Molecular Biology, Enzymology, and Physiology of β-Oxidation

Hooks, Mark A.

doi:10.1007/978-94-015-9858-3_2

Cited by 20 publications

(18 citation statements)

References 129 publications

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“…Regardless of the exact substrate imported into the peroxisome there is considerable evidence for strong coordination of metabolism between peroxisomal and mitochondrial processes that extends beyond their combined operation in pathways, such as photorespiration, which are shared between multiple organelles. The results we present here concerning plants deficient in mitochondrial citrate synthase are consistent with those of other laboratories in demonstrating a clear role for the peroxisomal production of citrate, in conjuncture with the operation of the mitochondrial TCA cycle, in respiration of acetyl units from peroxisomal b-oxidation of fatty acids (Raymond et al, 1992;Hooks, 2002;Pracharoenwattana et al, 2005). They also help to explain previous observations that peroxisomal citrate synthase activity is detected in a wide range of tissues and not only those in which the glyoxylate cycle is active (Cornah and Smith, 2002;Pracharoenwattana et al, 2005).…”

Section: Discussionsupporting

confidence: 92%

Mild Reductions in Mitochondrial Citrate Synthase Activity Result in a Compromised Nitrate Assimilation and Reduced Leaf Pigmentation But Have No Effect on Photosynthetic Performance or Growth

Sienkiewicz‐Porzucek¹,

Nunes‐Nesi²,

Sulpice³

et al. 2008

Plant Physiology

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Transgenic tomato (Solanum lycopersicum) plants, expressing a fragment of the mitochondrial citrate synthase gene in the antisense orientation and exhibiting mild reductions in the total cellular activity of this enzyme, displayed essentially no visible phenotypic alteration from the wild type. A more detailed physiological characterization, however, revealed that although these plants were characterized by relatively few changes in photosynthetic parameters they displayed a decreased relative flux through the tricarboxylic acid cycle and an increased rate of respiration. Furthermore, biochemical analyses revealed that the transformants exhibited considerably altered metabolism, being characterized by slight decreases in the levels of organic acids of the tricarboxylic acid cycle, photosynthetic pigments, and in a single line in protein content but increases in the levels of nitrate, several amino acids, and starch. We additionally determined the maximal catalytic activities of a wide range of enzymes of primary metabolism, performed targeted quantitative PCR analysis on all three isoforms of citrate synthase, and conducted a broader transcript profiling using the TOM1 microarray. Results from these studies confirmed that if the lines were somewhat impaired in nitrate assimilation, they were not severely affected by this, suggesting the presence of strategies by which metabolism is reprogrammed to compensate for this deficiency. The results are discussed in the context of carbonnitrogen interaction and interorganellar coordination of metabolism.

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Section: Discussionsupporting

confidence: 92%

Mild Reductions in Mitochondrial Citrate Synthase Activity Result in a Compromised Nitrate Assimilation and Reduced Leaf Pigmentation But Have No Effect on Photosynthetic Performance or Growth

Sienkiewicz‐Porzucek¹,

Nunes‐Nesi²,

Sulpice³

et al. 2008

Plant Physiology

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“…The proposed requirement for peroxisomal CSY in fatty acid b-oxidation is consistent with the observed expression throughout the plant of CSY genes ( Figure 2B) and b-oxidation genes (Hooks, 2002). Peroxisomal CSY activity is detected in a range of plant tissues, rather than just those in which the glyoxylate cycle is active (Cornah and Smith, 2002).…”

Section: Discussionsupporting

confidence: 83%

“…This is explained by the expression of CSY1 only in siliques and specifically in developing seeds (Figure 2B,top and middle panels). Several studies have shown b-oxidation activity in developing oilseeds (Eccleston and Ohlrogge, 1998;Hooks, 2002) and the acx3 acx4 double mutant has an embryo-lethal phenotype, showing the importance of b-oxidation in seed development (Rylott et al, 2003). We propose that the requirement for peroxisomal CSY in fatty acid b-oxidation during seed development is fulfilled by the CSY1 isoform in csy2 csy3 double mutants.…”

Section: Discussionmentioning

confidence: 72%

“…No b-oxidation mutants so far described are compromised to such an extent as csy2 csy3, but in all cases this can be explained by redundancy of genes (Richmond and Bleecker, 1999;Germain et al, 2001;Hooks, 2002;Fulda et al, 2004). An alternative explanation is that CoA is sequestered as acetyl-CoA in the csy2 csy3 mutant and that either the lack of free CoA or an inhibitory effect of acetyl-CoA may inhibit growth.…”

Section: Discussionmentioning

confidence: 96%

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Arabidopsis Peroxisomal Citrate Synthase Is Required for Fatty Acid Respiration and Seed Germination

2005

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We tested the hypothesis that peroxisomal citrate synthase (CSY) is required for carbon transfer from peroxisomes to mitochondria during respiration of triacylglycerol in Arabidopsis thaliana seedlings. Two genes encoding peroxisomal CSY are expressed in Arabidopsis seedlings, and seeds from plants with both CSY genes disrupted were dormant and did not metabolize triacylglycerol. Germination was achieved by removing the seed coat and supplying sucrose, but the seedlings still did not use triacylglycerol. The mutant seedlings were resistant to 2,4-dichlorophenoxybutyric acid, indicating a block in peroxisomal b-oxidation, and were unable to develop further after transfer to soil. The mutant phenotype was complemented with a cDNA encoding CSY with either its native peroxisomal targeting sequence (PTS2) or a heterologous PTS1 sequence from pumpkin (Cucurbita pepo) malate synthase. These results suggest that peroxisomal CSY in Arabidopsis is not only a key enzyme of the glyoxylate cycle but also catalyzes an essential step in the respiration of fatty acids. We conclude that citrate is exported from the peroxisome during fatty acid respiration, whereas in yeast, acetylcarnitine is exported.

