Modulation of the Fragrance of Kam Sweet Rice by Jasmonic Acid and Abscisic Acid Might Involve the MYC2 and ABI5 Transcription Factors
Volatile compounds were analyzed using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O). Results showed that nonanal had the highest odor activity value in the filling grains. Nonanal was enhanced by application of JA and inhibited by ABA in the seedlings of Kam sweet rice. C9-aldehydes are significant odorants in many rice types and known products of the 9-lipoxygenase and 9-hydroperoxide lyases encoded by the OsLOX3 and OsHPL1 genes, respectively. OsLOX3 mRNA expression was higher in aromatic rice compared to a nonaromatic cultivar. mRNA expression of ABI5 and MYC2 negatively correlated with OsLOX3 expression ( r = −0.841, P < 0.01; and r = −0.512, P < 0.05). In conclusion, the transcription factors ABI5 and MYC2 might be involved in ABA and JA modulation of nonanal biosynthesis, which could be used to improve rice quality. Practical Applications Nonanal and 2-acetyl-1-pyrroline are important and potent flavor compounds in aromatic Kam sweet rice. The OsLOX3 gene was potentially identified as a critical gene in aromatic Kam sweet rice and the enhancing effect of JA on nonanal biosynthesis was confirmed. The transcription factors ABI5 and MYC2 seem to regulate the expression of the fragrance gene OsLOX3 while MYC2 act as a positive regulator involved in JA-mediated nonanal biosynthesis. ABI5 participate in the ABA signaling pathway to down-regulate the expression of OsLOX3. These results will help understand the pathways involved in the biosynthesis of rice fragrance, which could be used to improve the quality of rice.
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