Recently, the research group of Zhao Deying, pomaceous fruits cultivation and physiological innovation team at the Institute of Pomology of Chinese Academy of Agricultural Sciences, discovered that the galactinol synthase encoding gene MdGolS5  enhances the cold resistance of apples by regulating the accumulation of raffinose family oligosaccharides. The results were published in JCR Q1 journal ‘Plant Physiology and Biochemistry’ (IF: 6.1 ).

In a previous study, the cold-resistant ‘Hanfu’ and cold-sensitive ‘Naganofuji 2’ apple varieties at various dormancy stages during winter were analyzed using transcriptome and metabolome techniques. We found that the galactinol synthase (GolS) encoding gene MdGolS5 (MdoChr04g0483) in the raffinose family oligosaccharides metabolic pathway was up-regulated at -15 °C, leading to the accumulation of a large amount of galactinol at low temperatures. However, despite this finding indicating the potential role of galactinol in the low-temperature response of apples, there are few reports on the direct effects of exogenous galactinol spraying on the cold resistance of apples.

Therefore, this study first focused on the effect of exogenous galactinol treatment on the one-year-old branches of apple, and found that exogenous spraying of 100 mg·mL⁻¹galactinol could effectively alleviate the damage of low temperature stress to apple saplings. To further explore the cold-resistance mechanisms of GolS in apples, ‘Orin’ apple callus and tobacco plants overexpressing MdGolS5 were constructed and exposed to low-temperature stress. Both grew well under low-temperature stress, and their relative conductivity was significantly lower than that of their respective wild types. Moreover, the malondialdehyde, superoxide anion, and hydrogen peroxide content in MdGolS5-overexpressing tobacco was significantly lower than that in the wild type under -2°C freezing treatment, while the activities of antioxidant enzymes such as superoxide dismutase and GolS were significantly higher, and a large amount of proline, galactinol, and raffinose were accumulated. The expression patterns of cold-responsive genes under freezing low-temperature conditions were analyzed, and the expression levels of MdCBF1, MdCBF2, MdCBF3, and MdCOR47 were found to be significantly increased in the transgenic tobacco. In conclusion, our study provides a new perspective on the role of  raffinose family oligosaccharides synthesis and metabolism in cold adaptation in apples.

Figure 1 ROS metabolism in MdGolS5-overexpressing tobacco. (A) Diaminobenzidine and nitroblue tetrazolium staining of tobacco leaves; (B) ROS accumulation and antioxidant enzyme activity.

Figure 2 Schematic diagram of the mode of action of galactinol in enhancing apple tolerance to cold stress. Red arrows indicate activation.

Professor Zhao Deying of Institute of Pomology is the corresponding author of the paper, and Dr. Xu Gongxun is the first author. This work was supported by the Fundamental Research Funds for

Central Nonprofit Scientific Institution (1610182024006), the earmarked fund for CARS (CARS-27), the Applied Basic Research Project of Science and Technology Department of Liaoning Province (2023JH2/101300131), the Shenyang Science and Technology Plan Seed Industry Innovation Special (22-318-2-03), the Scientific Research Funding Project of Liaoning Province (LJKMZ20221026) and the Innovation Project of the Chinese Academy of Agricultural Sciences (CAAS-ASTIP).

Original title: Galactinol synthase gene 5 (MdGolS5) enhances the cold resistance of apples by promoting raffinose family oligosaccharide accumulation

DOI: https://doi.org/10.1016/j.plaphy.2024.109416

By: Xu Gongxun

(xugongxun@caas.cn)