Ethylene Response Factors regulate expression of HbSUT3, the sucrose influx carrier in laticifers of Hevea brasiliensis.

Natural rubber is an important industrial raw material and commercially produced by rubber tree (Hevea brasiliensis). The sucrose transporter HbSUT3 plays an essential role in rubber production. Its expression in latex (cytoplasm of rubber-producing laticifers) is induced by bark treatment with Ethrel, an ethylene releaser, and the inducing effect correlates well with Ethrel-stimulated rubber yield increase. However, the mechanisms of ethylene induction on HbSUT3 expression are not known. Here, five Ethylene Response Factor (ERF) genes were identified from the cDNA library of Hevea latex by yeast one-hybrid screening with the promoter of HbSUT3 gene as bait. As revealed in a tobacco protoplast transient expression system, these HbERFs were mainly localized in the nucleus and four of them exhibited apparent transactivation activity. Of the five HbERF genes, HbERF-IXc4 was the most frequently screened in yeast one-hybrid, accounting for 65% of the ERF clones obtained. Moreover, among the five HbERFs, HbERF-IXc4 showed the strongest transactivation capacity when expressed in tobacco protoplast, the highest transcript abundance in latex, and a close expressional correlation with its target gene, HbSUT3, in response to the Ethrel treatment. Taken together, our results indicate that ERFs, especially HbERF-IXc4 is critically involved in the activation of HbSUT3 expression in latex after the Ethrel treatment on Hevea bark, and thus the stimulated latex yield.