Botanical Institute, Molecular Cell Biology, Karlsruhe Institute of Technology, Kaiserstraße 2, 76131, Karlsruhe, Germany.
Plant J. 2013 Apr;74(2):226-38. doi: 10.1111/tpj.12115. Epub 2013 Mar 4.
Two photomorphogenic mutants of rice, coleoptile photomorphogenesis 2 (cpm2) and hebiba, were found to be defective in the gene encoding allene oxide cyclase (OsAOC) by map-based cloning and complementation assays. Examination of the enzymatic activity of recombinant GST-OsAOC indicated that OsAOC is a functional enzyme that is involved in the biosynthesis of jasmonic acid and related compounds. The level of jasmonate was extremely low in both mutants, in agreement with the fact that rice has only one gene encoding allene oxide cyclase. Several flower-related mutant phenotypes were observed, including morphological abnormalities of the flower and early flowering. We used these mutants to investigate the function of jasmonate in the defence response to the blast fungus Magnaporthe oryzae. Inoculation assays with fungal spores revealed that both mutants are more susceptible than wild-type to an incompatible strain of M. oryzae, in such a way that hyphal growth was enhanced in mutant tissues. The level of jasmonate isoleucine, a bioactive form of jasmonate, increased in response to blast infection. Furthermore, blast-induced accumulation of phytoalexins, especially that of the flavonoid sakuranetin, was found to be severely impaired in cpm2 and hebiba. Together, the present study demonstrates that, in rice, jasmonate mediates the defence response against blast fungus.
通过图谱定位克隆和互补测验，我们发现水稻的两个光形态建成突变体 coleoptile photomorphogenesis 2 (cpm2) 和 hebiba 均为编码丙二烯氧化物环化酶（OsAOC）的基因缺陷。重组 GST-OsAOC 的酶活性分析表明，OsAOC 是一种功能性酶，参与茉莉酸及其相关化合物的生物合成。两种突变体中的茉莉酸水平均极低，这与水稻只有一个编码丙二烯氧化物环化酶的基因的事实相符。观察到了几个与花相关的突变体表型，包括花的形态异常和早花。我们利用这些突变体研究茉莉酸在稻瘟病菌（Magnaporthe oryzae）防御反应中的功能。用真菌孢子进行接种试验表明，与野生型相比，这两个突变体对稻瘟病菌的一个非亲和菌株更敏感，以至于突变体组织中的菌丝生长增强。茉莉酸异亮氨酸（茉莉酸的一种生物活性形式）的水平在受到稻瘟病感染后增加。此外，还发现 cpm2 和 hebiba 中植物抗毒素，特别是类黄酮樱黄素的爆发诱导积累严重受损。总之，本研究表明，在水稻中，茉莉酸介导了对稻瘟病菌的防御反应。
