Antagonistic Effects of Jasmonic Acid and Ethylene on Rubber Biosynthesis in Hevea brasiliensis
Based on the fact that ethephon(an ethylene releaser)stimulation can significantly increase latex yield per tapping,it is traditionally believed that rubber biosynthesis is positively regulated by ethylene.Based on the critical role of jasmonic acid signaling in promoting the biosynthesis of secondary metabolites in plants,jasmonic acid signaling is also thought to play a role in the positive feedback regulation of natural rubber biosynthesis.Recent studies suggest that tapping-enhanced rubber biosynthesis is closely related to the activation of jasmonate signaling in laticifer cells of rub-ber tree.However,it remains unclear whether there is a crosstalk between the jasmonic acid signaling pathway and the ethylene signaling pathway in the regulation of rubber biosynthesis.For this purpose,in the present study,in vitro rub-ber biosynthesis efficiency of whole latex and small rubber particles(SRPs)from short rested trees treated by either methy jasmonates or ethylene were detected by using substrate 13C-MVA.qPCR was used to analyze the expression of four jasmonic acid signaling genes,HbCOI1,HbJ AZ1,HbMYC1,HbMYC2,four ethylene-responsive element binding factors(ERFs)genes HbERFⅢa,HbERFⅦa,HbERFⅨc,HbERFⅩa,four rubber biosynthesis genes,HbHMGR1,HbSRPP1,HbREF1,HbHRT2 in laticifer cells after epicormic shoots were treated with either methy jasmonates or eth-ylene.The results showed that exogenous methyl jasmonate treatment significantly up-regulated the expression levels of jasmonic acid signaling genes HbCOI1,HbJ AZ1,HbMYC1,HbMYC2,and rubber biosynthetic protein genes HbHMGR1,HbSRPP1,HbREF1,HbHRT2 in laticifer cells of rubber tree,and promoted rubber biosynthesis,but had little effect on the expression of ethylene-responsive element binding factor genes HbERFⅢa,HbERFⅦa,HbERFⅨc,HbERFⅩa,or even inhibited the expression.On the contrary,exogenous ethylene treatment significantly up-regulated the expression levels of ethylene-responsive element binding factor genes HbERFⅢa,HbERFⅦa,HbERFⅨc,HbERFⅩa in laticifer cells of rubber tree,but had little effect on the expression of jasmonic acid signaling genes HbCOI1,HbJ AZ1,HbMYC1,HbMYC2 and rubber biosynthetic protein genes HbHMGR1,HbSRPP1,HbREF1,HbHRT2 or even inhibited the ex-pression and rubber biosynthesis.The results suggest that there exists an antagonistic effects of jasmonic acid and eth-ylene on rubber biosynthesis in H.brasiliensis,which would provide a theoretical basis for elucidating the crosstalk of jasmonic acid signaling and ethylene signaling on regulation of natural rubber production.
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