Low temperature and cold damage seriously hinder the growth, development, and morphogenesis of cotton seedlings. However, the response mechanism of cotton seedlings under cold stress still lacks research. In this study, transcriptome sequencing, gas exchange parameters, and rapid chlorophyll fluorescence parameters were analyzed in leaves of cold-tolerant upland cotton variety “ZM36” under different temperature stress [25°C (T25, CK), 15°C (T15), 10°C (T10), and 4°C (T4)]. The results showed that the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), PSII potential maximum photochemical efficiency (Fv/Fm), and performance index (PIabs) of cotton leaves significantly decreased, and the intercellular CO₂ concentration (Ci) and Fo/Fm significantly increased under cold stress. The transcriptome sequencing analysis showed that a total of 13,183 DEGs were involved in the response of cotton seedlings at each temperature point (T25, T15, T10, and T4), mainly involving five metabolic pathways—the phosphatidylinositol signaling system, photosynthesis, photosynthesis antenna protein, carbon fixation in photosynthetic organisms, and carotenoid synthesis. The 1,119 transcription factors were discovered among all the DEGs. These transcription factors involve 59 families, of which 15.8% of genes in the NAC family are upregulated. Through network regulatory analysis, the five candidate genes GhUVR8 (GH_A05G3668), GhPLATZ (GH_A09G2161), GhFAD4-1 (GH_A01G0758), GhNFYA1 (GH_A02G1336), and GhFAD4-2 (GH_D01G0766) were identified in response to cold stress. Furthermore, suppressing the expression level of GhPLATZ by virus-induced gene silencing led to the reduction of low temperature resistance, implying GhPLATZ as a positive regulator of low temperature tolerance. The findings of the study revealed a piece of the complex response mechanism of the cold-tolerant variety “ZM36” to different cold stresses and excavated key candidate genes for low temperature response, which provided support for accelerating the selection and breeding of cotton varieties with low temperature tolerance.

In China, cotton is a significant cash crop, and cold stress negatively impacts the crop’s development, production, and quality formation. Recent studies have shown that melatonin (MT) can alleviate the damage to plants under cold stress and promote good growth and development. In this study, the morphological and physiological changes induced by exogenous melatonin pretreatment on ‘Xinluzao 33’ cotton seedlings under cold stress were examined to investigate its defensive effects. The results showed that 100 μM MT pretreatment improved the cold resistance of cotton most significantly. It also improved the wilting state of cotton under cold stress, greatly increased the photosynthetic rate (Pn), stomatal conductance (Gs), maximum photochemical efficiency (Fv/Fm), and photosynthetic performance index (PIabs) by 116.92%, 47.16%, 32.30%, and 50.22%, respectively, and mitigated the adverse effects of low-temperature. In addition, MT supplementation substantially reduced the accumulation of superoxide anion (O₂^•−) and hydrogen peroxide (H₂O₂) by 14.5% and 45.49%, respectively, in cold-stressed cotton leaves by modulating the antioxidant system, thereby mitigating oxidative damage. Furthermore, MT pretreatment increased the endogenous melatonin content (23.80%) and flavonoid content (21.44%) and considerably induced the expression of biosynthesis enzyme-related genes. The above results indicate that exogenous melatonin improves the low-temperature resistance of cotton seedlings by regulating photosynthetic performance, antioxidant enzyme activity, antioxidant content, endogenous melatonin and flavonoid content, and the expression levels of genes related to their synthesis.

With-No-Lysine (WNK) kinases are a subfamily of serine/threonine protein kinases. WNKs are involved in plant abiotic stress response and circadian rhythms. However, members of the WNK subfamily and their responses to abiotic and biotic stresses in Gossypium hirsutum have not been reported. In this study, 26 GhWNKs were identified in G. hirsutum. The gene structure, conserved motifs, and upstream open reading frames (uORFs) of GhWNKs were identified. Moreover, GhWNKs regulation is predicted to be regulated by cis-acting elements, such as ABA responsive element (ABRE), MBS, and MYC. Furthermore, transcription factors including MIKC_MADS, C2H2, TALE, bZIP, Dof, MYB, bHLH, and HD-ZIP are projected to play a regulatory role in GhWNKs. The expression patterns of GhWNKs under normal conditions and biotic and abiotic stresses were evaluated, and their expression was found to vary. The expression patterns of several GhWNKs were induced by infiltration with Verticillium dahliae, suggesting that several GhWNKs may play important roles in the response of cotton to V. dahliae. Interestingly, a homoeologous expression bias within the GhWNKs was uncovered in upland cotton. Homoeologous expression bias within GhWNKs provides a framework to assist researchers and breeders in developing strategies to improve cotton traits by manipulating individual or multiple homeologs.

