Toxicity of free proline revealed in an Arabidopsis T-DNA-tagged mutant deficient in proline dehydrogenase

• Published in: Plant and cell physiology Vol. 44; no. 5; pp. 541 - 548
• Main Authors: Nanjo, T. (Institute of Physical and Chemical Research, Tsukuba, Ibaraki (Japan). Tsukuba Inst.), Fujita, M, Seki, M, Kato, T, Tabata, S, Shinozaki, K
• Format: Journal Article
• Language: English
• Published: Japan Oxford University Press 01.05.2003; Oxford Publishing Limited (England)
• Subjects: ARABIDOPSIS; Arabidopsis - drug effects; Arabidopsis - enzymology; Arabidopsis - genetics; DNA, Bacterial - genetics; Dose-Response Relationship, Drug; Gene Expression Regulation, Plant - drug effects; Keywords: cDNA microarray — Proline toxicity — Proline dehydrogenase — T-DNA-tagged mutant; MODE OF ACTION; MUTANTS; Mutation; Oligonucleotide Array Sequence Analysis; OXIDOREDUCTASES; P5C; P5C dehydrogenase; P5C synthase; P5CDH; P5CS; PHYTOTOXICITY; Plant Roots - drug effects; Plant Roots - genetics; Plant Roots - growth & development; Pro; ProDH/PDH; PROLINE; Proline - metabolism; Proline - toxicity; proline dehydrogenase; Proline Oxidase - genetics; Proline Oxidase - metabolism; RNA, Messenger - drug effects; RNA, Messenger - genetics; RNA, Messenger - metabolism; Δ1-pyrroline-5-carboxylate
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcg066

The toxicity of proline (Pro) to plant growth has raised questions despite its protective functions in response to environmental stresses. To evaluate Pro toxicity, we isolated an Arabidopsis T-DNA-tagged mutant, pdh, that had a defect in Pro dehydrogenase (AtProDH), which catalyzes the first step of Pro catabolism. The pdh mutant showed hypersensitivity to exogenous application of <= 10 mM L-Pro, at which wild-type plants grew normally. A dose-dependent increase in internal free Pro accumulation was observed in pdh plants during external Pro supply. These results do not just prove the toxicity of Pro, but also suggest that AtProDH is the only enzyme acting as a functional ProDH in Arabidopsis. To further analyze the targets of Pro toxicity, we compared the expression of thousands of genes by pdh plants with that by wild-type plants by cDNA microarray analysis. Most genes were unaffected. Here we demonstrate Pro toxicity by using the pdh mutant and discuss a cause-and-effect action between an excess of free Pro and growth inhibition in Arabidopsis.