Up- and down-regulation of Fragariaxananassa O-methyltransferase: impacts on furanone and phenylpropanoid metabolism

Abstract

A complex mixture of hundreds of substances determines strawberry (Fragaria x ananassa) aroma, but only approximately 15 volatiles are considered as key flavour compounds. Of these, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) is regarded as the most important, but it is methylated further by FaOMT (Fragaria x ananassa O-methyltransferase) to 2,5-dimethyl-4-methoxy-3(2H)-furanone (DMMF) during the ripening process. It is shown here that transformation of strawberry with the FaOMT sequence in sense and antisense orientation, under the control of the cauliflower mosaic virus 35S promoter, resulted in a near total loss of DMMF, whereas the levels of the other volatiles remained unchanged. FaOMT repression also affected the ratio of feruloyl 1-O-beta-D-glucose and caffeoyl 1-O-beta-D-glucose, indicating a dual function of the enzyme in planta. Thus, FaOMT is involved in at least two different biochemical pathways in ripe strawberry fruit.

Genetic Analysis of Strawberry Fruit Aroma and Identification ofO-Methyltransferase FaOMTas the Locus Controlling Natural Variation in Mesifurane Content

“…FaOMT expression increased during ripening in the receptacle tissue while in the achene, the highest expression was observed in green fruit, decreasing later during ripening. This expression pattern is consistent with the role of FaOMT in the biosynthesis of mesifurane in the receptacle but also with the additional role that has been proposed in lignin biosynthesis (Lunkenbein et al, 2006b), which might be more relevant in the achene. The relative content of 87 volatiles identified by GC and MS was analyzed in the parental lines and F1 progeny over four successive years.…”

“…The substrate specificity of FaOMT indicates that it is involved in the methylation of furaneol to mesifurane (Wein et al, 2002). Furthermore, the inhibition of FaOMT in transgenic strawberry plants resulted in a near total loss of mesifurane (Lunkenbein et al, 2006b). This data together with the dramatic reduction of FaOMT expression in lines with trace content of mesifurane provide strong evidence indicating that FaOMT is the locus controlling mesifurane content in strawberry fruit and is responsible for its natural variation.…”

“…The strawberry protein O-methyltransferase (FaOMT) controls variation in mesifurane content via the methylation of furaneol using S-adenosyl-L-Met as methyl donor (Wein et al, 2002;Lunkenbein et al, 2006b). The gene FaOMT was mapped to the bottom of LG VII-F.1, linked to marker ChFaM160.…”

“…A number of these loci have been used in transgenic approaches to engineer volatile production (Beekwilder et al, 2004;Lunkenbein et al, 2006aLunkenbein et al, , 2006b). However, the desired effects have not always been obtained, as regulation of metabolic flux or substrate availability might be important parameters influencing their biosynthetic pathway.…”

Biosynthesis of plant‐derived flavor compounds

“…An ortho-diphenolic structure was identified as a common structural feature of the accepted substrates, and is also present in the dienolic tautomer of furaneol. Genetic transformation of strawberry with the FaOMT sequence in the antisense orientation, under the control of a constitutive promoter, resulted in a near total loss of methoxyfuraneol, demonstrating the in vivo methylation of furaneol by FaOMT (Lunkenbein et al, 2006). However, the reduced level of methoxyfuraneol was only perceived by one third of the volunteer panelists, consistent with results obtained by aroma extract dilution assays.…”