Background: The gene family of myelomatosis (MYC), serving as a transcription factor in the jasmonate (JA) signaling pathway, displays a significant level of conservation across diverse animal and plant species. Cotton is the most widely used plant for fiber production. Nevertheless, there is a paucity of literature reporting on the members of MYCs and how they respond to biotic stresses in cotton. Methods: Bioinformatics analysis was used to mine the MYC gene family in cotton based on InterPro, cottongen, etc. Results: The gene structure, conserved motifs, and upstream open reading frames of 32 GhMYCs in Gossypium hirsutum were identified. Moreover, it was anticipated that the GT1-motif is the most abundant in GhMYCs, indicating that the GT1-motif plays a significant role in light-responsive GhMYCs. The expression patterns of GhMYCs under biotic stresses including V. dahliae and Aphid gossypii were evaluated, suggesting that GhMYCs in class-1 and -3 GhMYCs, which function as negative regulators, are involved in resistance to verticillium wilt and aphids. The class-3 GhMYCs genes were found to be mostly expressed in female tissues. Interestingly, it was also determined that the homeologous expression bias within GhMYCs in cotton was uncovered, and results showed that the gene expression of class-1A and class-2 GhMYCs in the Dt sub-genome may have a direct impact on gene function. Conclusions: This study provides a research direction for researchers and breeders to enhance cotton traits through manipulating individual or multiple homeologs, which laid a foundation for further study of the molecular characteristics and biological functions of GhMYC gene.

Low-temperature stress severely restricts cotton seed germination and seedling establishment, especially in early spring. Ascorbic acid (AsA) priming is a promising strategy to enhance stress tolerance, yet its mechanisms in cotton remain unclear. This study examined the effects of AsA priming on seed germination at 15 °C. Seeds were treated with 0, 25, 50, or 100 mg/L AsA for 3, 6, 12, or 24 h. Results showed that 50 mg/L AsA for 24 h significantly improved germination potential, rate, index, and promptness index (p < 0.05). Compared with water-primed seeds, AsA-primed seeds exhibited greater radicle length (+17.67%) and fresh weight (+136.26%) under chilling stress. This treatment markedly increased antioxidant enzyme activities, including POD (+196.74%), SOD (+43.81%), and CAT (+49.43%), while also promoting the accumulation of Ascorbate–Glutathione cycle-related enzymes and metabolites, thereby reinforcing the antioxidant defense system. Multidimensional statistical analyses further indicated that AsA enhanced root growth by stimulating antioxidant defenses while inducing a trade-off that slightly reduced fresh weight, suggesting a balance between growth and oxidative protection. Overall, AsA priming improves cotton seed cold tolerance by activating enzymatic and non-enzymatic antioxidant systems and mediating a growth–defense trade-off, underscoring its potential as an effective priming agent for early sowing under low-temperature stress.

Purpose: Gibberellins (GAs) are key phytohormones that regulate plant growth, development, and responses to environmental stress, and their metabolism is mediated by 2-oxoglutarate-dependent dioxygenases (2OGDs). Cotton (Gossypium spp.) is a polyploid crop with a complex genome; however, the evolutionary characteristics and stress-responsive regulation of GA-related 2OGDs remain poorly understood. This study aimed to systematically investigate the evolution, expression patterns, and stress-associated regulation of the cotton 2OGD multigene family, with particular emphasis on GA-related members. Methods: 2OGD genes were identified genome-wide in four Gossypium species and Arabidopsis thaliana. Phylogenetic relationships, gene structures, conserved motifs, cis-acting regulatory elements, and synteny were analyzed. Transcriptomic data from multiple tissues and developmental stages, together with time-course RNA-seq under salt stress, were examined. Transcriptome–metabolome association analysis, endogenous GA quantification, and predicted protein–protein interaction analysis were conducted. Results: A total of 583 2OGD genes were identified and classified into three major classes, including a Class C group comprising GA2ox, GA3ox, and GA20ox genes. Polyploidization-associated duplication contributed to the expansion of the 2OGD family, and most duplicated gene pairs exhibited signatures of purifying selection. GA-related 2OGDs displayed conserved motif compositions with variation in cis-acting elements. Promoter analysis identified abundant hormone-responsive, stress-responsive, and growth-related cis-elements, suggesting complex regulatory control of GA-related 2OGDs in cotton. Under salt stress, GhGA2OX1 and GhGA20OX2 were upregulated, whereas GhGA3OX1 was downregulated, accompanied by reduced endogenous GA levels. Conclusions: GA-related 2OGDs in cotton are transcriptionally responsive to salt stress and are associated with changes in GA metabolism, providing a basis for future functional studies.