BCH1 expression pattern contributes to the fruit carotenoid diversity between peach and apricot

Peach (Prunus persica L. Batsch) and apricot (Prunus armeniaca L.) are two species of economic importance for fruit production in the genus Prunus. Peach and apricot fruits exhibit significant differences in carotenoid levels and profiles. HPLC-PAD analysis showed that a greater content of β-carotene in mature apricot fruits is primarily responsible for orange color, while peach fruits showed a prominent accumulation of xanthophylls (violaxanthin and cryptoxanthin) with yellow color. There are two β-carotene hydroxylase genes in both peach and apricot genomes. Transcriptional analysis revealed that BCH1 expresses highly in peach but lowly in apricot fruit, showing a correlation with peach and apricot fruit carotenoid profiles. By using a carotenoid engineered bacterial system, it was demonstrated that there was no difference in the BCH1 enzymatic activity between peach and apricot. Comparative analysis about the putative cis-acting regulatory elements between peach and apricot BCH1 promoters provided important information for our understanding of the differences in promoter activity of the BCH1 genes in peach and apricot. Therefore, we investigated the promoter activity of BCH1 gene through a GUS detection system, and confirmed that the difference in the transcription level of the BCH1 gene resulted from the difference of the promoter function. This study provides important perspective to understanding the diversity of carotenoid accumulation in Prunus fruits such as peach and apricot. In particular, BCH1 gene is proposed as a main predictor for β-carotene content in peach and apricot fruits during the ripening process.

Transcriptional regulatory networks controlling taste and aroma quality of apricot (Prunus armeniaca L.) fruit during ripening

BACKGROUND

Taste and aroma, which are important organoleptic qualities of apricot (Prunus armeniaca L.) fruit, undergo rapid and substantial changes during ripening. However, the associated molecular mechanisms remain unclear. The goal of this study was to identify candidate genes for flavor compound metabolism and to construct a regulatory transcriptional network.

RESULTS

We characterized the transcriptome of the 'Jianali' apricot cultivar, which exhibits substantial changes in flavor during ripening, at 50 (turning), 73 (commercial maturation) and 91 (full ripe) days post anthesis (DPA) using RNA sequencing (RNA-Seq). A weighted gene co-expression network analysis (WGCNA) revealed that four of 19 modules correlated highly with flavor compound metabolism (P < 0.001). From them, we identified 1237 differentially expressed genes, with 16 intramodular hubs. A proposed pathway model for flavor compound biosynthesis is presented based on these genes. Two SUS1 genes, as well as SPS2 and INV1 were correlated with sugar biosynthesis, while NADP-ME4, two PK-like and mitochondrial energy metabolism exerted a noticeable effect on organic acid metabolism. CCD1 and FAD2 were identified as being involved in apocarotenoid aroma volatiles and lactone biosynthesis, respectively. Five sugar transporters (Sweet10, STP13, EDR6, STP5.1, STP5.2), one aluminum-activated malate transporter (ALMT9) and one ABCG transporter (ABCG11) were associated with the transport of sugars, organic acids and volatiles, respectively. Sixteen transcription factors were also highlighted that may also play regulatory roles in flavor quality development.

CONCLUSIONS

Apricot RNA-Seq data were obtained and used to generate an annotated set of predicted expressed genes, providing a platform for functional genomic research. Using network analysis and pathway mapping, putative molecular mechanisms for changes in apricot fruit taste and aroma during ripening were elucidated.