Ginger (Zingiber officinale Roscoe) is a versatile vegetable crop with a savory flavor belonging to the ginger family. Ginger benefits from its beneficial properties such as pungent aroma and pharmacological activity and is used as a food, spice, supplement and flavoring as well as a traditional medicine (Kiyama, 2020). It is one of China’s key export-earning vegetables. Ginger has been used as a digestive and anti-inflammatory medicine by the Chinese for at least 2,500 years. Ginger is an important crop in Shandong Province, China (Liu et al., 2020). The rhizome, as the main product organ of ginger, is an underground organ along with the root and is influenced by the soil environment. Ginger has the characteristics of continuous cultivation, which, together with the large number of fertilizers applied by farmers during the cultivation process, can lead to secondary salinization in the main ginger-producing areas, which echoes the following situation.

Salinization of soil and freshwater resources by natural processes and human activities has become a growing problem affecting environmental services and socio-economic relations (Ondrasek et al., 2022). Due to the capillary action of groundwater, the soluble salt in the soil will accumulate on the surface with the increase of evaporation. High salt content will lead to different degrees of salinization (Feng et al., 2019). By 2050, salinization is anticipated to have varied effects on nearly half of agricultural land (Kumar et al., 2020). China’s arable land resources are scarce, less than 40% of the world average, and with a large population, the arable land per capita is only 0.092 hectares (Zhang and Wang, 2021). By analyzing the soil in the main ginger-producing area of Shandong province, we found that the average salt content ranged from 0.22% to 0.36%, and the highest salt content was up to 0.5%. This has a noteworthy effect on the number of gingers grown and the cost-effectiveness of land utilization. There are now two primary techniques for reducing soil salinity: trying to add chemicals and generating salt-tolerant plant types via biotechnology. In contrast, the former can lead to secondary salinization and is expensive. Therefore, it is very important to understand the mechanism of plant salt tolerance by cultivating salt-tolerant plants (Hao et al., 2021).

Some scholars have discovered via thorough comparison studies that the relative importance of fresh weight and electrolyte leakage is the clear and concise marker to evaluate the salt stress tolerance of Chinese cabbage (Li et al., 2021). Salt-induced osmotic stress in tomato exhibited lower relative water content, where higher Na/K ratios indicated ionic toxicity (Zhou et al., 2022). Malondialdehyde, endogenous proline and electrolyte leakage, antioxidant defense systems, and sodium ion content were all found to increase significantly after NaCl stress (Sofy et al., 2020). Salt stress caused an increase in antioxidant enzyme activities such as ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and proline content in Aloe vera compared to the control (Kavian et al., 2022). Several DEGs enriched in plant signal transduction pathways were highly expressed in oilseed rape seedlings under salt stress (Wang et al., 2022b). Therefore, in this study, we selected the ginger variety ‘Shannong No.1’ as the experimental material to study the changes in the overall osmoregulatory system and reactive oxygen metabolism of ginger during the more sensitive seedling stage (80 d). The possible genes and pathways connected to the stress-induced response were explored in this work, which employed RNA sequencing to investigate changes in the expression of several genes in ginger seedlings under salt stress. The breeding of salt-tolerant cultivars and the appropriate use of land resources both benefit tremendously from this work.

Growth inhibition, rapid development, and aging are prominent signs of salt stress damage since prolonged exposure may cause plants to die (Acosta-Motos et al., 2017). Growth inhibition is a major impairment leading to other symptoms and may also lead to programmed cell death under severe salinity shocks (Jouyban, 2012). Tanveer et al. found that salt pressure forced tomato seeds to reduce germination time by 27.6% and salt tolerance by 27.6%. Seedling length and viability decreased by 24.33% (Tanveer et al., 2020). Researchers noted that the initial drop in development was brought on by the osmosis of salt outside the root, but the following reduction in growth was brought on by the failure to keep the salt from reaching dangerous levels in the carrying leaves (Geilfus, 2018). According to Mathias J, greater osmotic content may have contributed to the relative water content of pepper leaves being higher in salt-tolerant types than salt-sensitive ones (Hand et al., 2017). After salt stress, tomatoes experience lipid peroxidation salt stress, which Siddiqui hypothesized may be generated by the buildup of MDA in the membrane, which is driven by ROS (Siddiqui et al., 2017). Lipid peroxidation is a frequently used indicator of membrane damage brought on by stress (Sekmen et al., 2012). In this case, salt-tolerant varieties were able to reduce lipid peroxidation levels by reducing MDA content. Mahmoud et al. showed that similar to Lipid peroxidation, H₂O₂ content in the leaves of cultivars increased with varying degrees under salt stress (Akrami and Arzani, 2018). Interestingly, in our study, after salt stress treatment of ginger, the MDA content level of each part was positively correlated with H₂O₂ content and superoxide anion production rate, indicating that the level of lipid peroxidation was increased. It is worth noting that the proline content of each part also showed an upward trend to varying degrees.

