Resistant Cotton Research Articles

Cotton 4-coumarate-CoA ligase 3 enhanced plant resistance to Verticillium dahliae by promoting jasmonic acid signaling-mediated vascular lignification and metabolic flux.

Lignins and their antimicrobial-related polymers cooperatively enhance plant resistance to pathogens. Several isoforms of 4-coumarate-coenzyme A ligases (4CLs) have been identified as indispensable enzymes involved in lignin and flavonoid biosynthetic pathways. However, their roles in plant-pathogen interaction are still poorly understood. This study uncovers the role of Gh4CL3 in cotton resistance to the vascular pathogen Verticillium dahliae. The cotton 4CL3-CRISPR/Cas9 mutant (CR4cl) exhibited high susceptibility to V. dahliae. This susceptibility was most probably due to the reduction in the total lignin content and the biosynthesis of several phenolic metabolites, e.g., rutin, catechin, scopoletin glucoside, and chlorogenic acid, along with jasmonic acid (JA) attenuation. These changes were coupled with a significant reduction in 4CL activity toward p-coumaric acid substrate, and it is likely that recombinant Gh4CL3 could specifically catalyze p-coumaric acid to form p-coumaroyl-coenzyme A. Thus, overexpression of Gh4CL3 (OE4CL) showed increasing 4CL activity that augmented phenolic precursors, cinnamic, p-coumaric, and sinapic acids, channeling into lignin and flavonoid biosyntheses and enhanced resistance to V. dahliae. Besides, Gh4CL3 overexpression activated JA signaling that instantly stimulated lignin deposition and metabolic flux in response to pathogen, which all established an efficient plant defense response system, and inhibited V. dahliae mycelium growth. Our results propose that Gh4CL3 acts as a positive regulator for cotton resistance against V. dahliae by promoting JA signaling-mediated enhanced cell wall rigidity and metabolic flux.

Interactions between Verticillium dahliae and cotton: pathogenic mechanism and cotton resistance mechanism to Verticillium wilt.

Cotton is widely grown in many countries around the world due to the huge economic value of the total natural fiber. Verticillium wilt, caused by the soil-borne pathogen Verticillium dahliae, is the most devastating disease that led to extensive yield losses and fiber quality reduction in cotton crops. Developing resistant cotton varieties through genetic engineering is an effective, economical, and durable strategy to control Verticillium wilt. However, there are few resistance gene resources in the currently planted cotton varieties, which has brought great challenges and difficulties for breeding through genetic engineering. Further revealing the molecular mechanism between V. dahliae and cotton interaction is crucial to discovering genes related to disease resistance. In this review, we elaborated on the pathogenic mechanism of V. dahliae and the resistance mechanism of cotton to Verticillium wilt. V. dahliae has evolved complex mechanisms to achieve pathogenicity in cotton, mainly including five aspects: (1) germination and growth of microsclerotia; (2) infection and successful colonization; (3) adaptation to the nutrient-deficient environment and competition of nutrients; (4) suppression and manipulation of cotton immune responses; (5) rapid reproduction and secretion of toxins. Cotton has evolved multiple physiological and biochemical responses to cope with V. dahliae infection, including modification of tissue structures, accumulation of antifungal substances, homeostasis of reactive oxygen species (ROS), induction of Ca2+ signaling, the mitogen-activated protein kinase (MAPK) cascades, hormone signaling, and PAMPs/effectors-triggered immune response (PTI/ETI). This review will provide an important reference for the breeding of new cotton germplasm resistant to Verticillium wilt through genetic engineering.

