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 ca… Show more
“…Linkage analysis of the Arabidopsis Bay 3 Sha population yielded 12 intervals affecting one or more seed BCAA traits, of which three contained candidate BCAA catabolic enzymes and none contained BCAA biosynthetic enzymes (see Supplemental Data Set 3 online). Thus, GWAS results were also consistent with amino acid catabolism, rather than biosynthesis, playing a key role in determining free BCAA levels during seed maturation on a populationwide level (Zhu and Galili, 2003;Gu et al, 2010;Lu et al, 2011;Ding et al, 2012;Kirma et al, 2012).…”
Branched-chain amino acids (BCAAs) are three of the nine essential amino acids in human and animal diets and are important for numerous processes in development and growth. However, seed BCAA levels in major crops are insufficient to meet dietary requirements, making genetic improvement for increased and balanced seed BCAAs an important nutritional target. Addressing this issue requires a better understanding of the genetics underlying seed BCAA content and composition. Here, a genome-wide association study and haplotype analysis for seed BCAA traits in Arabidopsis thaliana revealed a strong association with a chromosomal interval containing two BRANCHED-CHAIN AMINO ACID TRANSFERASES, BCAT1 and BCAT2. Linkage analysis, reverse genetic approaches, and molecular complementation analysis demonstrated that allelic variation at BCAT2 is responsible for the natural variation of seed BCAAs in this interval. Complementation analysis of a bcat2 null mutant with two significantly different alleles from accessions Bayreuth-0 and Shahdara is consistent with BCAT2 contributing to natural variation in BCAA levels, glutamate recycling, and free amino acid homeostasis in seeds in an alleledependent manner. The seed-specific phenotype of bcat2 null alleles, its strong transcription induction during late seed development, and its subcellular localization to the mitochondria are consistent with a unique, catabolic role for BCAT2 in BCAA metabolism in seeds.
“…Linkage analysis of the Arabidopsis Bay 3 Sha population yielded 12 intervals affecting one or more seed BCAA traits, of which three contained candidate BCAA catabolic enzymes and none contained BCAA biosynthetic enzymes (see Supplemental Data Set 3 online). Thus, GWAS results were also consistent with amino acid catabolism, rather than biosynthesis, playing a key role in determining free BCAA levels during seed maturation on a populationwide level (Zhu and Galili, 2003;Gu et al, 2010;Lu et al, 2011;Ding et al, 2012;Kirma et al, 2012).…”
Branched-chain amino acids (BCAAs) are three of the nine essential amino acids in human and animal diets and are important for numerous processes in development and growth. However, seed BCAA levels in major crops are insufficient to meet dietary requirements, making genetic improvement for increased and balanced seed BCAAs an important nutritional target. Addressing this issue requires a better understanding of the genetics underlying seed BCAA content and composition. Here, a genome-wide association study and haplotype analysis for seed BCAA traits in Arabidopsis thaliana revealed a strong association with a chromosomal interval containing two BRANCHED-CHAIN AMINO ACID TRANSFERASES, BCAT1 and BCAT2. Linkage analysis, reverse genetic approaches, and molecular complementation analysis demonstrated that allelic variation at BCAT2 is responsible for the natural variation of seed BCAAs in this interval. Complementation analysis of a bcat2 null mutant with two significantly different alleles from accessions Bayreuth-0 and Shahdara is consistent with BCAT2 contributing to natural variation in BCAA levels, glutamate recycling, and free amino acid homeostasis in seeds in an alleledependent manner. The seed-specific phenotype of bcat2 null alleles, its strong transcription induction during late seed development, and its subcellular localization to the mitochondria are consistent with a unique, catabolic role for BCAT2 in BCAA metabolism in seeds.
