of the Asp-family pathway with the TCA cycle and its biological significance upon exposure to stress conditions that cause energy deprivation. In addition, we also discuss how deep understanding of the regulatory metabolic link of the Asp-family pathway with energy and stress regulation can be used to improve Lys level in seeds of important crop species, minimizing the interference with the cellular energy status and plant-stress interaction. This review thus provides an example showing how deep understanding the inter-regulation of metabolism with plant stress physiology can lead to successful nutritional improvements with minimal negative effect on plant growth and response to stressful environments.
  Plant signaling & behavior 02/2011; 6(2):192-5.
• Article: Metabolism: Amino acid regulatory wisdom.

  Tamar Avin-Wittenberg, Gad Galili
  Nature Chemical Biology 01/2011; 8(1):23-4. · 14.69 Impact Factor
• Article: Transcriptional control of aspartate kinase expression during darkness and sugar depletion in Arabidopsis: involvement of bZIP transcription factors.

  Shai Ufaz, Vijaya Shukla, Yulia Soloveichik, Yelena Golan, Frank Breuer, Zsuzsa Koncz, Gad Galili, Csaba Koncz, Aviah Zilberstein
  [show abstract] [hide abstract]
  ABSTRACT: Initial steps of aspartate-derived biosynthesis pathway (Asp pathway) producing Lys, Thr, Met and Ile are catalyzed by bifunctional (AK/HSD) and monofunctional (AK-lys) aspartate kinase (AK) enzymes. Here, we show that transcription of all AK genes is negatively regulated under darkness and low sugar conditions. By using yeast one-hybrid assays and complementary chromatin immunoprecipitation analyses in Arabidopsis cells, the bZIP transcription factors ABI5 and DPBF4 were identified, capable of interacting with the G-box-containing enhancer of AK/HSD1 promoter. Elevated transcript levels of DPBF4 and ABI5 under darkness and low sugar conditions coincide with the repression of AK gene expression. Overexpression of ABI5, but not DPBF4, further increases this AK transcription suppression. Concomitantly, it also increases the expression of asparagines synthetase 1 (ASN1) that shifts aspartate utilization towards asparagine formation. However, in abi5 or dpbf4 mutant and abi5, dpbf4 double mutant the repression of AK expression is maintained, indicating a functional redundancy with other bZIP-TFs. A dominant-negative version of DPBF4 fused to the SRDX repressor domain of SUPERMAN could counteract the repression and stimulate AK expression under low sugar and darkness in planta. This effect was verified by showing that DPBF4-SRDX fails to recognize the AK/HSD1 enhancer sequence in yeast one-hybrid assays, but increases heterodimmer formation with DPBF4 and ABI5, as estimated by yeast two-hybrid assays. Hence it is likely that heterodimerization with DPBF4-SRDX inhibits the binding of redundantly functioning bZIP-TFs to the promoters of AK genes and thereby releases the repressing effect. These data highlight a novel transcription control of the chloroplast aspartate pathway that operates under energy limiting conditions.
  Planta 01/2011; 233(5):1025-40. · 3.00 Impact Factor
• Source

  Available from: weizmann.ac.il

  Article: Metabolic engineering of the plant primary-secondary metabolism interface.

  Asaph Aharoni, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: Plants synthesize a myriad of secondary metabolites (SMs) that are derived from central or primary metabolism. While these so-called natural products have been targets for plant metabolic engineering attempts for many years, the immense value of manipulating the interface between committed steps in secondary metabolism pathways and those in primary metabolism pathways has only recently emerged. In this review we discuss a few of the major issues that should be taken into consideration in attempts to engineer the primary to secondary metabolism interface. The availability of carbon, nitrogen and sulfur resources will have a major impact on the production of specific classes of primary metabolites (PMs) and consequently on the levels and composition of SMs derived from these PMs. Recent studies have shown that transcription factors associated with the synthesis of a given class of SMs coactivate the expression of genes encoding metabolic enzymes associated with primary pathways that supply precursors to these SMs. In addition, metabolic engineering approaches, which alter post-transcriptional feedback and feedforward regulatory mechanisms of the primary-secondary metabolism interface, have been highly fruitful in Taylormade enhancements of the content of specific beneficial SMs. Lastly, the evolution of pathways of secondary metabolism from pathways of primary metabolism highlights the need to consider cases in which common enzymatic reactions and pathways take place between the two. Taken together, the available information indicates a supercoordinated gene expression networks connecting primary and secondary metabolism in plants, which should be taken into consideration in future attempts to metabolically engineer the various classes of plant SMs.
  Current opinion in biotechnology 12/2010; 22(2):239-44. · 7.82 Impact Factor
• Article: New insights into the shikimate and aromatic amino acids biosynthesis pathways in plants.

  Vered Tzin, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: The aromatic amino acids phenylalanine, tyrosine, and tryptophan in plants are not only essential components of protein synthesis, but also serve as precursors for a wide range of secondary metabolites that are important for plant growth as well as for human nutrition and health. The aromatic amino acids are synthesized via the shikimate pathway followed by the branched aromatic amino acids biosynthesis pathway, with chorismate serving as a major intermediate branch point metabolite. Yet, the regulation and coordination of synthesis of these amino acids are still far from being understood. Recent studies on these pathways identified a number of alternative cross-regulated biosynthesis routes with unique evolutionary origins. Although the major route of Phe and Tyr biosynthesis in plants occurs via the intermediate metabolite arogenate, recent studies suggest that plants can also synthesize phenylalanine via the intermediate metabolite phenylpyruvate (PPY), similarly to many microorganisms. Recent studies also identified a number of transcription factors regulating the expression of genes encoding enzymes of the shikimate and aromatic amino acids pathways as well as of multiple secondary metabolites derived from them in Arabidopsis and in other plant species.
  Molecular Plant 11/2010; 3(6):956-72. · 5.55 Impact Factor
• Article: A seed high-lysine trait is negatively associated with the TCA cycle and slows down Arabidopsis seed germination.

  Ruthie Angelovici, Aaron Fait, Alisdair R Fernie, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: • Lysine is a nutritionally important essential amino acid, but significant elevation of its levels in Arabidopsis seeds, by enhancing its synthesis and blocking its catabolism, causes a retardation of germination. Here, we hypothesized that this negative effect is associated with changes in primary metabolism and gene expression programs that are essential for early germination. • Seeds at different stages of germination sensu stricto of the seed-high-lysine genotype were subjected to detailed analysis of primary metabolism, using GC-MS, as well as microarray analysis and two-dimensional, isoelectric focusing, sodium dodecylsulfate polyacrylamide gel electrophoresis, to detect storage protein mobilization. • Our results exposed a major negative effect of the seed-specific increased lysine synthesis and knockout of its catabolism on the levels of a number of TCA cycle metabolites. This metabolic alteration also influences significantly the transcriptome, primarily attenuating the boost of specific transcriptional programs that are essential for seedling establishment, such as the onset of photosynthesis, as well as the turnover of specific transcriptional programs associated with seed embryonic traits. • Our results indicate that catabolism of the aspartic acid family of amino acids is an important contributor to the energy status of plants, and hence to the onset of autotrophic growth-associated processes during germination.
  New Phytologist 10/2010; 189(1):148-59. · 6.64 Impact Factor
• Article: Principal transcriptional regulation and genome-wide system interactions of the Asp-family and aromatic amino acid networks of amino acid metabolism in plants.

  Hadar Less, Ruthie Angelovici, Vered Tzin, Gad Galili
  [show abstract] [hide abstract]
  ABSTRACT: 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).
  Amino Acids 04/2010; 39(4):1023-8. · 3.25 Impact Factor