Geostatistical techniques to account for the heterogeneity of Fusarium wilt inoculum distribution in upland cotton field screening studies

AbstractVariable and uncontrollable environmental factors have a wide range of influence on crop field screening programs, with the potential to cause significant experimental errors in phenotypic data collection. These factors can be additive and negatively confound genetic studies. When field screening upland cotton for genetic resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4), the distribution and concentration of fungal inoculum in the field directly impact the disease severity, affecting the results of these studies. Variability among FOV4 screening fields and protocols has influenced the search for durable genetic resistance. To account for this spatial variability, rigorous use of check plots with predictable responses to FOV4 were planted throughout a screening nursery in Clint, TX, and scored for percent survival within each plot. The scores and locations were used to generate a predicted surface via kriging interpolation and conditional simulation, which estimate FOV4 inoculum pressure at every plot location in the field. These predictions created FOV4 pressure‐adjusted disease severity ratings in F3 generations of bi‐parental crosses between FOV4‐resistant and susceptible upland cotton lines. Environment‐adjusted phenotypes allow breeders to consider the environmental variance associated with the heterogenous distribution of the pathogen in the field. The techniques presented here are transferrable to any field screening program that needs to account for spatial variation of environmental factors.

Identification of candidate genes for aphid resistance in upland cotton by QTL mapping and expression analysis

Lignin is one of the main components of cell walls and is essential for resistance to insect pests in plants. Cotton plants are damaged by aphid (Aphis gossypii) worldwide but resistant breeding is undeveloped due to scarce knowledge on resistance genes and the mechanism. This study reported a lignin biosynthesis-related gene identified in the F2 population derived from the cross between cotton cultivars Xinluzao 61 (resistant to aphid) and Xinluzao 50 (susceptible to aphid). A quantitative trait locus was mapped on chromosome D04 with a logarithm of odds (LOD) score of 5.99 and phenotypic effect of 27%. RNA-seq analysis of candidate intervals showed that the expression level of GH_D04G1418 was higher in the resistant cultivar than in the susceptible cultivar. This locus is close to AtLAC4 in the phylogenetic tree and contains a conserved laccase domain. Hence, it was designated GhLAC4-3. Silencing of GhLAC4-3 in Xinluzao 61 via virus-induced gene silencing (VIGS) resulted in decreased lignin content and increased susceptibility to aphids. These results suggest that GhLAC4-3 might enhance aphid resistance by regulating lignin biosynthesis in cotton.

Acetylation of GhCaM7 enhances cotton resistance to Verticillium dahliae.

Protein lysine acetylation is an important post-translational modification mechanism involved in cellular regulation in eukaryotes. Calmodulin (CaM) is a ubiquitous Ca2+ sensor in eukaryotes and is crucial for plant immunity, but it is so far unclear whether acetylation is involved in CaM-mediated plant immunity. Here, we found that GhCaM7 is acetylated upon Verticillium dahliae (V. dahliae) infection and a positive regulator of V. dahliae resistance. Overexpressing GhCaM7 in cotton and Arabidopsis enhances V. dahliae resistance and knocking-down GhCaM7 makes cotton more susceptible to V. dahliae. Transgenic Arabidopsis plants overexpressing GhCaM7 with mutation at the acetylation site are more susceptible to V. dahliae than transgenics overexpressing the wild-type GhCaM7, implying the importance of the acetylated GhCaM7 in response to V. dahliae infection. Yeast two-hybrid, bimolecular fluorescent complementation, luciferase complementation imaging, and coimmunoprecipitation assays demonstrated interaction between GhCaM7 and an osmotin protein GhOSM34 that was shown to have a positive role in V. dahliae resistance. GhCaM7 and GhOSM34 are co-localized in the cell membrane. Upon V. dahliae infection, the Ca2+ content reduces almost instantly in plants with downregulated GhCaM7 or GhOSM34. Down regulating GhOSM34 enhances accumulation of Na+ and increases cell osmotic pressure. Comparative transcriptomic analyses between cotton plants with an increased or reduced expression level of GhCaM7 and wild-type plants indicate the involvement of jasmonic acid signaling pathways and reactive oxygen species in GhCaM7-enabled disease resistance. Together, these results demonstrate the involvement of CaM protein in the interaction between cotton and V. dahliae, and more importantly, the involvement of the acetylated CaM in the interaction.

Comprehensive genomic identification of cotton starch synthase genes reveals that GhSS9 regulates drought tolerance.

