Transcriptome and Metabolome Analyses Provide Insights Into the Composition and Biosynthesis of Grassy Aroma Volatiles in White-Fleshed Pitaya

Advances in the Understanding of Postharvest Physiological Changes and the Storage and Preservation of Pitaya

Highly prized for its unique taste and appearance, pitaya is a tasty, low-calorie fruit. It has a high-water content, a high metabolism, and a high susceptibility to pathogens, resulting in an irreversible process of tissue degeneration or quality degradation and eventual loss of commercial value, leading to economic loss. High quality fruits are a key guarantee for the healthy development of economic advantages. However, the understanding of postharvest conservation technology and the regulation of maturation, and senescence of pitaya are lacking. To better understand the means of postharvest storage of pitaya, extend the shelf life of pitaya fruit and prospect the postharvest storage technology, this paper analyzes and compares the postharvest quality changes of pitaya fruit, preservation technology, and senescence regulation mechanisms. This study provides research directions for the development of postharvest storage and preservation technology.

Identification, characterization, and expression of lipoxygenase genes in sweet cherry (Prunus avium L.) cv. Regina and their relationship with the development of an herbaceous off-flavor during fruit ripening

Flavor is an essential characteristic of fruit quality and is significant for consumers. Off-flavors have been reported in several fruits, including sweet cherry. This fruit has been reported to show an herbaceous/grassy-like flavor. The herbaceous off-flavor in sweet cherries detected in cultivar Regina has been related to the differential development of aroma compounds such as short-chain aldehydes and esters. One of the main biosynthesis pathways for these compounds is the fatty acid oxidation mediated by lipoxygenases (LOX). In order to have a better understanding of the biological basis of the differences in the volatile profile, the LOX gene expression profile was characterized during fruit development with and without herbaceous off-flavor. A genome-wide analysis of LOX in sweet cherry was carried out and compared to other species such as Arabidopsis, tomato, apple, prunus and strawberry. The structural features of 9-LOX and 13-LOX genes, encoded protein domains and their synteny were examined. Moreover, we analyzed the LOX expression at four developmental stages along ripening by RT-qPCR. Thirteen LOX gene candidates (six 9-LOX and seven 13-LOX) were identified. The 13-LOXs, PaLOX10, PaLOX11, and PaLOX12 were differentially expressed in herbaceous sweet cherries. Furthermore, their expression profile positively correlated with key volatile compounds linked to the herbaceous off-flavor. Overall, this study involves the genome-wide characterization of the LOX family in Prunus avium cv. Regina and provides information that can aid in studying LOX-related fruit deterioration in sweet cherries and associated species.

Pitaya Virus X Coat Protein Acts as an RNA Silencing Suppressor and Can Be Used as a Specific Target for Detection Using RT-LAMP

Selenicereus undatus (Haworth) D.R. Hunt (pitaya) is a tropical fruit that has been commonly cultivated in Guizhou Province, China, in recent years due to its good taste and high nutritional value. This planting area currently ranks third in China. Viral diseases have increasingly emerged in pitaya cultivation because of the expansion of the pitaya planting area and the characteristics of asexual propagation. The spread of pitaya virus X (PiVX; a Potexvirus) is among the most severe viruses threatening the quality and yield of pitaya fruit. To investigate the occurrence of PiVX in pitaya cultivations in Guizhou Province, we developed a reverse transcription loop-mediated isothermal amplification (RT-LAMP) method that can detect PiVX with high sensitivity and specificity at a low cost and produce a visualized result. Our best RT-LAMP system was significantly more sensitive than RT-PCR and was highly specific to PiVX. Furthermore, PiVX coat protein (CP) can form a homodimer, and PiVX may use its CP as a plant RNA silencing suppressor to enhance infection. To the best of our knowledge, this is the first report of fast detection of PiVX and functional exploration of CP in a Potexvirus. These findings will provide an opportunity for early diagnosis and prevention of viruses in pitaya.

Metabolomics and transcriptomics analyses for characterizing the alkaloid metabolism of Chinese jujube and sour jujube fruits

Introduction

Jujube is an important economic forest tree whose fruit is rich in alkaloids. Chinese jujube (Ziziphus jujuba Mill.) and sour jujube (Ziziphus spinosa Hu.) are the two most important species of the jujube genus. However, the mechanisms underlying the synthesis and metabolism of alkaloids in jujube fruits remain poorly understood.

