The age pathway is important for regulating flower bud initiation in flowering plants. The major regulators in this pathway are miR156 and SPL transcription factors. To date, SPL genes have been identified in many species of plants. Loquat, as a woody fruit tree of Rosaceae, is unique in flowering time as it blooms in winter. However, the study of its SPL homologous genes on the regulation mechanism of flowering time is still limited. In this study, four SPL homologs—EjSPL3, EjSPL4, EjSPL5, and EjSPL9—are cloned from loquat, and phylogenetic analysis showed that they share a high sequence similarity with the homologues from other plants, including a highly conserved SQUAMOSA promoter binding protein (SBP)-box domain. EjSPL3, EjSPL4, EjSPL5 are localized in the cytoplasm and nucleus, and EjSPL9 is localized only in the nucleus. EjSPL4, EjSPL5, and EjSPL9 can significantly activate the promoters of EjSOC1-1, EjLFY-1, and EjAP1-1; overexpression of EjSPL3, EjSPL4, EjSPL5, and EjSPL9 in wild-type Arabidopsis thaliana can promote flowering obviously, and downstream flowering genes expression were upregulated. Our work indicated that the EjSPL3, EjSPL4, EjSPL5, and EjSPL9 transcription factors are speculated to likely participate in flower bud differentiation and other developmental processes in loquat. These findings are helpful to analyze the flowering regulation mechanism of loquat and provide reference for the study of the flowering mechanism of other woody fruit trees.

Passion fruit (Passiflora edulis) possesses a complex aroma and is widely grown in tropical and subtropical areas. Here, we conducted the de novo assembly, annotation and comparison of purple (P. edulis Sims) and yellow passion fruit (P. edulis f. flavicarpa) reference genomes using PacBio, Illumina and Hi-C technologies. Notably, we discovered evidence of recent whole-genome duplication events in P. edulis genomes. Comparative analysis revealed 7.6∼8.1 million single nucleotide polymorphisms, one million insertions/deletions, and over 142 Mb presence/absence variations among different P. edulis genomes. During the ripening of yellow passion fruit, metabolites related to flavor, aroma, and color were substantially accumulated or changed. Through joint analysis of genomic variations, differentially expressed genes, and accumulated metabolites, we explored candidate genes associated with flavor, aroma and color distinctions. Flavonoid biosynthesis pathways, anthocyanin biosynthesis pathways and related metabolites are pivotal factors affecting the coloration of passion fruit, and terpenoids metabolites accumulated more in purple passion fruit. Finally, by heterologous expression in yeast (Saccharomyces cerevisiae), we functionally characterized 12 terpene synthases (TPSs). Our findings revealed that certain TPS homologues in both yellow and purple passion fruit varieties produce identical terpene products, while others yield distinct compounds or even lose their functionality. These discoveries revealed the genetic and metabolic basis of unique characteristics in aroma and flavor between the two passion fruit varieties. This study provides resources for better understanding the genome architecture and accelerating genetic improvement of passion fruits.

