Heat shock protein 90 (HSP90) plays critical roles in plant growth and development, as well as in response to abiotic stresses such as heat and cold. To comprehensively analyze the HSP90 gene family and determine the key HSP90 gene responsive to temperature stress in pumpkin (Cucurbita moschata Duch.), bioinformatics and molecular biology techniques were used in this study. A total of 10 CmoHSP90 genes were identified from the pumpkin genome, encoding amino acids of 567–865, with protein molecular weight of 64.32–97.36 kDa. Based on the phylogenetic analysis, they were classified into four groups. The members in each group contained similar conserved motifs and gene structures. The 10 CmoHSP90 genes were distributed on the 9 chromosomes of C. moschata. Four pairs of segmental duplication genes (CmoHSP90-1/CmoHSP90-10, CmoHSP90-2/CmoHSP90-7, CmoHSP90-3/CmoHSP90-6, and CmoHSP90-4/CmoHSP90-9) were detected. Synteny analysis revealed that 10 C. maxima HSP90 genes and 10 C. moschata HSP90 genes were orthologous genes with 17 syntenic relationships. Promoter analysis detected 23 cis-acting elements including development-, light-, stress-, and hormone-related elements in the promoter regions of pumpkin HSP90 genes. Further analysis showed that the transcript levels of CmoHSP90-3 and CmoHSP90-6 were remarkably up-regulated by heat stress, while CmoHSP90-6 and CmoHSP90-10 were significantly up-regulated by cold stress, suggesting that these HSP90 genes play critical roles in response to temperature stress in pumpkins. The findings will be valuable for understanding the roles of CmoHSP90s in temperature stress response and should provide a foundation for elucidating the function of CmoHSP90s in C. moschata.

Plant endophytic fungi (EF) play crucial roles in enhancing plant resilience to saline conditions. In this study, the halophyte Sesuvium portulacastrum was collected from coastal saline zones adjacent to Hainan Island. Root EF was isolated employing the tissue block method, followed by comprehensive identification and diversity analysis. Salt-tolerant strains were subsequently identified, and pot experiments were conducted to examine their effects on maize growth under saline conditions. A total of 426 cultivable EF isolates were obtained from the roots of S. portulacastrum sampled across 20 distinct locations, categorized into 112 operational taxonomic units (OTUs). Notable differences in EF species distribution were observed across the sampled regions. Screening on potato dextrose agar (PDA) plates supplemented with 0.75 M NaCl revealed that eight EF isolates exhibited significant salt tolerance, with enhanced growth compared to controls. Among these, Fusarium incarnatum strain LG-BZ-9 was shown to not only promote maize growth but also bolster its salt tolerance. Under salt stress conditions, the application of strain LG-BZ-9 led to increased fresh weight, plant height, and leaf chlorophyll content in maize seedlings. Furthermore, a substantial reduction in Na⁺ concentration within maize roots and shoots was observed, accompanied by an increase in K⁺ concentration, resulting in a higher K⁺/Na⁺ ratio. The EF strain isolated in this research effectively enhanced salt tolerance and stimulated maize growth by modulating ion homeostasis. These findings offer a theoretical basis for leveraging beneficial microorganisms to improve crop salt tolerance and augment yields in saline soils.

Watermelon silver mottle virus (WSMoV) and melon yellow spot virus (MYSV) (Tospoviridae, Orthotospovirus) are responsible for silver mottle mosaic and yellow spot symptoms, posing threats to melon (Cucumis melo), watermelon (Citrullus lanatus), and cucumber and leading to significant economic losses in China. Early disease detection and monitoring of these two viruses are necessary for disease management, for which a rapid, reliable, and adaptable diagnostic method is required. In this study, using a droplet digital PCR (ddPCR) method, the conserved region of the nucleocapsid gene (N gene) sequence was detected in WSMoV and MYSV. The probes and primers for WSMoV and MYSV did not detect other relevant cucurbit viruses, and the specificity reached 100%. Although both qPCR and ddPCR exhibited good reproducibility, the reproducibility of ddPCR was better than that of qPCR. The reproducibility of ddPCR was proved to be 100%. Moreover, ddPCR exhibited a good linear correlation with varying concentrations of targets. The detection limits of WSMoV and MYSV in ddPCR were 18 and 9 copies/μL and were approximately 12- and 18-times more than those in qPCR, respectively. Finally, 62 samples collected from the field (including infected melon, watermelon, and weeds) were further evaluated for the presence of WSMoV and MYSV. The field samples exhibited 91.94% and 51.61% positivity rates in ddPCR assays for WSMoV and MYSV, respectively; the rates were higher than those in qPCR (59.68% and 43.39%, respectively). The results indicated that ddPCR has a higher accuracy than qPCR. Therefore, ddPCR could be used in the clinical diagnosis of early infections of WSMoV and MYSV. To the best of our knowledge, this is the first study to establish a ddPCR method for the detection of WSMoV and MYSV. The application of this method for differential detection of MYSV and WSMoV will help in understanding the epidemics caused by these two important viruses and provide important information for the early detection, monitoring, and rapid extermination of infection.

