Drought severely impacts the growth of cotton, and the application of plant biostimulants offers an effective approach to enhancing crop drought tolerance. γ-Poly-glutamic acid (γ-PGA) is a novel and environmentally friendly biostimulant, but its functions and mechanisms in responding to drought stress in cotton are still unclear. This study aims to elucidate the role of the plant biostimulant γ-PGA in the response of cotton to drought stress. Cotton seedlings treated with exogenous γ-PGA and a control group were subjected to drought conditions, and phenotypic observations along with measurements of relevant physiological indicators were conducted. The results showed that the activities of superoxide dismutase (SOD) and peroxidase (POD), as well as the proline (PRO) content in the leaves of γ-PGA-treated cotton, were higher than those in the control group, while malondialdehyde (MDA) content was lower. This indicates that exogenous application of γ-PGA can effectively enhance cotton’s tolerance to drought stress. Subsequently, transcriptome sequencing was performed on the leaves of cotton plants under drought stress in both the γ-PGA-treated and control groups. The results revealed that γ-PGA treatment led to the upregulation of 1,658 genes and the downregulation of 589 genes. Among these differentially expressed genes (DEGs), 233 were transcription factors, suggesting that γ-PGA participates in the cotton drought stress response by regulating the expression of numerous transcription factors. KEGG analysis showed that DEGs were primarily enriched in plant hormone signaling pathways (a total of 103 DEGs). Further analysis revealed that γ-PGA promotes the expression of genes related to ethylene (ETH), Brassinosteroids (BR) and abscisic acid (ABA) hormone signal transduction, indicating that it can enhance cotton’s tolerance to drought stress by regulating the signal transduction of these hormones. This study elucidates the effects of exogenous γ-PGA on drought resistance in cotton, as well as the molecular mechanisms underlying this resistance. The findings provide a theoretical foundation for the future application of γ-PGA to enhance drought tolerance in cotton.

Background: The COBRA-like (COBL) gene family is a crucial glycosylphosphatidylinositol (GPI)-anchored proteins that participate in various biological processes in plants by regulating the arrangement of cell wall microfibrils. While the functions of COBL genes have been analyzed in several plant species, their roles in cotton’s response to abiotic stress remain unexplored. Results: This study identified and characterized the COBL gene family in Gossypium hirsutum, revealing a total of 39 COBL family members classified into five subgroups. Transcriptome analysis indicated that the transcription levels of several GhCOBL genes were upregulated following PEG treatment, with GhCOBL22 being significantly induced. Further silencing of the GhCOBL22 gene through virus-induced gene silencing (VIGS) technology demonstrated that this gene’s silencing reduced cotton’s drought stress tolerance. Under drought stress conditions, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzymes, along with proline (PRO) content, were lower in GhCOBL22-silenced plants compared to control plants, while the accumulation of malondialdehyde (MDA) was significantly higher. Moreover, silencing the GhCOBL22 gene also led to reductions in the levels of cellulose, hemicellulose, and lignin content in cotton leaves. Conclusion: A systematic survey of gene structure, motif composition, and evolutionary relationships of the COBL gene family was conducted in Gossypium hirsutum. Subsequent expression and functional studies indicated that GhCOBL22 plays a significant role in cotton’s drought tolerance. These findings enhance our understanding of the biological functions of the COBL family and highlight the critical role of the GhCOBL22 gene in cotton’s response to drought stress.

Drought stress imposes severe constraints on crop growth and yield. The NAC transcription factors (TF) play a pivotal role in regulating plant stress responses. However, the biological functions and regulatory mechanisms of many cotton NACs have not been explored. In this study, we report the cloning and characterization of GhNAC2-A06, a gene encoding a typical cotton NAC TF. The expression of GhNAC2-A06 was induced by PEG treatment, drought stress, and ABA treatment. Furthermore, we investigated its function using the virus-induced gene silencing (VIGS) method. GhNAC2-A06 silenced plants exhibited a poorer growth status under drought stress conditions compared to the controls. The GhNAC2-A06 silenced cotton plants had a lower leaf relative water and chlorophyll content and a higher MDA content compared to the controls under the drought treatment. The levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzyme activity in the GhNAC2-A06 silenced plants were found to be lower compared to the controls when exposed to drought stress. Additionally, the downregulation of the drought stress-related genes, GhSAP12-D07, GhNCED1-A01, GhLEA14-A11, GhZAT10-D02, GhPROT2-A05, GhABF3-A03, GhABF2-D05, GhSAP3-D07, and GhCPK1-D04, was observed in the GhNAC2-A06 silenced cotton. Together, our research reveals that GhNAC2-A06 plays a role in the reaction of cotton to drought stress by affecting the expression of genes related to drought stress. The data obtained from this study lay the theoretical foundation for further in-depth research on the biological function and regulatory mechanisms of GhNAC2-A06.