Starch metabolism is involved in the stress response. Starch synthase (SS) is the key enzyme in plant starch synthesis, which plays an indispensable role in the conversion of pyrophosphoric acid to starch. However, the SS gene family in cotton has not been comprehensively identified and systematically analyzed. In our study, a total of 76 SS genes were identified from four cotton genomes and divided into five subfamilies through phylogenetic analysis. Genetic structure analysis proved that SS genes from the same subfamily had similar genetic structure and conserved sequences. A cis-element analysis of the SS gene promoter showed that it mainly contains light response elements, plant hormone response elements, and abiotic stress elements, which indicated that the SS gene played key roles not only in starch synthesis but also in abiotic stress response. Furthermore, we also conducted a gene interaction network for SS proteins. Silencing GhSS9 expression decreased the resistance of cotton to drought stress. These findings suggested that SS genes could be related to drought stress in cotton, which provided theoretical support for further research on the regulation mechanism of SS genes on abiotic starch synthesis and sugar levels.

Bt cotton and modern insecticide adoption decreases Helicoverpa spp. population recruitment in a subtropical cropping system

AbstractExtensive crop sampling for Helicoverpa spp. pupae was undertaken (2017–2021) to provide insights as to how pest population dynamics have altered in a subtropical cropping system following the introduction of transgenic Bt cotton and newer generation insecticides for pulse production. Previously (1996–1999), a pattern of year‐round population cycling and build‐up was identified to occur between summer cotton (non‐Bt) and winter chickpea, enabled by widespread resistance to broad‐spectrum insecticides used at the time. Current pupae sampling was unable to recover pupae from Bt cotton, suggesting this crop had become a population sink rather than a source for Helicoverpa spp. Pupae were less abundant in pulses, with monthly counts varying from 0 to 3192/ha in chickpea being a fraction of previous densities that ranged from 10,000 to 100,000/ha whilst pupae were not detected in mungbean crops. Poor survival (0%–39.5%) of pupae collected from chickpea, likely due to sub‐lethal insecticide exposure during the larval stage, further limited population recruitment. The highest densities of pupae (up to 18,666/ha) were routinely recovered from unsprayed pigeon pea grown as refuges for Bt cotton resistance management, although Tachinid spp. parasitoids caused increasing pupal mortality with refuge age. This study suggests that the high control efficacy afforded by transgenic Bt traits incorporated into cotton and newer insecticides used on pulse crops has provided a form of area‐wide management that may explain suppression of Helicoverpa spp. pupae densities compared to levels previously recorded across the cropping system.

Nondestructive Evaluation of Cotton Genotypes for Resistance to Reniform Nematode

Identification of new sources of reniform nematode (Rotylenchulus reniformis Linford and Oliveira) resistance in cotton is critical to expanding host plant resistance to manage this important pathogen. Phenotyping plants in early breeding generations without destructive sampling would be useful for introgression of nematode resistance from exotic germplasm resources; therefore, a rapid, nondestructive method was developed to assess host plant resistance to the reniform nematode based on the number of females infecting the roots. In one set of experiments, the root system was cut off at 0, 1, 2.5, or 5 cm below the soil line and used to assess the number of females infecting this portion of the root system. Resistance could be accurately determined while leaving up to 5 cm of roots with the shoot. In a second set of experiments, the rate of plant recovery and reproductive development was evaluated using a combination of root retention (0, 1, 2.5 cm, or all root) and shoot retention (leaves at top two nodes, leaves at bottom two nodes, no leaves, all leaves) treatments. Plants more rapidly recovered using a treatment combination in which the top leaves and 2.5 cm roots were kept. This combination performed similarly to plants with neither shoots nor roots modified and was harvested 20 days sooner compared to some other treatment combinations.

Transcriptome Reveals the Molecular Mechanism of the ScALDH21 Gene from the Desert Moss Syntrichia caninervis Conferring Resistance to Salt Stress in Cotton.