Methods

In this study, the fruits of Ziziphus jujuba 'Hupingzao' and Ziziphus spinosa 'Taigusuanzao' in different harvest stages were used as test materials, we first integrated widely targeted metabolomics and transcriptomics analyses to elucidate the metabolism of alkaloids of jujube fruits.

Results

In the metabolomics analysis, 44 alkaloid metabolites were identified in 4 samples, 3 of which were unique to sour jujube fruit. The differential alkaloid metabolites (DAMs) were more accumulated in sour jujube than in Chinese jujube; further, they were more accumulated in the white ripening stage than in the red stage. DAMs were annotated to 12 metabolic pathways. Additionally, transcriptomics data revealed 259 differentially expressed genes (DEGs) involved in alkaloid synthesis and metabolism. By mapping the regulatory networks of DAMs and DEGs, we screened out important metabolites and 11 candidate genes.

Discussion

This study preliminarily elucidated the molecular mechanism of jujube alkaloid synthesis. The candidate genes regulated the synthesis of key alkaloid metabolites, but the specific regulation mechanism is unclear. Taken together, our results provide insights into the metabolic networks of alkaloid synthesis in Chinese jujube and sour jujube fruits at different harvest stages, thereby providing a theoretical reference for further research on the regulatory mechanism of jujube alkaloids and their development and utilization.

Integrated metabolome and transcriptome analysis provides insights on the floral scent formation in Hydrangea arborescens

Hydrangea (Hydrangea arborescens var. 'Annabelle') flowers are composed of sweet aroma sepals rather than true petals and can change color. Floral volatiles play important roles in plants, such as attracting pollinators, defending against herbivores, and signaling. However, the biosynthesis and regulatory mechanisms underlying fragrance formation in H. arborescens during flower development remain unknown. In this study, a combination of metabolite profiling and RNA sequencing (RNA-seq) was employed to identify genes associated with floral scent biosynthesis mechanisms in 'Annabelle' flowers at three developmental stages (F1, F2, and F3). The floral volatile data revealed that the 'Annabelle' volatile profile includes a total of 33 volatile organic compounds (VOCs), and VOCs were abundant during the F2 stage of flower development, followed by the F1 and F3 stages, respectively. Terpenoids and benzenoids/phenylpropanoids were abundant during the F2 and F1 stages, with the latter being the most abundant, whereas fatty acid derivatives and other compounds were found in large amount during the F3 stage. According to ultra performance liquid chromatography - tandem mass spectrometer (UPLC-MS/MS) analysis, benzene and substituted derivatives, carboxylic acids and derivatives, and fatty acyls play a significant role in the floral metabolite profile. The transcriptome data revealed a total of 17,461 differentially expressed genes (DEGs), with 7,585, 12,795, and 9,044 DEGs discovered between the F2 and F1, F3 and F1, and F2 and F3 stages, respectively. Several terpenoids and benzenoids/phenylpropanoids biosynthesis-related DEGs were identified, and GRAS/bHLH/MYB/AP2/WRKY were more abundant among transcription factors (TFs). Finally, DEGs interlinked with VOCs compounds were determined using cytoscape and k-means analysis. Our results paves the way for the discovery of new genes, critical data for future genetic studies, and a platform for the metabolic engineering of genes involved in the production of Hydrangea's signature floral fragrance.

Optimization of strains for fermentation of kiwifruit juice and effects of mono- and mixed culture fermentation on its sensory and aroma profiles

In this study, a quality evaluation model of fermented kiwifruit juice (KJ) based on strain growth characteristics, sensory quality and functional characteristics was established by PCA, and the effects of mono- and mixed culture fermentation on the sensory and aroma profiles of KJ were comparatively studied. Experiments determined that L. brevis (LB) was the optimal strain for monoculture fermentation, and L. plantarum (LP2):LB = 1:2 was the optimum ratio for mixed fermentation. The results showed that lactic acid bacteria (LAB) fermentation significantly reduced the pH, soluble solid content and lightness, and improved its functional characteristics and viscosity. Mixed culture fermentation was superior to monoculture fermentation in terms of colony counts, sensory quality and viscosity. In general, after LAB fermentation, the concentrations of esters, ketones, alcohols and terpenoids in KJ increased significantly, while the concentrations of aldehydes decreased significantly. The production of esters and terpenoids was more strongly promoted by monoculture fermentation, while mixed culture fermentation promoted the production of more ketones and alcohols. 2,5-octanedione and 1-octen-3-ol could be the characteristic aroma compounds of mixed fermented KJ.