Identification and function analysis of GABA branch three gene families in the cotton related to abiotic stresses.

γ -aminobutyric acid (GABA) is closely related to the growth, development and stress resistance of plants. Combined with the previous study of GABA to promote the cotton against abiotic stresses, the characteristics and expression patterns of GABA branch gene family laid the foundation for further explaining its role in cotton stress mechanism. Members of GAD, GAB-T and SSADH (three gene families of GABA branch) were identified from the Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum and Gossypium raimondii genome. The GABA branch genes were 10 GAD genes, 4 GABA-T genes and 2 SSADH genes. The promoter sequences of genes mainly contains response-related elements such as light, hormone and environment.Phylogenetic analysis shows that GAD indicating that even in the same species, the homologous sequences in the family. The GABA-T gene of each cotton genus was in sum the family had gene loss in the process of dicotyledon evolution. SSADH families Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum and Gossypium raimondii were closely related to the dicot plants.GABA gene is involved in the regulation of salt stress and high temperature in Gossypium hirsutum.GABA attenuated part of the abiotic stress damage by increasing leaf protective enzyme activity and reducing reactive oxygen species production.This lays the foundation for a thorough analysis of the mechanism of GABA in cotton stress resistance.

Genomic and epigenomic insights into the mechanism of cold response in upland cotton (Gossypium hirsutum).

Functional genome research, including gene transcriptional and posttranslational modifications of histones, can benefit greatly from a high-quality genome assembly. Histone modification plays a significant role in modulating the responses to abiotic stress in plants. However, there are limited reports on the involvement of dynamic changes in histone modification in cold stress response in upland cotton. In this study, the genome of an elite accession, YM11, with considerable cold stress tolerance was de novo assembled, which yielded a genome of 2343.06 Mb with a contig N50 of 88.96 Mb, and a total of 73,821 protein-coding gene models were annotated. Comparisons among YM11 and five Gossypium allopolyploid cotton assemblies highlighted a large amount of structural variations and presence/absence variations. We analyzed transcriptome and metabolome changes in YM11 seedlings subjected to cold stress. Using the CUT&Tag method, genome-wide H3K4me3 and H3K9ac modification patterns and effect of histone changes on gene expression were profiled during cold stress. Significant and consistently changing histone modifications and the gene expressions were screened, of which transcription factors (TFs) were highlighted. Our results suggest a positive correlation between the changes in H3K4me3, H3K9ac modifications and cold stress-responsive gene activation. This genome assembly and comprehensive analysis of genome-wide histone modifications and gene expression provide insights into the genomic variation and epigenetic responses to cold stress in upland cotton.

Genome-wide identification and expression reveal the involvement of the FCS-like zinc finger (FLZ) gene family in Gossypium hirsutum at low temperature.

FCS-like zinc finger (FLZ) is a plant-specific gene family that plays an important regulatory role in plant growth and development and its response to stress. However, studies on the characteristics and functions of cotton FLZ family genes are still lacking. This study systematically identified members of the cotton FLZ gene family based on cotton genome data. The cotton FLZ family genes were systematically analyzed by bioinformatics, and their expression patterns in different tissues and under low-temperature stress were analyzed by transcriptome and qRT-PCR. The G. hirsutum genome contains 56 FLZ genes distributed on 20 chromosomes, and most of them are located in the nucleus. According to the number and evolution analysis of FLZ family genes, FLZ family genes can be divided into five subgroups in cotton. The G. hirsutum FLZ gene has a wide range of tissue expression types, among which the expression is generally higher in roots, stems, leaves, receptacles and calyx. Through promoter analysis, it was found that it contained the most cis-acting elements related to methyl jasmonate (MeJA) and abscisic acid (ABA). Combined with the promoter and qRT-PCR results, it was speculated that GhFLZ11, GhFLZ25, GhFLZ44 and GhFLZ55 were involved in the response of cotton to low-temperature stress. Taken together, our findings suggest an important role for the FLZ gene family in the cotton response to cold stress. This study provides an important theoretical basis for further research on the function of the FLZ gene family and the molecular mechanism of the cotton response to low temperature.