The desert moss Syntrichia caninervis has proven to be an excellent plant material for mining resistance genes. The aldehyde dehydrogenase 21 (ScALDH21) gene from S. caninervis has been shown to confer tolerance to salt and drought, but it is unclear how the transgene ScALDH21 regulates tolerance to abiotic stresses in cotton. In the present work, we studied the physiological and transcriptome analyses of non-transgenic (NT) and transgenic ScALDH21 cotton (L96) at 0 day, 2 days, and 5 days after salt stress. Through intergroup comparisons and a weighted correlation network analysis (WGCNA), we found that there were significant differences between NT and L96 cotton in the plant hormone, Ca2+, and mitogen-activated protein kinase (MAPK) signaling pathways as well as for photosynthesis and carbohydrate metabolism. Overexpression of ScALDH21 significantly increased the expression of stress-related genes in L96 compared to NT cotton under both normal growth and salt stress conditions. These data suggest that the ScALDH21 transgene can scavenge more reactive oxygen species (ROS) in vivo relative to NT cotton and improve cotton resistance to salt stress by increasing the expression of stress-responsive genes, responding quickly to stress stimuli, enhancing photosynthesis and improving carbohydrate metabolism. Therefore, ScALDH21 is a promising candidate gene to improve resistance to salt stress, and the application of this gene in cotton provides new insights into molecular plant breeding.

Transcriptome and metabolome profiling reveals key pathways and metabolites involved in defense against Verticillium dahliae in upland cotton

Cotton is the main source of natural fiber in the textile industry, making it one of the most economically important fiber crops in the world. Verticillium wilt, caused by the pathogenic fungus Verticillium dahliae, is one of the most damaging biotic factors limiting cotton production. Mechanistic details of cotton defense responses to Verticillium wilt remain unclear. In this study, GFP-labeled strain of V. dahliae was used to track colonization in cotton roots, and clear conidial germination could be observed at 48 h post-inoculation (hpi), marking this as a crucial time point during infection. Transcriptome analysis identified 1523 and 8270 differentially expressed genes (DEGs) at 24 hpi and 48 hpi, respectively. Metabolomic screening found 78 differentially accumulated metabolites (DAMs) at 48 hpi. Conjoint analysis indicated that the phenylpropanoid biosynthesis pathway was activated in cotton infected with V. dahliae. Five metabolites in the phenylpropanoid biosynthesis pathway, including caffeic acid, coniferyl alcohol, coniferin, scopoletin and scopolin, could significantly inhibit the growth of V. dahliae in vitro, implicating their roles in cotton resistance to Verticillium wilt. The findings expand our understanding of molecular mechanisms underlying the defense response against V. dahliae infection in upland cotton, which may lead to further insights into controlling Verticillium wilt disease.

Eco-Friendly, Low-Cost, and Flexible Cotton Fabric for Capacitive Touchscreen Devices Based on Graphite

Cotton fabrics with high electrical conductivity were prepared using graphite dispersed in ethanol as the conductive material. The graphite particles were drop-cast onto the cotton fabrics at room temperature. The samples were characterized by SEM, EDX, XPS, and XRD. In addition, the electrical properties of the cotton samples were investigated using a four-probe technique. The concentration of the dispersed graphite was increased to a saturation concentration of 74.48 wt% to investigate the relation between the sheet resistance of the conductive cotton and the graphite concentration. With increasing graphite concentration, the sheet resistance decreased and reached the minimum value of 7.97 Ω/□ at a saturation concentration of 74.48 wt%. Samples with low, medium, and high graphite concentration showed semiconducting metallic behavior at a transition temperature of 90 °C. Based on their individual electrical properties, a smart glove was fabricated for touchscreen devices such as cell phones and self-service devices by dropping a small amount of dispersed graphite into one of the fingertips of the glove. The smart glove showed high efficiency and durability up to 10 wash cycles.

