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.
Ru-Feng Song,Lin Li,Xin-Ru Guo,Cai-Yi Liao,Wen-Cheng Liu
H 2 O 2 functions as a signaling molecule regulating plant growth, development, and stress responses; however, its role in jasmonic acid (JA) signaling transduction and JA-regulated biological processes remains elusive. Here, we report that General regulatory factor 8 (GRF8) is a critical factor inhibiting JA signaling, while H 2 O 2 removes this inhibition to facilitate the JA response during root growth and leaf senescence in Arabidopsis . GRF8 interacts with and inhibits MYC2, the key transcription factor in JA signaling. It recruits Jasmonate-ZIM domain (JAZ) repressors to enhance their interaction with and inhibition of MYC2. Additionally, GRF8 competes with Mediator 25 (MED25), a subunit of the Mediator coactivator complex, to interact with MYC2. Upon increased JA levels, H 2 O 2 sulfenylates GRF8 at cysteine-103, reducing its interaction with MYC2 and thereby releasing MYC2 activity to stimulate the JA response. Together, our findings suggest that H 2 O 2 -mediated sulfenylation of GRF8 provides a redox-based mechanism to modulate JA signaling in Arabidopsis .
Min Shi,Yao Wang,Xiaorong Wang,Changping Deng,Wenzhi Cao,Qiang Hua,Guoyin Kai
Tanshinones and phenolic acids are two major groups of natural bioactive compounds in Salvia miltiorrhiza which exert excellent pharmacological activities. Due to low content in S.miltiorrhiza , it is urgent to enhance the production of the two compounds to meet the increasing need. The Arabidopsis basic helix-loop-helix (bHLH) transcription factor MYC2 was introduced into S. miltiorrhiza hairy roots. In the best transgenic line AtMYC2-3 , tanshinone yield was 14.06 mg/g dw which was increased by 5.45-fold more than that in the control line, while phenolic acid production was enhanced to 95.9 mg/g dw, a 3.3-fold increase compared with the control. Transcript levels of some genes involved in biosynthesis of tanshinones and phenolic acids were noticeably upregulated. Dual-luciferase assay revealed that AtMYC2 activated the expression of biosynthetic genes including SmDXS2 and SmTAT . These results revealed that AtMYC2 plays a positive role in accumulation of both tanshinones and phenolic acids which provides a promising strategy for engineering tanshinone and phenolic acid production in S. miltiorrhiza .
In this study, we used virus-mediated gene silencing technology and found that the HSP17.4 gene-silenced cultivar Sweet Charlie plants were more susceptible to Colletotrichum gloeosporioides than the wild-type Sweet Charlie, and the level of infection was even higher than that of the susceptible cultivar Benihopp. The results of differential quantitative proteomics showed that after infection with the pathogen, the expression of the downstream response genes NPR1 , TGA , and PR-1 of the salicylic acid (SA) signalling pathway was fully up-regulated in the wild-type Sweet Charlie, and the expression of the core transcription factor MYC2 of the jasmonic acid (JA) pathway was significantly down-regulated. The expression of the proteins encoded by these genes did not change significantly in the HSP17.4 -silenced Sweet Charlie, indicating that the expression of HSP17.4 activated the up-regulation of downstream signals of SA and inhibited the JA signal pathway. The experiments that used SA, methyl jasmonate, and their inhibitors to treat plants provide additional evidence that the antagonism between SA and JA regulates the resistance of strawberry plants to C . gloeosporioides .
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