International Journal of Horticulture, 2025, Vol.15, No.5, 234-241 http://hortherbpublisher.com/index.php/ijh 235 softening can delay early softening of the fruit and improve storage stability; study on sugar deposition can maximize quality of flavor and nutrition; studies on antioxidant metabolism can improve antioxidant capacity of the fruit and extend shelf life. Thorough understanding of these control mechanisms will unveil valuable targets for molecular breeding and gene editing, enable new storage-resistant and high-quality varieties to be bred, and optimize post-harvest management practices to improve the industrial sustainability and market competitiveness of Pitayas. 2 Genetic Regulation of Pitaya Fruit Softening 2.1 Role of cell wall degradation in fruit softening Breakdown of the cell wall is a chief operation for Pitayas softening, which is breakdown of complicated carbohydrates into simpler forms. This breakdown is promoted by a variety of cell wall alteration enzymes, modifying cell wall organization, thus fruit tissue softening. The cell wall degradation is a synergistic process involving the combined action of a variety of enzymes such as pectinase, cellulase and hemicellulase, which ultimately result in texture modification in fruit ripening (Chen et al., 2022). 2.2 Function of key cell wall-modifying enzymes Some of the principal enzymes responsible for fruit softening include pectin methyl esterase (PME), polygalacturonidase (PG), and cellulase (CEL). Santos et al. (2019) showed that these enzymes play a crucial role in the degradation of the main components of the primary cell wall such as pectin, cellulose and hemicellulose. Its activity is stringently regulated during fruit softening during fruit ripening so that the fruit becomes softened at the appropriate time, thereby improving quality palatable and seed dispersal. These genes' expression is generally enhanced during the softening of the fruit, which indicates the function of the enzymes in softening. 2.3 Role of ethylene and other hormones in softening regulation One of the key hormones for fruit softening and ripening of several fleshy fruits, including Pitaya, is ethylene. Ethylene, as a molecule of ethylene, can induce the expression of cell wall-breakdown-related genes and related mature genes. In addition to ethylene, abscisic acid (ABA) and auxin also play a role in fruit ripening regulation. These hormones convey complex network messages to control the duration and quantity of fruit softening to the desired level, hence optimizing fruit quality and shelf life (Bianchetti et al., 2024). 2.4 Softening-related genes and their signaling networks Fruit softening is regulated by a cascade of hormone- and environment-sensitive gene networks. WRKY, Dof and MYB transcription factors were shown to be critical regulators of gene expression during fruit ripening. For example, WRKY transcription factor HpWRKY3 regulates sugar metabolism gene expression, indirectly affecting osmotic balance during fruit softening (Li et al., 2022). Apart from that, Liu et al. (2021) found that Dof transcription factors (such as HpDof1.7 and HpDof5.4) are involved in the transcriptional activation of sugar metabolism genes, which subsequently affect the process of fruit softening. The transcription factors belong to a complex signaling regulation system where hormone signals and developmental signals are integrated to refine the timing and process of fruit softening. 3 Regulatory Mechanisms of Sugar Accumulation in Pitaya Fruit 3.1 Changes in sugar content and their impact on fruit quality The sugar content is an essential parameter that represents the quality of the fruit and affects the taste and consumers' preferences. Glucose prevails in Pitaya, followed by sucrose and fructose, and these all have significant functions to determine the sweetness of the fruit as well as overall flavor profiles (Li et al., 2024). During fruit ripening, the content of soluble sugar is significantly increased, which improves the sweetness and quality of the fruit for sale. Sugar deposition is closely linked to the expression of some genes and the activities of sugar metabolic enzymes, and they are critical to the formation of high-quality characteristics of the fruit (Wu et al., 2019).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==