Berry skin development in Norton grape: Distinct patterns of transcriptional regulation and flavonoid biosynthesis
Authors: Ali Mohammad B , Howard Susanne , Chen Shangwu , Wang Yechun , Yu Oliver , Kovacs Laszlo G , Qiu Wenping 
Published: January 2011

Background

The complex and dynamic changes during grape berry development have been studied inVitis vinifera, but little is known about these processes in otherVitisspecies. The grape variety 'Norton', with a major portion of its genome derived fromVitis aestivalis, maintains high levels of malic acid and phenolic acids in the ripening berries in comparison withV. viniferavarieties such as Cabernet Sauvignon. Furthermore, Norton berries develop a remarkably high level of resistance to most fungal pathogens while Cabernet Sauvignon berries remain susceptible to those pathogens. The distinct characteristics of Norton and Cabernet Sauvignon merit a comprehensive analysis of transcriptional regulation and metabolite pathways.

Results

A microarray study was conducted on transcriptome changes of Norton berry skin during the period of 37 to 127 days after bloom, which represents berry developmental phases from herbaceous growth to full ripeness. Samples of six berry developmental stages were collected. Analysis of the microarray data revealed that a total of 3,352 probe sets exhibited significant differences at transcript levels, with two-fold changes between at least two developmental stages. Expression profiles of defense-related genes showed a dynamic modulation of nucleotide-binding site-leucine-rich repeat (NBS-LRR) resistance genes and pathogenesis-related (PR) genes during berry development. Transcript levels ofPR-1in Norton berry skin clearly increased during the ripening phase. As in other grapevines, genes of the phenylpropanoid pathway were up-regulated in Norton as the berry developed. The most noticeable was the steady increase of transcript levels of stilbene synthase genes. Transcriptional patterns of six MYB transcription factors and eleven structural genes of the flavonoid pathway and profiles of anthocyanins and proanthocyanidins (PAs) during berry skin development were analyzed comparatively in Norton and Cabernet Sauvignon. Transcriptional patterns ofMYB5AandMYB5Bwere similar during berry development between the two varieties, but those ofMYBPA1andMYBPA2were strikingly different, demonstrating that the general flavonoid pathways are regulated under different MYB factors. The data showed that there were higher transcript levels of the genes encoding flavonoid-3'-O-hydroxylase (F3'H), flavonoid-3',5'-hydroxylase (F3'5'H), leucoanthocyanidin dioxygenase(LDOX), UDP-glucose:flavonoid 3'-O-glucosyltransferase (UFGT), anthocyanidin reductase (ANR), leucoanthocyanidin reductase (LAR)1andLAR2in berry skin of Norton than in those of Cabernet Sauvignon. It was also found that the total amount of anthocyanins was markedly higher in Norton than in Cabernet Sauvignon berry skin at harvest, and five anthocyanin derivatives and three PA compounds exhibited distinctive accumulation patterns in Norton berry skin.

Conclusions

This study provides an overview of the transcriptome changes and the flavonoid profiles in the berry skin of Norton, an important North American wine grape, during berry development. The steady increase of transcripts ofPR-1and stilbene synthase genes likely contributes to the developmentally regulated resistance during ripening of Norton berries. More studies are required to address the precise role of each stilbene synthase gene in berry development and disease resistance. Transcriptional regulation ofMYBA1,MYBA2,MYB5AandMYBPA1as well as expression levels of their putative targetsF3'H, F3'5'H, LDOX,UFGT,ANR, LAR1, andLAR2are highly correlated with the characteristic anthocyanin and PA profiles in Norton berry skin. These results reveal a unique pattern of the regulation of transcription and biosynthesis pathways underlying the viticultural and enological characteristics of Norton grape, and yield new insights into the understanding of the flavonoid pathway in non-vinifera grape varieties.