An R2R3-MYB Transcription Factor Regulates Eugenol Production in Ripe Strawberry Fruit Receptacles

Abstract

Eugenol is a volatile phenylpropanoid that contributes to flower and ripe fruit scent. In ripe strawberry (Fragaria 3 ananassa) fruit receptacles, eugenol is biosynthesized by eugenol synthase (FaEGS2). However, the transcriptional regulation of this process is still unknown. We have identified and functionally characterized an R2R3 MYB transcription factor (EMISSION OF BENZENOID II [FaEOBII]) that seems to be the orthologous gene of PhEOBII from Petunia hybrida, which contributes to the regulation of eugenol biosynthesis in petals. The expression of FaEOBII was ripening related and fruit receptacle specific, although high expression values were also found in petals. This expression pattern of FaEOBII correlated with eugenol content in both fruit receptacle and petals. The expression of FaEOBII was repressed by auxins and activated by abscisic acid, in parallel to the ripening process. In ripe strawberry receptacles, where the expression of FaEOBII was silenced, the expression of CINNAMYL ALCOHOL DEHYDROGENASE1 and FaEGS2, two structural genes involved in eugenol production, was down-regulated. A subsequent decrease in eugenol content in ripe receptacles was also observed, confirming the involvement of FaEOBII in eugenol metabolism. Additionally, the expression of FaEOBII was under the control of FaMYB10, another R2R3 MYB transcription factor that regulates the early and late biosynthetic genes from the flavonoid/phenylpropanoid pathway. In parallel, the amount of eugenol in FaMYB10-silenced receptacles was also diminished. Taken together, these data indicate that FaEOBII plays a regulating role in the volatile phenylpropanoid pathway gene expression that gives rise to eugenol production in ripe strawberry receptacles.The octoploid cultivated strawberry (Fragaria 3 ananassa) is one of the most economically important, nonclimacteric, soft fruits, in which volatile compounds influence fruit flavor and aroma. Both characteristics contribute to the fruit organoleptic traits and are crucial factors to determine fruit quality.At present, extensive surveys on the components that contribute to strawberry flavor have been performed. In these studies, more than 360 volatiles have been identified (Latrasse, 1991;Nijssen, 1996;Zabetakis and Holden, 1997), but only 15 to 20 of them in wild varieties of strawberry are believed to be essential for sensory quality, together with nonvolatile sugars and organic acids (Schieberle and Hofmann, 1997). In contrast, in cultivated varieties of strawberry, only about six odor-active compounds have been identified as contributors to fruit flavor (Raab et al., 2006;Ulrich et al., 2007). Strawberry aroma is the result of the combined perception of fruity (ethyl butanoate, ethyl hexanoate, and methyl 2-methylbutanoat), green (Z-3-hexenal), sweaty (butanoic acid and 2-methylbutanoic acid), peach-like (g-decalactone), and caramel-like [4-hydroxy-2,5-dimethyl-3(2H)-furanone and 2,5-dimethyl-4-methoxy-3(2H)-furanone] flavor notes (Pyysalo et al., 1979;Larsen and Poll, 1992). Several wild strawb...

Identification and Transcript Analysis of the TCP Transcription Factors in the Diploid Woodland Strawberry Fragaria vesca

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