Recent studies have shown that antioxidant enzyme activity is induced to increase under salt stress, suggesting that resistance to it is protective against stress responses (Cai et al., 2021). Susana discovered that silicon controlled the activities of antioxidant enzymes and nitrogen metabolism to mitigate the negative effects of salt on sunflower plants (Conceição et al., 2019). The findings indicated a positive association between SOD, CAT, and POX activity in tall fescue leaves as an increase in SOD activity was followed by increases in CAT and POX activity, which reduced the buildup of H₂O₂ caused by abiotic stress (Fu et al., 2015). Wang mentioned that melatonin’s impact on cucumber seedlings under salt stress is connected to the formation of hydrogen peroxide (Zhang et al., 2020). According to this research, salt stress dramatically enhanced the levels of SOD, POD, CAT, and APX in different tissues and sections of ginger during the seedling stage. Combined with the ROS products discussed and analyzed above, it is speculated that this phenomenon may be the stress response of ginger under salt stress. A potassium deficit should be noted as a potential cause of growth limitation. The most hazardous sodium-potassium ratio is high. In order to sustain enough potassium nutrition under salt stress, plants must thus use a highly selective and high-affinity potassium absorption mechanism (Jouyban and Sciences, 2012). It’s interesting how this matches the findings of this research. After salt stress, it was discovered that the Na⁺/K⁺ ratio dramatically rose, particularly in the ginger root. Kongake et al. found that Na⁺ content in salt-sensitive rice roots directly increased with increasing NaCl concentration, resulting in decreased plant water content and growth inhibition, presumably resulting in membrane damage due to Na⁺/K⁺ and Na⁺ toxicity (Siringam et al., 2011). Zeeshan found that barley and wheat varieties were more salt-tolerant by making the sodium-to-potassium ratio more balanced and by increasing ROS scavenging enzyme activity(Zeeshan et al., 2020).

DREB is a TFS that regulates the expression of various stress response genes in plants. In this study, the gene 121982991 in Ginger Root was closely related to the biological function of DREB after salt stress. Some studies have shown that the DREB gene BADBL1, derived from the desiccation-tolerant moss, makes transgenic Arabidopsis thaliana tolerant to osmotic pressure and salt stress. This may be accomplished by raising the activity of its antioxidant enzymes, controlling the expression of stress-related genes in plants, and modifying the lignin’s production (Liang et al., 2021). Additionally, it has been shown that the functional homolog GHDREB1 may enhance the freezing, salt, and osmotic tolerance of transgenic Arabidopsis thaliana (Lata and Prasad, 2011). The APETALA2/Ethylene Responsive Factor Transcription Factor family is one of the mechanisms mentioned by Sameer. This family regulates salt tolerance by binding to upstream the DNA of genes that function specifically in the salt-tolerant pathway. As a result, the DREB protein increased the expression of these salt-tolerant genes (Hassan et al., 2022). In addition, we discovered that the biological function of MYB under salt stress was tightly connected to the ginger root gene 122051202. Many of the MYB proteins’ downstream targets have been discovered, and these proteins help plants tolerate salt. IBMYB308, a sweet potato isozyme, was shown in Wang’s work to enhance transgenic tobacco’s salt tolerance (Wang et al., 2022a). According to Li’s work, Fvmyb82 from strawberries may be crucial for regulating downstream-related genes in Arabidopsis during salt and cold stress (Li et al., 2022). Through an ABA-dependent mechanism, it was discovered that the maize MYB transcription factor ZMMYB3R increases tolerance to salt and drought stress (Wu et al., 2019). The response to abiotic stressors is significantly influenced by the Mitogen-Activated Protein Kinase (MAPK) cascade. The biological activity of MAPK following salt stress was discovered to be strongly connected to the ginger leaf gene 122020538, according to this research. Ying et al. discovered that GHCIPK6A’s function in scavenging ROS and MAPK signaling pathways was responsible for the increased salt tolerance of transgenic upland cotton (Su et al., 2020). According to Hoang et al., the MAP kinase MPK6 is activated and interacts with MYB41, increasing salt tolerance in Arabidopsis thaliana. This suggests that MAP kinases, which function as signal sensors and transmit osmotic pressure signals to the appropriate effectors, aid plant cells in becoming acclimated to high salt concentrations (Hoang et al., 2012). By raising the expression of stress-related genes and the activity of antioxidant enzymes under salt stress, FTMAPK1 improved the stress resistance in Yao’s research (Yao et al., 2022). The grape-isolated protein VVMAPK9, when overexpressed in Arabidopsis thaliana, significantly improved the plant’s ability to withstand salt stress. In addition, overexpressed VVMAPK9 in grape Calli improved the Calli’s capacity to scavenge reactive oxygen species, which further improved the salt-resistant mechanism (Ji et al., 2022).

Ginger uses the rootstock as its main edible organ, so the soil environment is particularly important and sensitive to its underground organs. Regardless of where ginger is grown globally or in China, soil salinity problems have a significant impact on plant growth and development. The results of this study showed that salt stress inhibited ginger growth with increased osmoregulatory substances, increased reactive oxygen species, increased sodium ion content, and enhanced antioxidant enzyme activity. Analysis of the indicators of each tissue part revealed that roots and leaves were the most significantly changed parts. After analyzing the transcriptional differences between roots and leaves by RNA-seq, it was found that they jointly initiated MAPK signaling pathway in response to salt stress. This work effectively identifies the physiological and molecular responses of ginger to salt stress during the seedling stage. For future research directions, experimental designs to assist in mitigation can be carried out in terms of both altered inter-root environment and foliar spraying.

The original contributions presented in the study are publicly available. This data can be found here: NCBI, PRJNA898683.

ML and KX conceived the experiments. ML and BC performed the experiments. ML and ZC analyzed the data. ML, YL, ZC, and KX wrote and revised the manuscript. All authors contributed to the article and approved the submitted version.