Transcriptomic Analysis Reveals Genes Associated with the Regulation of Peach Fruit Softening and Senescence during Storage

Selection of stable reference genes in prunus persica fruit infected with monilinia laxa for normalisation of RT-qPCR gene expression data

Reverse transcription-quantitative PCR (RT-qPCR) is a powerful tool for quantifying gene expression. However, reference genes (RGs) for gene expression analysis in peach (Prunus persica) during interactions with Monilinia laxa, a major fungal pathogen that causes brown rot, have not been established. In this study, we analysed 12 candidate RGs in this pathosystem by analysing samples from 12 to 144 HAI. The stability of the RGs was evaluated using the ΔCq method and BestKeeper, NormFinder, and geNorm algorithms. Our results identified AKT3, RNA pol II (RPII) and SNARE (using geNorm), RPII, AKT3 and TEF2 (using NormFinder), AKT3, SNARE and RPII (using BestKeeper) and RPII, MUB6 and AKT3 (using the ΔCq method) as the most stable RGs for mRNA normalisation in this pathosystem across all tested samples. The geNorm algorithm was used to determine the optimal number of suitable RGs required for proper normalisation under these experimental conditions, indicating that the three RGs were sufficient for normalisation. Analysis of the results obtained using different algorithms showed that AKT3, RPII, and SNARE were the three most stable RGs. Furthermore, to confirm the validity of the reference genes, the expression levels of six genes of interest, involved in different metabolic pathways, were normalized in inoculated and uninoculated peach fruit. These findings provide a set of RGs for accurate RT-qPCR analysis in studies involving peach and M. laxa interactions, facilitating deeper insights into the molecular mechanisms underlying this important plant-pathogen relationship.

Identification of potential molecular markers for detection of lengthy chilled storage of Prunus persica L. fruit

Low temperature is the main strategy to preserve fruit quality post-harvest, in the supply chain. Low temperatures reduce the respiration, ethylene emission, and enzymatic activities associated with senescence. Unfortunately, peaches are sensitive to low temperatures if exposed for long periods, resulting in physiological disorders that can compromise commercial quality. Maximum damage occurs at 5 °C while at 1 °C damage is reduced. Therefore, rapid early detection methods for the distribution chain to monitor length and temperature of fruit storage are needed. The aim of this work was to identify candidate genes to develop an antibody-based marker system in peach fruit to monitor chilled storage. Two cultivars were tested: 'Sagittaria', an early ripening peach, and 'Big Top' a mid-season ripening nectarine, with delayed softening and resistance to supply-chain conditions. Both cultivars were subjected to 1 or 5 °C chilled storage for different times to simulate typical supply-chain conditions. Identification and expression of potential marker genes was assessed using a previous transcriptomic study following storage at 1 °C. Fifteen candidate genes were selected, however only seven proteins encoded were suitable as protein markers as they lack a transmembrane domain. Real-time qPCR using fruit from the subsequent year to the transcriptome was used to assess expression at both 1 and 5 °C chilled storage of five candidate genes. Four genes and the related proteins were identified that would be suitable for the development of molecular markers: a Pathogenesis-Related Bet v I family protein, a dehydrin, a Glycosyl hydrase family 18 protein and a Late Embryogenesis abundant protein.

Two NAC transcription factors regulated fruit softening through activating xyloglucan endotransglucosylase/hydrolase genes during kiwifruit ripening

Kiwifruit is a climacteric fruit that is prone to ripening and softening. Understanding molecular regulatory mechanism of kiwifruit softening, is helpful to ensure long-term storage of fruit. In the study, two NAC TFs and two XTH genes were isolated from kiwifruit. Phylogenetic tree showed that both AcNAC1 and AcNAC2 belonged to NAP subfamily, AcXTH1 belong to I subfamily, and AcXTH2 belong to III subfamily. Bioinformatics analysis predicted that AcNAC1 and AcNAC2 possessed similar three-dimensional structural, and belonged to hydrophilic proteins. AcXTH1 and AcXTH2 were hydrophilic proteins and contained signal peptides. AcXTH1 had a transmembrane structure, but AcXTH2 did not. qRT-PCR results showed that AcNAC1, AcNAC2, AcXTH1 and AcXTH2 were increased during kiwifruit ripening. Correlation analysis showed that kiwifruit softening was closely related to endotransglucosylase/hydrolase genes and NAC TFs, as well as there was also a close relationship between AcXTHs and AcNACs. Moreover, both AcNAC1 and AcNAC2 were transcriptional activators located in nucleus, which bound to and activated the promoters of AcXTH1 and AcXTH2. In shortly, we proved that the roles of NAC TFs in mediating fruit softening during kiwifruit ripening. Altogether, our results clarified that AcNAC1 and AcNAC2 were transcriptional activators, and took part in kiwifruit ripening and softening through activating endotransglucosylase/hydrolase genes, providing a new insight of fruit softening network in kiwifruit ripening.