Responsive modes of Medicago sativa proline dehydrogenase genes during salt stress and recovery dictate free proline accumulation
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Free proline accumulation is an innate response of many plants to osmotic stress. To characterize transcriptional regulation of the key proline cycle enzymes in alfalfa (Medicago sativa), two proline dehydrogenase (MsPDH) genes and a partial sequence of Δ 1 -pyrroline-5-carboxylate dehydrogenase (MsP5CDH) gene were identified and cloned. The two MsPDH genes share a high nucleotide sequence homology and a similar exon/intron structure. Estimation of transcript levels during salt stress and recovery revealed that proline accumulation during stress was linearly correlated with a strong decline in MsPDH transcript levels, while Δ 1 -pyrroline-5-carboxylate synthetase (MsP5CS) and MsP5CDH steady-state transcript levels remained essentially unchanged. MsPDH transcript levels dramatically decreased in a fast, salt concentration-dependent manner. The extent of salt-induced proline accumulation also correlated with salt concentrations. Salt-induced repression of MsPDH1 promoter linked to the GUS reporter gene confirmed that the decline in MsPDH transcript levels was due to less transcription initiation. Contrary to the salt-dependent repression, a rapid induction of MsPDH transcription occurred at a very early stage of the recovery process, independently of earlier salt treatments. Hence our results suggest the existence of two different regulatory modes of MsPDH expression; the repressing mode that quantifies salt concentration in an as yet unknown mechanism and the ”rehydration”-enhancing mode that responds to stress relief in a maximal induction of MsPDH transcription. As yet the components of salt sensing as well as those that might interact with MsPDH promoter to reduce transcription are still unknown.
KeywordsMedicago sativa Proline Proline dehydrogenase P5C dehydrogenase Salt stress
Δ 1 -Pyrroline-5-carboxylate synthetase
Δ 1 -Pyrroline-5-carboxylate
We thank H. Eilenberg, Department of Plant Sciences, Tel Aviv University, for critically reading the manuscript. This study was supported by the European Commission Research grant (Contract OLK5-CT-2002-0084) and the Israeli Ministry of Agriculture, Chief Scientist grant (891-0155-01).
- Ginzberg I, Stein H, Kapulnik Y, Szabados L, Strizhov N, Schell J, Koncz C, Zilberstein A (1998) Isolation and characterization of two different cDNAs of delta-1-pyrroline-5-carboxylate synthase in alfalfa, transcriptionally induced upon salt stress. Plant Mol Biol 38:755–764PubMedCrossRefGoogle Scholar
- Nakashima K, Satoh R, Kiyosue T, Yamaguchi-Shinozaki K, Shinozaki K (1998) A gene encoding proline dehydrogenase is not only induced by proline and hypoosmolarity, but is also developmentally regulated in the reproductive organs of Arabidopsis. Plant Physiol 118:1233–1241PubMedCrossRefGoogle Scholar
- Oono Y, Seki M, Nanjo T, Narusaka M, Fujita M, Satoh R, Satou M, Sakurai T, Ishida J, Akiyama K, Iida K, Maruyama K, Satoh S, Yamaguchi-Shinozaki K, Shinozaki K (2003) Monitoring expression profiles of Arabidopsis gene expression during rehydration process after dehydration using ca 7000 full-length cDNA microarray. Plant J 34: 868–887PubMedCrossRefGoogle Scholar
- Strizhov N, Keller M, Mathur J, Koncz-Kalman Z, Bosch D, Prudovsky E, Schell J, Sneh B, Koncz C, Zilberstein A (1996) A synthetic cryIC gene, encoding a Bacillus thuringiensis delta-endotoxin, confers Spodoptera resistance in alfalfa and tobacco. Proc Natl Acad Sci USA 93:15012–15017PubMedCrossRefGoogle Scholar
- Strizhov N, Abraham E, Okresz L, Blickling S, Zilberstein A, Schell J, Koncz C, Szabados L (1997) Differential expression of two P5CS genes controlling proline accumulation during salt-stress requires ABA and is regulated by ABA1, ABI1 and AXR2 in Arabidopsis. Plant J 12:557–569PubMedCrossRefGoogle Scholar
- Yoshiba Y, Kiyosue T, Katagiri T, Ueda H, Mizoguchi T, Yamaguchishinozaki K, Wada K, Harada Y, Shinozaki, K (1995) Correlation between the induction of a gene for delta(1)-pyrroline-5-carboxylate synthetase and the accumulation of proline in Arabidopsis thaliana under osmotic stress. Plant J 7:751–760PubMedCrossRefGoogle Scholar