SummaryFruit ripening is characterized by dramatic changes in gene expression, enzymatic activities and metabolism. Although the process of ripening has been studied extensively, we still lack valuable information on how the numerous metabolic pathways are regulated and co-ordinated. In this paper we describe the characterization of FaMYB1, a ripening regulated strawberry gene member of the MYB family of transcription factors. Flowers of transgenic tobacco lines overexpressing FaMYB1 showed a severe reduction in pigmentation. A reduction in the level of cyanidin 3-rutinoside (an anthocyanin) and of quercetin-glycosides (¯avonols) was observed. Expression of late¯avonoid biosynthesis genes and their enzyme activities were aversely affected by FaMYB1 overexpression. Two-hybrid assays in yeast showed that FaMYB1 could interact with other known anthocyanin regulators, but it does not act as a transcriptional activator. Interestingly, the C-terminus of FaMYB1 contains the motif pdLNL D / E Lxi G / S . This motif is contained in a region recently proposed to be involved in the repression of transcription by AtMYB4, an Arabidopsis MYB protein. Our results suggest that FaMYB1 may play a key role in regulating the biosynthesis of anthocyanins and¯avonols in strawberry. It may act to repress transcription in order to balance the levels of anthocyanin pigments produced at the latter stages of strawberry fruit maturation, and/or to regulate metabolite levels in various branches of the¯avonoid biosynthetic pathway.

Fruit flavor is a result of a complex mixture of numerous compounds. The formation of these compounds is closely correlated with the metabolic changes occurring during fruit maturation. Here, we describe the use of DNA microarrays and appropriate statistical analyses to dissect a complex developmental process. In doing so, we have identified a novel strawberry alcohol acyltransferase ( SAAT ) gene that plays a crucial role in flavor biogenesis in ripening fruit. Volatile esters are quantitatively and qualitatively the most important compounds providing fruity odors. Biochemical evidence for involvement of the SAAT gene in formation of fruity esters is provided by characterizing the recombinant protein expressed in Escherichia coli . The SAAT enzyme showed maximum activity with aliphatic medium-chain alcohols, whose corresponding esters are major components of strawberry volatiles. The enzyme was capable of utilizing short-and medium-chain, branched, and aromatic acyl-CoA molecules as cosubstrates. The results suggest that the formation of volatile esters in fruit is subject to the availability of acyl-CoA molecules and alcohol substrates and is dictated by the temporal expression pattern of the SAAT gene(s) and substrate specificity of the SAAT enzyme(s).

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Fruit flavor is a result of a complex mixture of numerous compounds. The formation of these compounds is closely correlated with the metabolic changes occurring during fruit maturation. Here, we describe the use of DNA microarrays and appropriate statistical analyses to dissect a complex developmental process. In doing so, we have identified a novel strawberry alcohol acyltransferase (SAAT) gene that plays a crucial role in flavor biogenesis in ripening fruit. Volatile esters are quantitatively and qualitatively the most important compounds providing fruity odors. Biochemical evidence for involvement of the SAAT gene in formation of fruity esters is provided by characterizing the recombinant protein expressed in Escherichia coli. The SAAT enzyme showed maximum activity with aliphatic medium-chain alcohols, whose corresponding esters are major components of strawberry volatiles. The enzyme was capable of utilizing short- and medium-chain, branched, and aromatic acyl-CoA molecules as cosubstrates. The results suggest that the formation of volatile esters in fruit is subject to the availability of acyl-CoA molecules and alcohol substrates and is dictated by the temporal expression pattern of the SAAT gene(s) and substrate specificity of the SAAT enzyme(s).

Using cDNA microarrays, a comprehensive investigation of gene expression was carried out in strawberry (Fragaria ϫ ananassa) fruit to understand the flow of events associated with its maturation and non-climacteric ripening. We detected key processes and novel genes not previously associated with fruit development and ripening, related to vascular development, oxidative stress, and auxin response. Microarray analysis during fruit development and in receptacle and seed (achene) tissues established an interesting parallelism in gene expression between the transdifferentiation of tracheary elements in Zinnia elegans and strawberry. One of the genes, CAD, common to both systems and encoding the lignin-related protein cinnamyl alcohol dehydrogenase, was immunolocalized to immature xylem cells of the vascular bundles in the strawberry receptacle. To examine the importance of oxidative stress in ripening, gene expression was compared between fruit treated on-vine with a free radical generator and non-treated fruit. Of 46 genes induced, 20 were also ripening regulated. This might suggest that active gene expression is induced to cope with oxidative stress conditions during ripening or that the strawberry ripening transcriptional program is an oxidative stress-induced process. To gain insight into the hormonal control of non-climacteric fruit ripening, an additional microarray experiment was conducted comparing gene expression in fruit treated exogenously with auxin and control fruit. Novel auxin-dependent genes and processes were identified in addition to transcriptional programs acting independent of auxin mainly related to cell wall metabolism and stress response.