Mapping of quantitative trait loci controlling cotton leaf curl disease resistance in upland cotton

AbstractCotton leaf curl disease (CLCuD) is a major threat to cotton production in Asia and Africa. Using marker‐assisted breeding can be the best sustainable approach to tackle CLCuD. Identification of new QTLs in the indigenous cotton germplasm is necessary to combat CLCuD. The current study was designed to construct a genetic linkage map of bi‐parental F2:F3 populations developed from highly tolerant MNH‐886 and highly susceptible S‐12 cotton cultivars. One hundred seven CLCuD‐associated simple sequence repeat (SSR) marker alleles were identified as polymorphic and three new QTLs were found on chromosomes C11, C19 and C21. Two QTLs on chromosomes C11 and C19 were detected in both F2 and F3 populations in the region flanked by SSR markers CIR316 and BNL4094, and BNL285 and BNL3348, respectively. Whereas, one QTL on chromosome C21 was detected in the region flanked by SSR markers JESPR158 and JESPR135 in both F2 and F3 generations. The CLCuD‐associated QTLs identified in this study can help fine‐tune the molecular mapping of the QTLs on the cotton genome against CLCuD.

The Na+/H+ antiporter GbSOS1 interacts with SIP5 and regulates salt tolerance in Gossypium barbadense

Cotton is a globally cultivated economic crop and is a major source of natural fiber and edible oil. However, cotton production is severely affected by salt stress. Although Salt Overly Sensitive 1 (SOS1) is a well-studied Na+/H+ antiporter in multiple plant species, little is known about its function and regulatory mechanism in cotton. Here, we cloned a salt-induced SOS1 from sea-island cotton. Real-time quantitative PCR analysis revealed that GbSOS1 was induced by multiple stresses and phytohormones. Silencing GbSOS1 through virus-induced gene silencing significantly reduced cotton resistance to high Na+ but mildly affected Li+ tolerance. On the other hand, overexpression of GbSOS1 enhanced salt tolerance in yeast, Arabidopsis, and cotton largely due to the ability to maintain Na+ homeostasis in protoplasts. Yeast-two-hybrid assays and bimolecular fluorescence complementation identified a novel protein interacting with GbSOS1 on the plasma membrane, which we named SOS Interaction Protein 5 (SIP5). We found that the SIP5 gene encoded an unknown protein localized on the cell membrane. Silencing SIP5 significantly increased cotton tolerance to salt, exhibited by less wilting and plant death under salt stress. Our results revealed that GbSOS1 is crucial for cotton survival in saline soil, and SIP5 is a potentially negative regulator of SOS1-mediated salt tolerance in cotton. Overall, this study provides a theoretical basis for elucidating the molecular mechanism of SOS1, and a candidate gene for breeding salt-tolerant crops.

Evaluation of Meloidogyne Incognita and Rotylenchulus Reniformis Nematode-resistant Cotton Cultivars with Supplemental Corteva Agriscience Nematicides.

Meloidogyne incognita- and Rotylenchulus reniformis-resistant new cotton cultivars have recently become available, giving growers a new option in nematode management. The objectives of this study were: (i) to determine the yield potential of the new cultivars PHY 360 W3FE (M. incognita-resistant) and PHY 332 W3FE (R. reniformis-resistant) in nematode-infested fields and (ii) to evaluate the effects of combining the nematicides Reklemel (fluazaindolizine), Vydate C-LV (oxamyl), and the seed treatment BIOST Nematicide 100 (heat killed Burkholderia rinojenses and its non-living spent fermentation media) with resistant cotton cultivars on nematode population levels and lint yield. Field experiments in 2020 and 2021 indicated M. incognita population levels were 73% lower on PHY 360 W3FE (R) and 80% lower for R. reniformis on the PHY 332 W3FE (R) at 40 days after planting. Nematode eggs per gram of root were further reduced an average of 86% after the addition of Reklemel and Vydate C-LV when averaging both cultivars over the two years. Tests with BIOST Nematicide 100 + Reklemel + Vydate C-LV (0.56 + 2.5 L/ha) in both M. incognita and R. reniformis fields produced higher lint yields. Overall, planting PHY 360 W3FE (R) and PHY 332 W3FE (R) improved yields an average of 364 kg/ha while limiting nematode population increases. The addition of the nematicides further increased yields 152 kg/ha of the nematode-resistant cultivars.

