An ETHYLENE RESPONSE FACTOR-MYB Transcription Complex Regulates Furaneol Biosynthesis by Activating <i>QUINONE OXIDOREDUCTASE</i> Expression in Strawberry

Abstract

4-Hydroxy-2,5-dimethyl-3(2H)-furanone is a major contributor to the aroma of strawberry (<i>Fragaria</i> × <i>ananassa</i>) fruit, and the last step in its biosynthesis is catalyzed by strawberry quinone oxidoreductase (FaQR). Here, an ethylene response factor (FaERF#9) was characterized as a positive regulator of the <i>FaQR</i> promoter. Linear regression analysis indicated that <i>FaERF#9</i> transcript levels were correlated significantly with both <i>FaQR</i> transcripts and furanone content in different strawberry cultivars. Transient overexpression of <i>FaERF#9</i> in strawberry fruit significantly increased <i>FaQR</i> expression and furaneol production. Yeast one-hybrid assays, however, indicated that FaERF#9 by itself did not bind to the <i>FaQR</i> promoter. An MYB transcription factor (FaMYB98) identified in yeast one-hybrid screening of the strawberry cDNA library was capable of both binding to the promoter and activating the transcription of <i>FaQR</i> by ∼5.6-fold. Yeast two-hybrid assay and bimolecular fluorescence complementation confirmed a direct protein-protein interaction between FaERF#9 and FaMYB98, and in combination, they activated the <i>FaQR</i> promoter 14-fold in transactivation assays. These results indicate that an ERF-MYB complex containing FaERF#9 and FaMYB98 activates the <i>FaQR</i> promoter and up-regulates 4-hydroxy-2,5-dimethyl-3(2H)-furanone biosynthesis in strawberry.