Differential screening of overexpressed genes involved in flavonoid biosynthesis in North American native grapes: 'Noble' muscadinia var. and 'Cynthiana' aestivalis var.

The expression of genes of the flavonoid biosynthesis pathway was studied in two major North American grape species Muscadinia rotundifolia ('Noble' var.) and Vitis aestivalis ('Cynthiana' var.) for two developmental stages''véraison' and 'physiological maturity'. For the first developmental stage green non-pigmented berries and dark pigmented berries were analyzed separately and were compared to each other as well as to physiologically matured berries. The study was divided into two parts. First microarray profiling was performed for 'Noble' by the use of high throughput 70-mers oligoarrays bearing a set of 14,562 Unigenes. The total number of transcripts that were differentially expressed in a given condition was 1,051. A slight increase in the number of expressed genes and in their mRNA accumulation levels from véraison towards physiologically matured berries was observed. A subset of 28 pertinent genes involved in critical steps of the flavonoid biosynthesis as well as significantly differentially expressed transcripts associated with muscadinia berry ripening were identified, and the change in their expression confirmed by RT-PCR. In the second part of the study the expression profiles of the 28 previously characterized genes were validated in 'Cynthiana' using the same RT-PCR technique. Unigenes from the flavonoid pathway reported to be associated with color development in vinifera grape were found to be differentially expressed in both 'Noble' and 'Cynthiana'. Amongst them chalcone synthase (isogene CHS3), glutathione S-transferase (isogene GST4), glucose-flavonoid 3-o-glucosyl transferase (UFGT), and anthocyanidin synthase (ANS) were particularly distinguishable. Thus it might be concluded that the global regulatory steps of the flavonoid pathway are conserved amongst V. vinifera, M. rotundifolia and V. aestivalis.