Transcriptome Analyses Reveal the Mechanism of Changes in the Sugar Constituents of Jujube Fruits under Saline-Alkali Stress

Saline-alkali stress is an important environmental factor affecting the growth and development of plants. Plants affected by saline-alkali stress can mitigate the damage by regulating the content of osmoregulatory substances such as soluble sugars. Elucidating the regulatory mechanism of the changes in sugar fractions in jujube fruits under saline-alkali stress is crucial for the development of the jujube fruit industry in saline areas. In this study, we investigated the effects of saline-alkali stress on the development and sugar contents of jujube fruits by subjecting jujube trees to low- and high-saline-alkali stress treatments. The result showed that low saline-alkali stress increased the content of each sugar component and total sugar, whereas high saline-alkali stress suppressed their contents. In the early developmental stage, the fruit mainly accumulated fructose and glucose, whereas in the late stage, it accumulated mainly sucrose. We screened various genes, namely trehalose 6-phosphate phosphatase gene (LOC107418410), beta-amylase gene (LOC107428855), beta-glucosidase gene (LOC107418468), sucrose synthase gene (LOC107416188), and beta-amylase gene (LOC107430415, LOC107406235), all of which were highly correlated with sucrose content in saline-alkali stress, indicating that the starch and sucrose metabolic pathways of jujube fruit are the key pathways regulating sugar accumulation in response to saline-alkali stress. To summarize, this study provides a system-level perspective on the dynamic transcriptional regulation of jujube fruits under saline-alkali stress. Additionally, the study preliminarily screened key differentially expressed genes that affect sugar accumulation in response to saline-alkali stress, providing a theoretical basis for the scientific regulation of jujube fruit quality.