Transcriptomic Analysis on the Peel of UV-B-Exposed Peach Fruit Reveals an Upregulation of Phenolic- and UVR8-Related Pathways

Abstract

UV-B treatment deeply influences plant physiology and biochemistry, especially by activating the expression of responsive genes involved in UV-B acclimation through a UV-B-specific perception mechanism. Although the UV-B-related molecular responses have been widely studied in Arabidopsis, relatively few research reports deepen the knowledge on the influence of post-harvest UV-B treatment on fruit. In this work, a transcriptomic approach is adopted to investigate the transcriptional modifications occurring in the peel of UV-B-treated peach (Prunus persica L., cv Fairtime) fruit after harvest. Our analysis reveals a higher gene regulation after 1 h from the irradiation (88% of the differentially expressed genes-DEGs), compared to 3 h recovery. The overexpression of genes encoding phenylalanine ammonia-lyase (PAL), chalcone syntase (CHS), chalcone isomerase (CHI), and flavonol synthase (FLS) revealed a strong activation of the phenylpropanoid pathway, resulting in the later increase in the concentration of specific flavonoid classes, e.g., anthocyanins, flavones, dihydroflavonols, and flavanones, 36 h after the treatment. Upregulation of UVR8-related genes (HY5, COP1, and RUP) suggests that UV-B-triggered activation of the UVR8 pathway occurs also in post-harvest peach fruit. In addition, a regulation of genes involved in the cell-wall dismantling process (PME) is observed. In conclusion, post-harvest UV-B exposure deeply affects the transcriptome of the peach peel, promoting the activation of genes implicated in the biosynthesis of phenolics, likely via UVR8. Thus, our results might pave the way to a possible use of post-harvest UV-B treatments to enhance the content of health-promoting compounds in peach fruits and extending the knowledge of the UVR8 gene network.

Keywords: Prunus persica; UV-B radiation; flavonoids; metabolomics; secondary metabolism; transcriptomics.

Figure 1

Venn diagram for over- and under-expressed genes detected in the peel of UV-B-treated peach fruit after 1 h and 3 h from the end of UVB exposure.

Figure 2

Schematization of metabolic pathway for phenylpropanoid (a), flavonoid (b), and circadian rhythm (c), as described by KEGG 111 after 1 h and 3 h from the end of UVB exposure in the peel of UV-B-treated peach fruit. Arrows indicate the path from reagent to product. Red arrows underline genes encoding for enzyme that resulted in being over-expressed after 1 h of recovery; similarly, green arrows underline over-expressed genes after 3 h of recovery; yellow arrows are over-expressed DEGs active during both recovery times. Black arrows are for not-differentially expressed genes in the related pathways. No under-expressed genes were retrieved for the investigated pathways. Genes involved in the metabolic pathway are written in italics. Concerning the circadian rhythm map (c), genes involved in cellular regulation are within the square.

Figure 3

MapMan schematization for DEGs found in the peel of UV-B-treated peach fruit after 1 and 3 h of recovery. Red dots represent the over-expressed genes (OE), whereas blue dots are under-expressed ones (UE). White dots indicate genes that were not differentially expressed in one time point but in the other. The scale, based on gene fold change, spans from dark blue (Log FC = −3) to dark red (Log FC = 3).

Figure 4

VisAnt gene network of (a) “Red” and (b) “Salmon” co-expression modules detected with WGNA. Each node represents a gene, interactions between nodes are shown as lines.

Figure 5

Summary of the molecular and biochemical responses of post-harvest peach fruit irradiated with UV-B and the UVR8 pathway model [3].