As a globally important economic crop, cotton often faces yield and quality limitations due to drought stress. To elucidate drought tolerance mechanisms, this study screened a drought-tolerant variety (64-22-3) and a drought-sensitive variety (Anmian 3, A3) from five drought-resistant and five drought-sensitive materials, respectively. Integrated transcriptomic and metabolomic analyses revealed 7,351 differentially expressed genes (DEGs) in the drought-tolerant variety under drought treatment (5,034 upregulated, 2,317 downregulated), while the drought-sensitive variety exhibited 5,009 DEGs (3,222 upregulated, 1,787 downregulated). Metabolomic profiling identified 169 differentially accumulated metabolites (DAMs) (120 upregulated, 49 downregulated) in 64-22–3 and 173 DAMs (120 upregulated, 53 downregulated) in A3. KEGG enrichment analysis showed that DEGs and DAMs in both varieties were significantly enriched in secondary metabolite biosynthesis, flavonoid biosynthesis, and sesquiterpenoid/triterpenoid biosynthesis. Notably, the drought-tolerant variety displayed specific enrichment in phenylpropanoid biosynthesis, linoleic acid metabolism, and glucosinolate biosynthesis, suggesting their roles in drought adaptation. Weighted gene co-expression network analysis (WGCNA) of 2,064 unique DEGs and 20 key metabolites in the drought-tolerant variety identified blue and turquoise modules as strongly associated with metabolite accumulation, with core hub genes Ghi_D06G05631 and Ghi_A13G12271, which encode TOPLESS-related 1 protein and CIPK6 (CBL-interacting protein kinase 6) separately. Transcription factor (TF) analysis revealed seven high-connectivity TF families (HSF, Golden2-like, SNF2, mTERF, bHLH, C2H2, B3) in the blue module and six TF families (Tify, ARR-B, AUX/IAA, bHLH, Alfin-like, LUG) in the turquoise module, suggesting their coordinated regulation of drought responses. This study systematically elucidates the molecular network underlying cotton’s drought adaptation, providing critical insights for identifying key drought-resistant genes and developing resilient cultivars.

Drought stress is a significant environmental constraint that adversely affects the growth of upland cotton (Gossypium hirsutum) by inducing complex physiological disruptions. Emerging research evidence indicates that melatonin (MT), as a plant growth regulator, is extensively involved in the process of plant stress resistance regulation. This study explored the role of exogenous MT in enhancing drought tolerance in cotton, employing both physiological parameter analysis and transcriptomic profiling to unravel the underlying mechanisms of its stress mitigation effects. The results demonstrated that MT treatment significantly enhanced drought resistance in cotton plants by upregulating leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, elevating proline (PRO) content, and decreasing malondialdehyde (MDA) accumulation, thus confirming its physiological role in alleviating drought stress. Transcriptome analysis revealed that MT specifically modulates the “plant circadian rhythm”, “thiamine metabolism”, and “taurine and hypotaurine metabolism” pathways under drought stress conditions, thereby playing a pivotal role in drought adaptation. Further analysis of the 276 differentially expressed genes (DEGs) specifically modulated by MT under drought stress, combined with co-expression network analysis, identified two MT-specific induced Basic Helix-Loop-Helix (bHLH) family transcription factors (GhPIF8 and GhMYC5, gene IDs: Ghi_A11G05431 and Ghi_D03G05926) as key regulatory candidates in MT-mediated drought tolerance. This study establishes a theoretical framework for understanding the physiological and molecular mechanisms underlying MT-mediated drought tolerance in cotton, while also informing practical applications of MT in cotton agriculture.

SET-domain group histone methyltransferases (SDGs) are known to play crucial roles in plant responses to abiotic stress. However, their specific function in cotton’s response to drought stress has not been well understood. This study conducted a comprehensive analysis of the SDG gene family in Gossypium hirsutum, identifying a total of 82 SDG genes. An evolutionary analysis revealed that the SDG gene family can be divided into eight subgroups. The expression analysis shows that some GhSDG genes are preferentially expressed in specific tissues, indicating their involvement in cotton growth and development. The transcription level of some GhSDG genes is induced by PEG, with GhSDG59 showing significant upregulation upon polyethylene glycol (PEG) treatment. Quantitative polymerase chain reaction (qPCR) analysis showed that the accumulation of transcripts of the GhSDG59 gene was significantly upregulated under drought stress. Further functional studies using virus-induced gene silencing (VIGS) revealed that silencing GhSDG59 reduced cotton tolerance to drought stress. Under drought conditions, the proline content, superoxide dismutase (SOD) and peroxidase (POD) enzyme activities in the GhSDG59-silenced plants were significantly lower than in the control plants, while the malondialdehyde (MDA) content was significantly higher. Transcriptome sequencing showed that silencing the GhSDG59 gene led to significant changes in the expression levels of 1156 genes. The KEGG enrichment analysis revealed that these differentially expressed genes (DEGs) were mainly enriched in the carbon metabolism and the starch and sucrose metabolism pathways. The functional annotation analysis identified known drought-responsive genes, such as ERF, CIPK, and WRKY, among these DEGs. This indicates that GhSDG59 is involved in the drought-stress response in cotton by affecting the expression of genes related to the carbon metabolism and the starch and sucrose metabolism pathways, as well as known drought-responsive genes. This analysis provides valuable information for the functional genomic study of SDGs and highlights potential beneficial genes for genetic improvement and breeding in cotton.