Fresh-cut fruit and vegetables are becoming increasingly popular as fresh food products, valued for their convenience, health benefits, and ready-to-eat nature (1).Unlike intact produce, fresh-cut fruit and vegetables undergo various processing operations, such as peeling, slicing and dicing, prior to consumption and storage in market. Consequently, they are more susceptible to decay and discoloration, leading to a relatively short shelf life (2). Among these challenges, browning presents one of the most significant issues in the fresh-cut industry (3), resulting in an undesirable dark coloration. Such browning not only diminishes the visual appeal but also adversely impacts consumers' acceptance (4). Furthermore, certain compounds, particularly phenolic compounds, serve as essential sources of antioxidants in fruit and vegetables. The oxidation of these phenolic compounds during the browning process inevitably results in a loss of antioxidant capacity in fresh-cut products, ultimately diminishing their associated health benefits (5). Therefore, understanding the browning mechanisms of fresh-cut produce is essential for the sustainable development of the fresh-cut industry and for producing high-quality products that meet consumers' expectations.Over the past three decades, considerable progress has been made in understanding the browning mechanisms of fresh-cut produce, particularly concerning the roles of phenolases in the browning reaction (6). However, the specific roles of phenylalanine ammonia-lyase (PAL) in the browning of fresh-cut produce remain ambiguous, and its potential as a target for browning control strategies has not been sufficiently explored. This opinion article aims to delve into the nuanced roles of PAL in enzymatic browning, emphasizing its potential implications for regulating the browning development of fresh-cut fruit and vegetables.It is widely recognized that food browning can be categorized into two distinct types: enzymatic and non-enzymatic browning (7). The latter occurs predominantly during the heating of food and is exemplified by processes such as the Maillard reaction and caramelization. In contrast, enzymatic reactions are the primary contributors to browning in fresh-cut fruit and vegetables (8).Fresh-cut produce experiences extensive mechanical injury, which compromises the integrity of the cell membrane and leads to the leakage of cellular contents and exposure to oxygen (9,10). This enzymatic browning process is initiated when phenolmetabolizing enzymes, such as polyphenol oxidase (PPO) and peroxidase (POD), come into direct contact with phenolic compounds in the presence of oxygen, resulting in phenolic oxidation and the subsequent formation of brown pigments (11, 12). Accordingly, current strategies employed for controlling browning in fresh-cut products focus primarily on regulating PPO activity.However, some studies have indicated that PPO or POD activity are not always directly correlated with the browning rate in fresh-cut products. For instance, a study of five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta) revealed varying susceptibility to browning, yet there was no significant correlation between the rate or degree of browning and the activities of PPO and POD in fresh-cut potatoes (13). In another study involving fresh-cut Chinese water chestnuts, treatments with both exogenous ascorbic acid (AsA) and ferulic acid (FA) were found to effectively inhibit the activities of PPO and POD during storage. However, only FA treatment was effective in reducing browning, while AsA treatment did not show a significant effect (14). In comparison to normal mango fruit, the total phenolic concentration in underskin browning mango exhibited a 7.4% increase, while the activities of PPO and POD decreased by 19.0% (15). These researches together suggest that, in addition to PPO or POD, other important factors also have significant roles in the browning of fresh-cut produce.Fresh-cut processing, often referred to as minimal processing, represents a form of wounding stress that induces mechanical injury to the intact fruit or vegetable (16).In response to wounding stress, plants activate a range of defense mechanisms designed to mitigate the effects of injury. Among the various strategies employed by plants, the phenylpropanoid pathway plays a crucial role in synthesizing protective compounds in response to wounding stress. This pathway is responsible for the production of a diverse array of secondary metabolites, including flavonoids and other phenolic compounds (17). Phenolic compounds and flavonoids in wounded fresh-cut fruit and vegetables are produced rapidly, partly to facilitate lignin synthesis as a response to wounding stress (16).PAL is the first enzyme in the phenylpropanoid pathway, responsible for converting L-phenylalanine into a range of phenolic compounds, such as phenols, phenolic acids, anthocyanins, flavonoids, isoflavones, and other polyphenolic metabolites in plants (18,19). It is well documented that wounding stress induces PAL activity and gene expression in fresh-cut products (16). Studies had shown that the expression levels of four PAL genes, as well as PAL activity, were significantly elevated in fresh-cut lettuce stems following wounding (20). In fresh-cut taro, PAL activities and the expression of three PAL genes increased at 3 d compared to 0 d, indicating that slicing induces PALs expression in fresh-cut taro (21).During the browning process of fresh-cut peaches, the activities of PAL, cinnamate-4-hydroxylase (C4H), and 4-coumarate: CoA ligase (4CL), two key enzymes in the phenylpropanoid pathway, were found to increase with the extent of browning, while hydrogen sulfide (H2S) treatment significantly inhibited both browning and these enzyme activities (22). Similar results regarding the induction of PAL through minimal processing have been observed in fresh-cut apples (23), lettuce stems (24), potatoes (25)...

Flowering plants have evolved different flowering habits to sustain long-term reproduction. Most woody trees experience dormancy and then bloom in the warm spring, but loquat blooms in the cold autumn and winter. To explore its mechanism of flowering regulation, we cloned two SHORT VEGETATIVE PHASE (SVP) homologous genes from ‘Jiefanzhong’ loquat (Eriobotrya japonica Lindl.), namely, EjSVP1 and EjSVP2. Sequence analysis revealed that the EjSVPs were typical MADS-box transcription factors and exhibited a close genetic relationship with other plant SVP/DORMANCY-ASSOCIATED MADS-BOX (DAM) proteins. The temporal and spatial expression patterns showed that EjSVP1 and EjSVP2 were mainly expressed in the shoot apical meristem (SAM) after the initiation of flowering; after reaching their highest level, they gradually decreased with the development of the flower until they could not be detected. EjSVP1 expression levels were relatively high in young tissues, and EjSVP2 expression levels were relatively high in young to mature transformed tissues. Interestingly, EjSVP2 showed relatively high expression levels in various flower tissues. We analyzed the EjSVP promoter regions and found that they did not contain the C-repeat/dehydration-responsive element. Finally, we overexpressed the EjSVPs in wild-type Arabidopsis thaliana Col-0 and found no significant changes in the number of rosette leaves of Arabidopsis thaliana; however, overexpression of EjSVP2 affected the formation of Arabidopsis thaliana flower organs. In conclusion, EjSVPs were found to play an active role in the development of loquat flowering. These findings may provide a reference for exploring the regulation mechanisms of loquat flowering and the dormancy mechanisms of other plants.