NMR-Based Metabolomics: A New Paradigm to Unravel Defense-Related Metabolites in Insect-Resistant Cotton Variety through Different Multivariate Data Analysis Approaches.

Cotton (Gossypium hirsutum) is an economically important crop and is widely cultivated around the globe. However, the major problem of cotton is its high vulnerability to biotic and abiotic stresses. It has been around three decades since the cotton plant was genetically engineered with genes encoding insecticidal proteins (mainly Cry proteins) with an aim to protect it against insect attack. Several studies have been reported on the impact of these genes on cotton production and fiber quality. However, the metabolites responsible for conferring resistance in genetically modified cotton need to be explored. The current work aims to unveil the key metabolites responsible for insect resistance in Bt cotton and also compare the conventional multivariate analysis methods with deep learning approaches to perform clustering analysis. We aim to unveil the marker compounds which are responsible for inducing insect resistance in cotton plants. For this purpose, we employed 1H-NMR spectroscopy to perform metabolite profiling of Bt and non-Bt cotton varieties, and a total of 42 different metabolites were identified in cotton plants. In cluster analysis, deep learning approaches (linear discriminant analysis (LDA) and neural networks) showed better separation among cotton varieties compared to conventional methods (principal component analysis (PCA) and orthogonal partial least square discriminant analysis (OPLSDA)). The key metabolites responsible for inter-class separation were terpinolene, α-ketoglutaric acid, aspartic acid, stigmasterol, fructose, maltose, arabinose, xylulose, cinnamic acid, malic acid, valine, nonanoic acid, citrulline, and shikimic acid. The metabolites which regulated differently with the level of significance p < 0.001 amongst different cotton varieties belonged to the tricarboxylic acid cycle (TCA), Shikimic acid, and phenylpropanoid pathways. Our analyses underscore a biosignature of metabolites that might involve in inducing insect resistance in Bt cotton. Moreover, novel evidence from our study could be used in the metabolic engineering of these biological pathways to improve the resilience of Bt cotton against insect/pest attacks. Lastly, our findings are also in complete support of employing deep machine learning algorithms as a useful tool in metabolomics studies.

Genome-Wide Identification and Characterization of the PPO Gene Family in Cotton (Gossypium) and Their Expression Variations Responding to Verticillium Wilt Infection.

Polyphenol oxidases (PPOs) are copper-binding metalloproteinases encoded by nuclear genes, ubiquitously existing in the plastids of microorganisms, plants, and animals. As one of the important defense enzymes, PPOs have been reported to participate in the resistant processes that respond to diseases and insect pests in multiple plant species. However, PPO gene identification and characterization in cotton and their expression patterns under Verticillium wilt (VW) treatment have not been clearly studied. In this study, 7, 8, 14, and 16 PPO genes were separately identified from Gossypium arboreum, G. raimondii, G. hirsutum, and G. barbadense, respectively, which were distributed within 23 chromosomes, though mainly gathered in chromosome 6. The phylogenetic tree manifested that all the PPOs from four cotton species and 14 other plants were divided into seven groups, and the analyses of the conserved motifs and nucleotide sequences showed highly similar characteristics of the gene structure and domains in the cotton PPO genes. The dramatically expressed differences were observed among the different organs at various stages of growth and development or under the diverse stresses referred to in the published RNA-seq data. Quantitative real-time PCR (qRT-PCR) experiments were also performed on the GhPPO genes in the roots, stems, and leaves of VW-resistant MBI8255 and VW-susceptible CCRI36 infected with Verticillium dahliae V991, proving the strong correlation between PPO activity and VW resistance. A comprehensive analysis conducted on cotton PPO genes contributes to the screening of the candidate genes for subsequent biological function studies, which is also of great significance for the in-depth understanding of the molecular genetic basis of cotton resistance to VW.

