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Transcriptional analysis of apple fruit proanthocyanidin biosynthesis.

ABSTRACT: Proanthocyanidins (PAs) are products of the flavonoid pathway, which also leads to the production of anthocyanins and flavonols. Many flavonoids have antioxidant properties and may have beneficial effects for human health. PAs are found in the seeds and fruits of many plants. In apple fruit (Malus × domestica Borkh.), the flavonoid biosynthetic pathway is most active in the skin, with the flavan-3-ols, catechin, and epicatechin acting as the initiating units for the synthesis of PA polymers. This study examined the genes involved in the production of PAs in three apple cultivars: two heritage apple cultivars, Hetlina and Devonshire Quarrenden, and a commercial cultivar, Royal Gala. HPLC analysis shows that tree-ripe fruit from Hetlina and Devonshire Quarrenden had a higher phenolic content than Royal Gala. Epicatechin and catechin biosynthesis is under the control of the biosynthetic enzymes anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR1), respectively. Counter-intuitively, real-time quantitative PCR analysis showed that the expression levels of Royal Gala LAR1 and ANR were significantly higher than those of both Devonshire Quarrenden and Hetlina. This suggests that a compensatory feedback mechanism may be active, whereby low concentrations of PAs may induce higher expression of gene transcripts. Further investigation is required into the regulation of these key enzymes in apple.

SUBMITTER: Henry-Kirk RA

PROVIDER: S-EPMC3444262 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Transcriptional analysis of apple fruit proanthocyanidin biosynthesis.

Henry-Kirk Rebecca A RA McGhie Tony K TK Andre Christelle M CM Hellens Roger P RP Allan Andrew C AC

Journal of experimental botany 20120801 15

Proanthocyanidins (PAs) are products of the flavonoid pathway, which also leads to the production of anthocyanins and flavonols. Many flavonoids have antioxidant properties and may have beneficial effects for human health. PAs are found in the seeds and fruits of many plants. In apple fruit (Malus × domestica Borkh.), the flavonoid biosynthetic pathway is most active in the skin, with the flavan-3-ols, catechin, and epicatechin acting as the initiating units for the synthesis of PA polymers. Thi ...[more]

PMID: 22859681

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Project description:Proanthocyanidins (PAs) are a class of flavonoid compounds in plants that play many important roles in pest and disease resistance and are beneficial components of the human diet. The crabapple (Malus) provides an excellent model to study PA biosynthesis and metabolism; therefore, to gain insights into the PA regulatory network in Malus plants, we performed RNA-seq profiling of fruits of the 'Flame' cultivar at five sequential developmental stages. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis showed that differentially expressed genes (DEGs) related to the functional category 'plant hormone signal transduction' were significantly enriched during fruit development. Further analysis showed that ethylene signal transduction pathway genes or response genes, such as ERS (ethylene response sensor), EIN3 (ETHYLENE INSENSITIVE 3) and ERFs (ethylene response factors), may play an important role in the regulatory network of PA biosynthesis. Additionally, 12 DEGs, including 10 ERFs, 1 MYB, and 1 bHLH transcription factor, associated with PA biosynthesis were identified using WGCNA. The expression patterns of these genes correlated with PA accumulation trends and transcriptome data from qRT-PCR analysis. The expression of RAP2-4 (RELATED TO APETALA 2-4) and RAV1 (related to ABI3/VP1), which belong to the ERF transcription factor family, showed the greatest correlations with PAs accumulation among the 12 identified TFs. Agrobacterium mediated-transient overexpression of the RAP2-4 led to an increase in PA abundance in crabapple leaves and apple fruits, and the opposite results were observed in RAV1-overexpressed crabapple leaves and apple fruits. Moreover, a yeast one-hybrid assay showed that RAP2-4 and RAV1 specifically bound the promoters of the PA biosynthetic genes McLAR1 and McANR2, respectively. These results indicate that RAP2-4 act as an inducer and RAV1 act as a repressor of PA biosynthesis by regulating the expression of the PA biosynthetic genes McLAR1 and McANR2. Taken together, we identified two potential regulators of PA biosynthesis and provide new insights into the ethylene-PA regulatory network.

Dataset Information

Transcriptional analysis of apple fruit proanthocyanidin biosynthesis.

Publications

Transcriptional analysis of apple fruit proanthocyanidin biosynthesis.

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