Poster: Hormones

Abs # 562: Jasmonic acid signaling in rice

Presenter:	Kim, Ju-Kon , jukon@bio.mju.ac.kr
Authors	Kim, Ju-Kon  (A)   Kim, Eun-Hye  (A)   Jung, Harin  (A)   Kim, Youn Shic  (A)   Song, Sang Ik  (A)   Nahm, Baek Hie  (A)   Choi, Yang Do  (B)
Affiliations:	(A): Biological Science, Myongji University (B): School of Agricultural Biotechnology

Jasmonic acid (JA), salicylic acid (SA), and ethylene signaling pathways are integrated in the regulation of stress response and plant development. JA and SA pathways are mutually antagonistic. It remains elusive, however, whether JA or its methyl ester, methyl jasmonate (MeJA) is the active molecule. The Arabidopsis JA carboxyl methyltransferase gene (AtJMT), which specifically converts JA to MeJA, was previously isolated and characterized. To study the function of MeJA as opposed to JA in monocot plants, AtJMT was linked to the maize Ubi1 promoter and transformed into rice. Expression of AtJMT in transgenic plants resulted in induction of a group of rice genes involving SalT, VSP and TLP. The same set of genes was also induced in leaf tissues of nontransgenic plants upon treatment with MeJA, but not with JA, suggesting that AtJMT produces MeJA, which activates the target genes. In addition, we have identified two rice salicylic acid methyltransferase genes OsSMT1 and 2 that are also activated by AtJMT overexpression in transgenic plants, indicating a role of MeJA in SA signaling. OsSMT1 encodes a carboxyl methyltransferase, which selectively methylates SA and BA (benzoate), producing MeSA and MeBA at similar efficiency, respectively, as revealed by GC-MS analysis using recombinant proteins. Ubi1::AtJMT plants grow and develop normally except that flower organs are severely altered. The numbers of carpel, anther, lodicule, lemma and palea were increased as compared to nontransgenic controls, exhibiting phenotypes reminiscent of CLAVATA1 mutants of Arabidopsis. Our results indicate that MeJA biosynthesis enhances MeSA production and also impairs with development of flower organs, in addition to stimulating its own signaling pathway.