Strigolactones positively regulate Verticillium wilt resistance in cotton via crosstalk with other hormones.

Verticillium wilt caused by Verticillium dahliae is a serious vascular disease in cotton (Gossypium spp.). V. dahliae induces the expression of the CAROTENOID CLEAVAGE DIOXYGENASE 7 (GauCCD7) gene involved in strigolactone (SL) biosynthesis in Gossypium australe, suggesting a role for SLs in Verticillium wilt resistance. We found that the SL analog rac-GR24 enhanced while the SL biosynthesis inhibitor TIS108 decreased cotton resistance to Verticillium wilt. Knock-down of GbCCD7 and GbCCD8b genes in island cotton (Gossypium barbadense) decreased resistance, whereas overexpression of GbCCD8b in upland cotton (Gossypium hirsutum) increased resistance to Verticillium wilt. Additionally, Arabidopsis (Arabidopsis thaliana) SL mutants defective in CCD7 and CCD8 putative orthologs were susceptible, whereas both Arabidopsis GbCCD7- and GbCCD8b-overexpressing plants were more resistant to Verticillium wilt than wild-type (WT) plants. Transcriptome analyses showed that several genes related to the jasmonic acid (JA)- and abscisic acid (ABA)-signaling pathways, such as MYELOCYTOMATOSIS 2 (GbMYC2) and ABA-INSENSITIVE 5, respectively, were upregulated in the roots of WT cotton plants in responses to rac-GR24 and V. dahliae infection but downregulated in the roots of both GbCCD7- and GbCCD8b-silenced cotton plants. Furthermore, GbMYC2 suppressed the expression of GbCCD7 and GbCCD8b by binding to their promoters, which might regulate the homeostasis of SLs in cotton through a negative feedback loop. We also found that GbCCD7- and GbCCD8b-silenced cotton plants were impaired in V. dahliae-induced reactive oxygen species (ROS) accumulation. Taken together, our results suggest that SLs positively regulate cotton resistance to Verticillium wilt through crosstalk with the JA- and ABA-signaling pathways and by inducing ROS accumulation.

GhMYB102 promotes drought resistance by regulating drought-responsive genes and ABA biosynthesis in cotton (Gossypium hirsutum L.)

The MYB transcription factor (TF) family is among the largest TF families and plays an important role in plant growth and stress response. However, few studies have investigated the role of the MYB gene in drought resistance in cotton. In this study, we analysed the drought transcriptomic data of cotton and identified that the GhMYB102 gene was significantly upregulated in upland cotton during the early stages of drought stress. Bioinformatics analysis showed that the amino acid sequence encoded by GhMYB102 contained two highly conserved MYB binding domains belonging to R2R3-MYB TFs. GhMYB102 was most closely related to AtMYB102. GhMYB102 is mainly expressed in roots and is induced by abiotic stresses and abscisic acid (ABA); it is localised in the nucleus and has transcriptional activation activity. Silencing of GhMYB102 decreased plant drought resistance. In addition, dual-luciferase assays and yeast single hybridisation analysis showed that GhMYB102 could directly bind the MYB motif elements in the promoter regions of GhNCED1 and GhZAT10. These results indicate that GhMYB102 plays a positive role in drought tolerance by regulating the expression of GhNCED1 and GhZAT10. Thus, GhMYB102 enhances drought resistance by participating in ABA biosynthesis or regulating the expression of drought-responsive genes.

Genome-wide analysis of Hsp40 and Hsp70 gene family in four cotton species provides insights into their involvement in response to Verticillium dahliae and abiotic stress.