“…Remarkably, the highly regulated production of 2-oxoglutarate by the action of the OGDH is involved in glucose oxidation through the TCA cycle occupying an amphibolic branch point in the cycle, where the energy-producing reaction of the 2-oxoglutarate degradation competes with glutamate synthesis through nitrogen incorporation into 2-oxoglutarate. As such, the importance of this step within the cycle is manifold: 1) OGDH is a key regulatory point allowing the flux of 2-oxoglutarate through TCA cycle (Zhang and Bryant 2011; Nunes-Nesi et al 2013), 2) the synthesis of the essential amino acid lysine through the α-aminoadipate pathway requires 2-oxoglutarate (Kirma et al 2012) and the synthesis of 2-oxoglutarate generates a branch linking this metabolite to other pathways such as amino acid biosynthesis (Araújo, Tohge, et al 2012), and finally 3) the 2-oxoglutarate seems to be a connection between classical and alternative pathways of respiration in feeding electrons to the mitochondrial electron transport chain (Araújo et al 2010). F ig .…”
The tricarboxylic acid (TCA) cycle, a crucial component of respiratory metabolism, is composed of a set of eight enzymes present in the mitochondrial matrix. However, most of the TCA cycle enzymes are encoded in the nucleus in higher eukaryotes. In addition, evidence has accumulated demonstrating that nuclear genes were acquired from the mitochondrial genome during the course of evolution. For this reason, we here analyzed the evolutionary history of all TCA cycle enzymes in attempt to better understand the origin of these nuclear-encoded proteins. Our results indicate that prior to endosymbiotic events the TCA cycle seemed to operate only as isolated steps in both the host (eubacterial cell) and mitochondria (alphaproteobacteria). The origin of isoforms present in different cell compartments might be associated either with gene-transfer events which did not result in proper targeting of the protein to mitochondrion or with duplication events. Further in silico analyses allow us to suggest new insights into the possible roles of TCA cycle enzymes in different tissues. Finally, we performed coexpression analysis using mitochondrial TCA cycle genes revealing close connections among these genes most likely related to the higher efficiency of oxidative phosphorylation in this specialized organelle. Moreover, these analyses allowed us to identify further candidate genes which might be used for metabolic engineering purposes given the importance of the TCA cycle during development and/or stress situations.
“…7). Asp is closely linked to several metabolites that play essential roles in primary metabolic pathways such as the tricarboxylic acid cycle that contributes to cellular energy metabolism (Kirma et al, 2012). It was possible that excess Asp could interrupt the energy production process and in turn decrease the energy in the plant cells available for the pathogen consumption.…”
Section: Role Of Atglr33 In Innate Immunity and Gsh-induced Defense mentioning
The tripeptide reduced glutathione (GSH; g-glutamate [Glu]-cysteine [Cys]-glycine) is a major endogenous antioxidant in both animal and plant cells. It also functions as a neurotransmitter mediating communication among neurons in the central nervous system of animals through modulating specific ionotropic Glu receptors (GLRs) in the membrane. Little is known about such signaling roles in plant cells. Here, we report that transient rises in cytosolic calcium triggered by exogenous GSH in Arabidopsis (Arabidopsis thaliana) leaves were sensitive to GLR antagonists and abolished in loss-of-function atglr3.3 mutants. Like the GSH biosynthesis-defective mutant PHYTOALEXIN DEFICIENT2, atglr3.3 showed enhanced susceptibility to the bacterial pathogen Pseudomonas syringae pv tomato DC3000. Pathogen-induced defense marker gene expression was also decreased in atglr3.3 mutants. Twenty-seven percent of genes that were rapidly responsive to GSH treatment of seedlings were defense genes, most of which were dependent on functional AtGLR3.3, while GSH suppressed pathogen propagation through the AtGLR3.3-dependent pathway. Eight previously identified putative AtGLR3.3 ligands, GSH, oxidized glutathione, alanine, asparagine, Cys, Glu, glycine, and serine, all elicited the AtGLR3.3-dependent cytosolic calcium transients, but only GSH and Cys induced the defense response, with the Gluinduced AtGLR3.3-dependent transcription response being much less apparent than that triggered by GSH. Together, these observations suggest that AtGLR3.3 is required for several signaling effects mediated by extracellular GSH, even though these effects may not be causally related.
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