Both Allene Oxide Synthases Genes Are Involved in the Biosynthesis of Herbivore-Induced Jasmonic Acid and Herbivore Resistance in Rice.

Allene oxide synthase (AOS) is the second enzyme in the biosynthesis of the plant defensive hormone jasmonic acid (JA). In rice, there are two AOSs, OsAOS1 and OsAOS2. However, the role of these two AOS genes in herbivore-induced defenses in rice remains unidentified. We cloned the two rice AOS genes and observed that the transcript level of both and was enhanced by mechanical wounding, the infestation of the striped stem borer (SSB) () or brown planthopper (BPH) (), and treatment with JA; however, responded more rapidly to SSB infestation and JA treatment than did . The antisense expression of (as-) or (as-) decreased levels of SSB- or BPH-induced JA, which, in turn, reduced the production of SSB-induced trypsin protease inhibitor (TrypPI) and volatiles as well as the resistance of rice to SSB. In contrast, BPH preferred to feed and oviposit on wild-type (WT) plants over as- and as- plants. Moreover, the survival of BPH nymphs on as- or as- lines was significantly lower than on WT plants. The increased resistance of as- or as- plants to BPH correlated with higher levels of BPH-induced HO and SA. These results indicate that and are both involved in herbivore-induced JA biosynthesis and play a vital role in determining the resistance of rice to chewing and phloem-feeding herbivores.