Abstract
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.
Highlights
Flavonoids compose a major class of plant polyphenolic compounds and can be divided into three categories: anthocyanins, proanthocyanidins (PAs) and flavonols (Williams and Grayer, 2004)
We found via high-pressure liquid chromatography (HPLC) analysis that the accumulation of PAs was enriched in young fruits during fruit development
We used RNA-seq analysis to focus on the molecular mechanisms underlying PA biosynthesis during fruit development
Summary
Flavonoids compose a major class of plant polyphenolic compounds and can be divided into three categories: anthocyanins, proanthocyanidins (PAs) and flavonols (Williams and Grayer, 2004). The transcript levels of the LAR and ANR genes were significantly correlated with the contents of catechin and epicatechin, respectively, which suggests that they play important roles in PA synthesis (Liao et al, 2015). Two LAR genes, MrLAR1 and MrLAR2, and two ANR genes, MrANR1 and MrANR2, have been identified in crabapple. Overexpressing these four genes in tobacco leaves (Nicotiana tabacum) increased the PA content, and silencing them in crabapple plants inhibited the accumulation of PAs (Li et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