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“…Aunque los procesos de β-oxidación se han descrito principalmente asociados a tejidos de reserva como semillas, esta ruta es activa a lo largo del ciclo biológico de las plantas, y es operativa en una gran variedad de órganos que incluyen hojas jóvenes, hojas senescentes, inflorescencias y zonas meristemáticas de las raíces (Hooks, 2002;Charlton et al, 2005a;Goefert y Poirier, 2007). El análisis de expresión de los genes KAT mostró un patrón de acumulación específico del tejido y momento del desarrollo analizado.…”

Section: Arabidopsisunclassified

Función del gen 3-cetoacil-CoA tiolasa 2 (KAT2) en defensa y desarrollo. Participación de los peroxisomas en las respuestas a herida en Arabidopsis thaliana.

Toro¹,

Cruz²

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A mis padres A Andrés RESUMEN La β-oxidación es un proceso metabólico esencial en las células eucarióticas.Tradicionalmente, esta ruta catabólica ha sido considerada en plantas como la vía principal de degradación de ácidos grasos en las células. Sin embargo, en los últimos años, la β-oxidación de plantas está siendo objeto de un gran interés científico por su implicación en funciones relacionadas con el desarrollo y la defensa. En este contexto, aunque en estudios bioquímicos previos se había propuesto la participación de reacciones de β-oxidación en la biosíntesis de ácido salicílico (SA) y ácido jasmónico (JA), moléculas señalizadoras clave en las respuestas de defensa de plantas frente a patógenos y herida, no se había descrito la implicación de ningún enzima de β-oxidación hasta la realización de este trabajo. De todos los pasos enzimáticos implicados en esta ruta, la familia de las 3-cetoacil-CoA tiolasas (KAT) son las enzimas y genes menos estudiados. Este trabajo se ha centrado en la caracterización molecular y funcional de los distintos genes que codifican proteínas KAT de Arabidopsis, principalmente del gen KAT2 que codifica la proteína con la función KAT mayoritaria en β-oxidación en Arabidopsis. Para determinar las posibles funciones del gen KAT2 en procesos relacionados con el desarrollo y con la defensa de las plantas, se generaron plantas transgénicas con pérdida o ganancia de función del gen y otras donde la secuencia promotora de KAT2 se fusionó a genes delatores, las cuales permitieron caracterizar en mayor profundidad el patrón de expresión de este gen en Arabidopsis. Los análisis de expresión realizados demostraron que la herida activa transcripcionalmente genes de β-oxidación con un patrón de inducción específico. Concretamente, el gen KAT2 aumentó su expresión a través de una vía de señalización independiente de la señalización mediada por JA y posiblemente dependiente de ácido abcísico. Además, plantas transgénicas con una expresión reducida del gen KAT2 mostraron en respuesta a la herida una disminución severa en la acumulación de JA, indicando que KAT2 interviene en la biosíntesis de JA en respuesta a herida y posiblemente en otras respuestas de defensa dependientes de esta hormona. Este resultado constituye la primera evidencia de la implicación de un enzima de β-oxidación en la biosíntesis de JA en plantas. Por el contrario, frente a patógenos biotrofos como Pseudomonas syringae o a luz ultravioleta C, cuya defensa depende mayoritariamente de la síntesis y señalización de SA en la planta, el análisis de genes marcadores permitió comprobar que KAT2 no interviene en la síntesis de esta hormona. Por tanto, la ruta de biosíntesis de SA dependiente de reacciones de β-oxidación, descrita previamente en solanáceas, no está activa en respuesta a estrés en Arabidopsis. Además de las respuestas a estrés, se analizó la función del gen KAT2 en procesos del desarrollo como la germinación, el establecimiento postgerminativo y en procesos de senescencia. Estos análisis demostraron que KAT2 es necesar...

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Molecular Biology, Enzymology, and Physiology of β-Oxidation

Cited by 20 publications

References 129 publications

Mild Reductions in Mitochondrial Citrate Synthase Activity Result in a Compromised Nitrate Assimilation and Reduced Leaf Pigmentation But Have No Effect on Photosynthetic Performance or Growth

Mild Reductions in Mitochondrial Citrate Synthase Activity Result in a Compromised Nitrate Assimilation and Reduced Leaf Pigmentation But Have No Effect on Photosynthetic Performance or Growth

Arabidopsis Peroxisomal Citrate Synthase Is Required for Fatty Acid Respiration and Seed Germination

Función del gen 3-cetoacil-CoA tiolasa 2 (KAT2) en defensa y desarrollo. Participación de los peroxisomas en las respuestas a herida en Arabidopsis thaliana.

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