Jasmonic acid (JA) is involved in regulating the expression of certain plant defense genes and response to various stresses. JA biosynthesis is hypothesized to occur both in chloroplasts and the cytoplasm. In order to test whether or not a cytosol-localized allene oxide synthase (AOS) can promote JA biosynthesis, transgenic tobacco plants containing a flax AOS cDNA without a chloroplast transit sequence under the control of a tetracycline-inducible promoter were generated. Induction of the flax AOS gene in transgenic plants with chlor-tetracycline (Tc) led to the expression of the flax AOS mRNA and protein, which resulted in high level of metabolism of 13(S)-hydroperoxyoctadecatrienoic acid (13(S)-HPOT) and formation of 12-oxo-phytodienoic acid (12-O-PDA). Subcellular fractionation demonstrated that the flax AOS protein and activity were associated with the cytosol. Overexpression of the flax AOS in induced transgenic plants did not increase JA levels in healthy, undamaged leaf tissues. However, in wounded tissues overexpressing a flax AOS, levels of JA and the transcript of a pathogenesis-related gene (PR-1) dramatically increased when compared to those not expressing the flax AOS. Analysis of the release of wound-induced C6 volatiles showed that the level of (Z)-3-hexen-1-ol decreased about 30% due to overexpression of the cytoplasm-localized AOS, while (Z)-3-hexenal and (Z)-3-hexenyl acetate appeared not to be significantly altered. The data indicate that cytoplasmic AOS responds to wounding by increasing the levels of the wound-induced JA which in turn directly or indirectly enhances the expression of plant defense genes.
|Number of pages||11|
|Journal||Plant Molecular Biology|
|State||Published - Jul 1999|
Bibliographical noteFunding Information:
We would like to thank Dr A.R. Brash for the gifts of the AOS cDNA and antibody, Dr Christiane Gatz for the gifts of Tet-R+ tobacco seeds and pBIN-HYG-TX vector, Dr D. Klessig for the gift of PR-1 cDNA and Dr J.H. Loughrin for use of the volatile collection apparatus. We thank Dr H. Fukushige for his great help in GC and GC-MS analysis. We also thank Yuan Sun and Krista M. Hamilton for their excellent assistance. Work supported by THRI.
- Allene oxide synthase
- C volatiles
- Jasmonic acid
- Nicotina tabacum
- Pathogenesis-related gene
- Tretracycline-inducible promoter
ASJC Scopus subject areas
- Agronomy and Crop Science
- Plant Science