Molecular Plant Breeding 2025, Vol.16, No.3, 202-210 http://genbreedpublisher.com/index.php/mpb 204 The aroma of golden pitaya is relatively light, mainly grassy, and its volatile organic compounds mainly include alcohols (such as 1-hexanol), aldehydes (such as hexanal) and esters (such as hexyl acetate). During the ripening process, the accumulation of C6 alcohols and aldehydes increases, especially hexanal and 1-hexanol with a grassy aroma, and their concentration plays a decisive role in the flavor differences of different strains (Wu et al., 2022). 2.2 Key metabolic pathways and regulatory genes In terms of carbohydrate metabolism, the accumulation of sugar in golden pitaya involves sucrose synthase (SUSY) and cell wall invertase (CWIN), and efficient transport and distribution of fruit sugar is achieved through sugar transporters such as SWEETs and TSTs. Protein kinases such as CDPKs that regulate the activity of these enzymes are important negative regulators that affect the accumulation of fructose and glucose (Wang et al., 2021). Organic acid synthesis is mainly through the tricarboxylic acid cycle (TCA), and citrate synthase (CS) and malate dehydrogenase (MDH) are the core enzyme systems that control the production of citric acid and malic acid. In addition, members of the ALMT (aluminum-activated membrane protein) family on the vacuole membrane participate in the transmembrane transport of organic acids such as malic acid and determine their accumulation level in the vacuole (Miao et al., 2024). In terms of aromatic substances, the main aroma compounds are synthesized through the fatty acid cleavage pathway, involving key enzymes such as lipoxygenase (LOX), alcohol dehydrogenase (ADH) and alcohol acyltransferase (AAT). Among them, LOX catalyzes fatty acids to produce C6 aldehydes, ADH reduces them to C6 alcohols, and AAT further produces esters with fruity aroma (Wu et al., 2022). In addition, some aromatic components such as terpenes and phenylpropanoids are catalyzed by terpene synthase (TPS) and phenylalanine aminolyase, and also play a certain role in flavor expression (Fan et al., 2022). 2.3 Molecular regulatory mechanism of golden pitaya flavor formation During the formation of golden pitaya flavor, there are significant interactions between metabolic pathways such as sugar, acid, and aroma. For example, sugar and organic acids share intermediates (such as PEP) in carbon metabolism, and the accumulation of the two is competitive (Miao et al., 2024). Volatile organic compounds (VOCs), such as esters, terpenes, aldehydes, alcohols, and ketones, are the main contributors to fruit aroma and flavor. These substances are produced through multiple biosynthetic pathways, especially terpenoids, phenylalanine, and fatty acid pathways (Xu et al., 2022; Lu et al., 2024). Key enzyme-encoding genes and transcription factors (TFs) are essential for regulating the synthesis of flavor compounds. For example, NAC transcription factors (such as PpNAC1 and PpNAC5) activate genes involved in ester formation, sugar accumulation, and organic acid degradation, directly affecting aroma and taste. Epigenetic modifications (such as removal of repressive histone marks) and post-transcriptional mechanisms (such as alternative splicing and mRNA methylation) further fine-tune the expression of flavor-related genes during fruit ripening (Cao et al., 2021; Zhang et al., 2023). The expression levels of these regulatory factors and their interactions with target metabolic genes constitute a complex flavor metabolic regulatory network. By identifying and intervening in these core regulatory nodes, it is expected to achieve precise regulation and optimization of the flavor components of golden pitaya. 3 Target Gene Selection for Flavor Improvement of Golden Pitaya 3.1 Genes related to sugar metabolism Increasing the sugar content of fruit is a direct way to enhance sweetness. The genes that affect the sugar content of fruit mainly include: enzymes and regulatory factors that control the decomposition and transport of sucrose, and source-sink signaling pathway genes that affect the distribution of photosynthetic products (Vimolmangkang et al., 2016; Fang et al., 2023). In tomatoes, several effective gene editing targets for increasing the sugar content of fruit have been identified. For example, the cell wall acid invertase inhibitor protein SlINVINH1 is a negative regulator that inhibits the decomposition of sucrose by cell wall invertase (CWIN). Wang et al. (2021) used CRISPR/Cas9 to knock out SlINVINH1, thereby increasing the activity of invertase and significantly increasing
RkJQdWJsaXNoZXIy MjQ4ODYzNA==