Poster: Salinity
Abs #
105: Is Pyrroline-5-carboxylate (P5C), the proline cycle intermediate, a regulator of stress response in plants?
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Presenter: |
Miller, Gadi , mill@post.tau.ac.il |
Authors | Miller, Gadi (A) Honig, Arik (A) Stein, Hanan (A) Zilberstein, Aviah (A) | | Affiliations: |
(A): Dept. of Plant Sciences, Tel Aviv University, Tel Aviv, 69978, Israel
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Accumulation of free proline is a common denominator of diverse stresses in plants. P5C is the intermediate in both proline synthesis and degradation. Proline is synthesized in the cytosol from glutamate by the sequential action of P5CS and P5CR and oxidized in the mitochondria, by proline-dehydrogenase (PDh) and P5C-dehydrogenase (P5CDh).
In human cells, P5C acts as regulator of cellular redox-dependent pathways including p53-induce apoptosis. In plant cells, P5C increased the expression of several osmotically regulated genes in rice. Further more, treating Arabidopsis plants with P5C led to cell death symptoms.
To understand the P5C role in plant stress responses, plants with increased PDh expression or with inactivated P5CDh gene were analyzed. Transgenic tobacco plants over-expressing alfalfa PDh were generated, in an attempt to decrease proline and increase P5C levels during osmotic stress. Although a strong ectopic constitutive PDh expression was observed, there was no reduction in proline accumulation. Moreover, P5C was not accumulated in the PDh over-expressing plants under normal and stress conditions and its concentration remained relatively low as in wild type plants.
In the Arabidopsis p5cdh knockout mutant the increase in proline levels during salt stress was similar to that of WT plants. Whereas during recovery from stress, proline level in WT plants drastically decreased, while in the p5cdh mutant proline levels remained high. Conversely, P5C levels in WT and p5cdh mutant were similar.
Taken together our results indicate that an inner ÒfutileÓ cycle of P5CR and PDh eliminates P5C excess in the p5cdh and the PDh over expression mutants while maintaining high proline level during stress. This cycle may act as a cytosolic-mitochondrial energy shuttle.
