A nuclear gene encoding mitochondrial Δ¹‐pyrroline‐5‐carboxylate dehydrogenase and its potential role in protection from proline toxicity

Abstract

Summary Δ1‐pyrroline‐5‐carboxylate (P5C), an intermediate in biosynthesis and degradation of proline (Pro), is assumed to play a role in cell death in plants and animals. Toxicity of external Pro and P5C supply to Arabidopsis suggested that P5C dehydrogenase (P5CDH; EC 1.2.1.12) plays a crucial role in this process by degrading the toxic Pro catabolism intermediate P5C. Also in a Δput2 yeast mutant, lacking P5CDH, Pro led to growth inhibition and formation of reactive oxygen species (ROS). Complementation of the Δput2 mutant allowed identification of the Arabidopsis P5CDH gene. AtP5CDH is a single‐copy gene and the encoded protein was localized to the mitochondria. High homology of AtP5CDH to LuFIS1, an mRNA up‐regulated during susceptible pathogen attack in flax, suggested a role for P5CDH in inhibition of hypersensitive reactions. An Arabidopsis mutant (cpr5) displaying a constitutive pathogen response was found to be hypersensitive to external Pro. In agreement with a role in prevention of cell death, AtP5CDH was expressed at a basal level in all tissues analysed. The highest expression was found in flowers that are known to contain the highest Pro levels under normal conditions. External supply of Pro induced AtP5CDH expression, but much more slowly than Pro dehydrogenase (AtProDH) expression. Uncoupled induction of the AtProDH and AtP5CDH genes further supports the hypothesis that P5C levels have to be tightly controlled. These results indicate that, in addition to the well‐studied functions of Pro, for example in osmoregulation, the Pro metabolism intermediate P5C also serves as a regulator of cellular stress responses.

Significant improvement of stress tolerance in tobacco plants by overexpressing a stress-responsive aldehyde dehydrogenase gene from maize (Zea mays)

“…Reliable controls include observations in the wild type and YFP alone transgenic plants that argue against other possibilities of the predicted subcellular localizations. To our knowledge, characterized plant ALDHs have been demonstrated to be targeted to diverse compartments including mitochondria (Busch and Fromm 1999;Nakazono et al 2000;Deuschle et al 2001;Liu et al 2001;Skibbe et al 2002), plastid/chloroplast (Kirch et al 2001;Weigel et al 1986;Kotchoni et al 2006), Cytosol (Rumpho et al 1983Nair et al 2004;Kotchoni et al 2006), and peroxisome (Nakamura et al 1997). Although the biochemical function of the aldehyde dehydrogenase characterized here is not yet clear, physiological properties suggest a detoxification function in plastids.…”

“…Disrupted ALDH5F1 results in an enhanced sensitivity to both UV-B light and heat stress (Bouché et al 2003). Another mitochondrial D 1 -pyrroline-5-carboxylate dehydrogenase probably participated in preventing proline toxicity (Deuschle et al 2001). Two class-1/2 ALDH genes (ALDH2B7 and ALDH2C4) are also predicted to be localized in mitochondria and the enzymatic activity has been demonstrated for these enzymes (Skibbe et al 2002).…”

Molecular and Functional Analyses Support a Role of Ornithine-δ-Aminotransferase in the Provision of Glutamate for Glutamine Biosynthesis during Pine Germination

“…Orn-d-aminotransferase (d-OAT; EC 2.6.1.13) catalyzes the transamination of the d-amino group from Orn to 2-oxoglutarate, producing Glu 5-semialdehyde (GSA) and Glu. At physiological pH GSA is in spontaneous equilibrium with D 1 -pyrroline-5-carboxylate (P5C; Deuschle et al, 2001). GSA/P5C can also be synthesized from Glu by the reaction catalyzed by P5C synthetase (EC 2.7.2.11 and 1.2.1.41) involved in the Pro biosynthesis pathway.…”

“…GSA/P5C can also be synthesized from Glu by the reaction catalyzed by P5C synthetase (EC 2.7.2.11 and 1.2.1.41) involved in the Pro biosynthesis pathway. In fact, GSA/P5C are intermediates in both Pro synthesis and degradation (Deuschle et al, 2001). Pro is synthesized from P5C in the reaction catalyzed by the enzyme P5C reductase (EC 1.5.1.2), and catabolized by the sequential actions of two mitochondrial enzymes, Pro dehydrogenase (EC 1.5.99.8) that catalyzes the oxidation of Pro to P5C and P5C dehydrogenase (P5CDH; EC 1.5.1.12) that catalyzes the conversion of GSA to Glu (Deuschle et al, 2001).…”

Effect of pH on spectral characteristics of P5C-ninhydrin derivative: Application in the assay of ornithine amino transferase activity from tissue lysate

“…Further, P5C as an intermediate metabolite of proline metabolism is believed to play a role in cell death in animals and plants (9). In spite of the importance of P5C in overall intermediate metabolism, little is known about the circulatory / tissue level and urinary excretion of P5C.…”