Introduction: Cotton is an important economic crop to provide natural fibers as raw materials to textile industry, and is significantly affected by biotic and abiotic stress during the whole growth stage, in which Verticillium wilt (VW) caused by Verticillium dahliae is one of the most destructive disease to lead to a significant yield reduction. Heat shock proteins (Hsps) are important molecular chaperones, and play crucial roles in plant growth, development, resistance to biotic and abiotic stress. Hsp40 and Hsp70 are two key Hsps in cell chaperone network, however, the function and regulatory mechanism of Hsp40 and Hsp70 members in VW resistance and abiotic stress in cotton are largely unknown. Methods and Results: Herein, a systematic and comprehensive analysis of Hsp40s and Hsp70s in four cotton species of Gossypium arboretum, G. raimondii, G. hirsutum, and G. barbadense were performed. A total of 291 Hsp40s and 171 Hsp70s identified in four Gossypium species. Sequence analysis revealed that all Hsp40 proteins contained J domain that provides the binding sites to Hsp70. Protein-protein interaction prediction analysis displayed that GhHsp40-55 might interact with GhHsp70-2 and GhHsp70-13, suggesting their potential function as protein complex. Promoter cis-acting element analysis demonstrated that multiple cis-elements related to disease and stress response consists in GhHsp40 and GhHsp70 promoters. Further expression analysis showed that eight GhHsp40s (Hsp40-2,4,8,11,20,23,53,55) and seven GhHsp70s (Hsp70-2,3,6,8,13,19,22) were up-regulated after V. dahliae infection. In addition, five GhHsp40s (Hsp40-2,8,11,53,55) and four GhHsp70s (Hsp70-3,6,8,13) were up-regulated after salt treatment, six GhHsp40s (Hsp40-4,11,20,23) and three GhHsp70s (Hsp70-2,8,19) were up-regulated after drought treatment, four GhHsp40s (Hsp40-2,11,20,23) and four GhHsp70s (Hsp70-3,6,19,22) were up-regulated after temperature treatment, suggesting these Hsps have possible important function in the process of abiotic stress response. Discussion: Our results lay a foundation for understanding the function of Hsp40 and Hsp70 in the resistance against V. dahliae and abiotic stress, and elucidating the regulatory mechanism of the protein complex, evolution and molecular mechanism under stress.

Identification of sugar transporter genes and their roles in the pathogenicity of Verticillium dahliae on cotton.

Verticillium wilt (VW) caused by Verticillium dahliae is a soil-borne vascular fungal disease that severely affects cotton yield and fiber quality. Sugar metabolism plays an important role in the growth and pathogenicity of V. dahliae. However, limited information is known about the sugar transporter genes and their roles in the growth and pathogenicity of V. dahliae. In this study, genome-wide identification of sugar transporter genes in V. dahliae was conducted and the expression profiles of these genes in response to root exudates from cotton varieties susceptible or resistant to V. dahliae were investigated based on RNA-seq data. Tobacco Rattle Virus-based host-induced gene silencing (TRV-based HIGS) and artificial small interfering RNAs (asiRNAs) were applied to investigate the function of candidate genes involved in the growth and pathogenic process of V. dahliae. A total of 65 putative sugar transporter genes were identified and clustered into 8 Clades. Of the 65 sugar transporter genes, 9 were found to be induced only by root exudates from the susceptible variety, including VdST3 and VdST12 that were selected for further functional study. Silencing of VdST3 or VdST12 in host plants by TRV-based HIGS reduced fungal biomass and enhanced cotton resistance against V. dahliae. Additionally, silencing of VdST12 and VdST3 by feeding asiRNAs targeting VdST12 (asiR815 or asiR1436) and VdST3 (asiR201 or asiR1238) inhibited fungal growth, exhibiting significant reduction in hyphae and colony diameter, with a more significant effect observed for the asiRNAs targeting VdST12. The inhibitory effect of asiRNAs on the growth of V. dahliae was enhanced with the increasing concentration of asiRNAs. Silencing of VdST12 by feeding asiR815+asiR1436 significantly decreased the pathogenicity of V. dahliae. The results suggest that VdST3 and VdST12 are sugar transporter genes required for growth and pathogenicity of V. dahliae and that asiRNA is a valuable tool for functional characterization of V. dahliae genes.