Powdery mildew infection is a significant challenge in butternut squash (Cucurbita moschata) production during winter in Hainan, China. The tropical climate of Hainan promotes powdery mildew infection, resulting in substantial yield losses. By utilizing transcriptome and genome sequencing data, SNPs and potential genes associated with powdery mildew resistance in butternut squash were identified. The analysis of differentially expressed genes (DEGs) following powdery mildew infection revealed several genes involved in resistance, with particular focus on a resistance (R) gene cluster that may be linked to the observed resistance. Two MLO genes in clade V from Cucurbita moschata may not be directly associated with resistance in the two genotypes studied. These findings are expected to contribute to the development of genetic tools for improving powdery mildew resistance in Cucurbita crops, thereby reducing yield losses and enhancing the sustainability of butternut squash production in Hainan and other regions.

Fruit peel cracking significantly reduces the commercial value of melons (Cucumis melo). To elucidate the underlying mechanisms of peel cracking, we conducted integrated investigations including morphological, physiological, metabolomic and transcriptomic analyses of cracked and non-cracked peels from the crack-resistant ‘Xizhoumi 17’ and crack-susceptible ‘Xizhoumi 25’ cultivars. The parenchyma cells in ‘Xizhoumi 17’ exhibited a compact and well-organized arrangement, whereas those in ‘Xizhoumi 25’ displayed a loosely packed and disordered structure. Notably, cracked peels exhibited significantly higher levels of water-soluble pectin and lignin, along with increased cellulase, polygalacturonase, catalase, superoxide dismutase, and peroxidase activities. In contrast, protopectin, cellulose, and hemicellulose contents, as well as polyphenol oxidase activity, were markedly reduced compared to non-cracked peels. Metabolomic analysis revealed that the phenylpropanoid biosynthesis pathway is positively correlated with the progression of peel cracking. RNA-seq analysis revealed 119 and 82 differentially expressed genes associated with cell wall metabolism and lignin biosynthesis pathways, respectively. Collectively, these findings underscore the involvement of genes related to cell wall synthesis and degradation, as well as lignin synthesis, in modulating peel cracking through alterations in cell wall composition and structural stability, thereby offering practical implications for reducing melon peel cracking incidence via targeted molecular breeding of key genes regulating cell wall composition and the phenylpropanoid pathway.

Lignin constitutes a fundamental component of plant defense mechanisms against environmental stressors. 4-coumarate 3-hydroxylase (C3H) serves as a pivotal enzyme in lignin biosynthesis. However, its role in the halophyte Sesuvium portulacastrum remains uncharacterized. In this study, the SpC3H gene was cloned, and subsequent sequence alignment and phylogenetic analyses revealed the highest similarity (57.14%) with BvC3H from Beta vulgaris, exhibiting the closest evolutionary relationship with Beta vulgaris and Spinacia oleracea C3H protein. Quantitative real-time polymerase chain reaction demonstrated that SpC3H expression was markedly upregulated in both roots and leaves of S. portulacastrum under 800 mM NaCl treatment. Root expression peaked at 48 h (25.3-fold), whereas leaves displayed dual expression maxima at 12 h (7.9-fold) and 72 h (10.7-fold). Subcellular localization assays confirmed cytoplasmic distribution. Heterologous expression in Arabidopsis thaliana indicated that transgenic lines exhibited enhanced growth performance, higher fresh weight, and elevated lignin contents relative to wild-type plants under salt stress, accompanied by reduced reactive oxygen species (ROS) accumulation and lower relative electrical conductivity. Furthermore, activities of superoxide dismutase and peroxidase, together with expression of lignin biosynthesis-associated and antioxidant enzyme genes, were markedly elevated. Collectively, these findings establish that SpC3H confers salt tolerance by promoting lignin biosynthesis and activating antioxidant defenses to eliminate ROS, thereby providing a theoretical foundation for genetic improvement of plant salt tolerance.