Drought, as a major threat to global agricultural production and food security, severely constrains crop yield primarily due to the widespread physiological damage and growth inhibition it induces in plants [1]. During the early stages of drought stress, plants are primarily affected by osmotic stress. It subsequently impairs the normal opening and closing of stomata and the transport of photosynthetic products, significantly inhibiting photosynthetic efficiency [2]. As drought stress intensifies, plants undergo significant morphological and physiological changes. Morphologically, leaf area decreases, leaves thicken, and mesophyll tissue becomes more compact. Root systems become more developed, with increased root length, surface area, and volume, leading to a marked increase in root-to-shoot ratio. Concurrently, biomass accumulation declines, leaf number and plant height decrease, and leaf senescence and shedding may occur [3]. Physiologically, drought stress disrupts the balance between reactive oxygen species (ROS) production and scavenging in plants, leading to excessive ROS accumulation [4]. This excess ROS triggers membrane lipid peroxidation, damaging cell membrane structures and impairing the normal functions of chloroplasts and mitochondria, thereby affecting photosynthesis and respiration [5]. Under prolonged drought stress, plant growth and development are severely inhibited, potentially resulting in death [6].

Plants have evolved a highly coordinated adaptive network, which integrates key components such as energy metabolism regulation, redox balance, and signal transduction pathways [7]. Within this network, the dynamic adjustment of photosynthesis and carbon metabolism forms the core of energy supply. In response to drought-induced suppression of photosystem II core protein D1 turnover and the activity of RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) activase, plants maintain energy homeostasis and osmotic balance by optimizing light energy utilization, regulating stomatal conductance, and redistributing carbon sources (e.g., increasing soluble sugar accumulation) [8], [9]. Synergistically, mitochondrial respiration undergoes remodeling, where key proteins like the alternative oxidase play a pivotal role in maintaining energy output, mitigating mitochondrial ROS bursts, and transmitting stress signals by regulating electron transport [10]. The combined effects of energy metabolism adjustments and drought stress intensify oxidative stress, prompting plants to activate robust ROS scavenging mechanisms [11]. ROS scavenging mechanisms rely not only on enzymatic systems like superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), but also involve numerous secondary metabolites—flavonoids, phenolic acids, and terpenoids—to provide complementary non-enzymatic antioxidant defenses and multi-layered protection [12], [13]. Plant hormone signaling system, centered on abscisic acid (ABA) pathway [14], plays an important role in drought responses. ABA signaling is perceived by specific receptors such as PYR/PYL, and is rapidly transmitted through a cascade involving PP2C phosphatases and SnRK2.6 kinases like OST1. This triggers rapid stomatal closure to reduce water loss and activates transcription factors such as AREB/ABF, thereby driving the expression of drought-response genes encoding LEA proteins, dehydrogenases, and secondary metabolite synthesis genes [8], [15], [16]. Concurrently, other hormones like ethylene, jasmonic acid, and cytokinins engage in extensive crosstalk to finely regulate photosynthesis, respiration, carbon metabolism, secondary metabolism, and antioxidant processes. Together, they ensure plant survival and adaptive growth under drought stress [17], [18].

Sugar beet (Beta vulgaris L.) is a biennial herbaceous plant belonging to the Amaranthaceae family. As a major source of sugar production, it accounts for approximately 30% of the world's annual sugar output, making it a crop of significant economic importance [19]. Major sugar beet growing regions are frequently subjected to drought stress, causing substantial losses in yield and quality, with far-reaching impacts on the entire sugar industry and related economic sectors [20]. Therefore, investigating the molecular mechanisms underlying sugar beet drought tolerance is crucial for enhancing drought tolerance and developing stress-resilient germplasm resources. Proteomics approaches have played a pivotal role in deciphering sugar beet's drought response mechanisms. Hajheidari et al. pioneered the use of two-dimensional gel electrophoresis (2-DE) coupled with LC-MS/MS to analyze the drought-induced proteome of field-grown sugar beet leaves, identifying 79 differentially abundant proteins(DAPs) including RuBisCO fragments, heat shock proteins (HSPs), and redox regulatory proteins [21]. Wang et al. compared drought-tolerant and sensitive beet varieties using 2-DE and MALDI-TOF MS, revealing significant upregulation of antioxidant enzymes and metabolic proteins in tolerant varieties. This highlights the importance of proteins involved in osmoregulation and redox homeostasis pathways for beet drought tolerance [22]. Schneider et al. further employed LC-MS/MS to analyze protein dynamics during drought and rehydration in sugar beets. They observed sustained high expression of “persistent proteins” post-rehydration, suggesting a protein-level “memory” mechanism that facilitates rapid re-response to stress [23].

The sugar beet M14 line is a diploid sugar beet that carries a monosomic addition of chromosome 9 from the wild white-flowered beet (B. corolliflora Zoss.), developed through distant hybridization. By incorporating genetic resources from the wild species, the M14 line exhibits enhanced salt tolerance (capable of normal growth under 500 mM NaCl stress) compared to major cultivated sugar beet varieties in China (capable of normal growth under 280 mM NaCl stress) [24]. This makes it an exceptionally valuable genetic resource for exploring plant salt tolerance mechanisms.

Our laboratory previously employed proteomics research to identify multiple DAPs from the M14 line under salt stress. Key genes associated with salt tolerance were selected for functional studies, establishing a salt-tolerant gene resource library for the M14 line cultivar [25]. Furthermore, combining proteomics with reverse genetics revealed the salt tolerance mechanisms in the M14 line under salt stress. It achieves salt tolerance primarily through synergistic mechanisms involving osmotic regulation, oxidative defense, and stress signal transduction mediated by cross-talk between phosphorylation and ubiquitination pathways [24], [25], [26], [27]. Notably, both drought and salt stress induce osmotic stress, sharing significant common pathways at the molecular response level. Given that the M14 line has demonstrated highly efficient osmotic regulation and oxidative defense capabilities under salt stress, it is presumed to exhibit strong drought tolerance under drought stress as well.

Building upon our prior research on the molecular mechanisms of salt tolerance of the M14 line, this study marks the first investigation into drought tolerance in the M14 line. Drought tolerance was also evaluated in five major diploid cultivated sugar beet varieties grown in northern China. Results revealed that the M14 line exhibited the strongest drought tolerance, establishing it as an excellent genetic resource for identifying drought-tolerant genes in plants. Using proteomics, we analyzed DAPs in the M14 leaves under drought stress. This enabled the construction of a molecular network map for drought tolerance in the M14 line, identifying key proteins associated with drought resistance. These findings provide a theoretical basis for elucidating the regulatory mechanisms of beet drought tolerance, and facilitate developing new drought-tolerant beet varieties.