Whole Transcriptome Sequencing Reveals Drought Resistance-Related Genes in Upland Cotton.

China, particularly the cotton-growing province of Xinjiang, is experiencing acute agricultural water shortages, stifling the expansion of the cotton sector. Discovering drought resistance genes in cotton and generating high-quality, drought-resistant cotton varieties through molecular breeding procedures are therefore critical to the cotton industry's success. The drought-resistant cotton variety Xinluzhong No. 82 and the drought-sensitive cotton variety Kexin No. 1 were utilised in this study to uncover a batch of drought-resistant candidate genes using whole transcriptome sequencing. The following are the key research findings: A competing endogenous RNA network (ceRNA) was built using complete transcriptional sequencing to screen the core genes in the core pathway, and two drought-related candidate genes were discovered. It was found that γ-aminobutyric acid aminotransferase (GhGABA-T, Gohir.A11G156000) was upregulated at 0 h vs. 12 h and downregulated at 12 h vs. 24 h. L-Aspartate oxidase (GhAO, Gohir.A07G220600) was downregulated at 0 h vs. 12 h and upregulated at 12 h vs. 24 h. GABA-T is analogous to a pyridoxal phosphate-dependent transferase superfamily protein (POP2) in Arabidopsis thaliana and influences plant drought resistance by controlling γ-aminobutyric acid (GABA) concentration. The analogue of GhAO in A. thaliana is involved in the early steps of nicotinamide adenine dinucleotide (NAD) production as well as in plant antioxidant responses. This study revealed that gene expression regulatory networks can be used for rapid screening of reliable drought resistance genes and then utilised to validate gene function.

Conservation and Divergence of Phosphoenolpyruvate Carboxylase Gene Family in Cotton.

Phosphoenolpyruvate carboxylase (PEPC) is an important enzyme in plants, which regulates carbon flow through the TCA cycle and controls protein and oil biosynthesis. Although it is important, there is little research on PEPC in cotton, the most important fiber crop in the world. In this study, a total of 125 PEPCs were identified in 15 Gossypium genomes. All PEPC genes in cotton are divided into six groups and each group generally contains one PEPC member in each diploid cotton and two in each tetraploid cotton. This suggests that PEPC genes already existed in cotton before their divergence. There are additional PEPC sub-groups in other plant species, suggesting the different evolution and natural selection during different plant evolution. PEPC genes were independently evolved in each cotton sub-genome. During cotton domestication and evolution, certain PEPC genes were lost and new ones were born to face the new environmental changes and human being needs. The comprehensive analysis of collinearity events and selection pressure shows that genome-wide duplication and fragment duplication are the main methods for the expansion of the PEPC family, and they continue to undergo purification selection during the evolutionary process. PEPC genes were widely expressed with temporal and spatial patterns. The expression patterns of PEPC genes were similar in G. hirsutum and G. barbadense with a slight difference. PEPC2A and 2D were highly expressed in cotton reproductive tissues, including ovule and fiber at all tested developmental stages in both cultivated cottons. However, PEPC1A and 1D were dominantly expressed in vegetative tissues. Abiotic stress also induced the aberrant expression of PEPC genes, in which PEPC1 was induced by both chilling and salinity stresses while PEPC5 was induced by chilling and drought stresses. Each pair (A and D) of PEPC genes showed the similar response to cotton development and different abiotic stress, suggesting the similar function of these PEPCs no matter their origination from A or D sub-genome. However, some divergence was also observed among their origination, such as PEPC5D was induced but PEPC5A was inhibited in G. barbadense during drought treatment, suggesting that a different organized PEPC gene may evolve different functions during cotton evolution. During cotton polyploidization, the homologues genes may refunction and play different roles in different situations.

Analysis of the genetic structure and diversity of upland cotton groups in different planting areas based on SNP markers.

Genetic diversity, kinship and population genetic structure analyses of Gossypium hirsutum germplasm can provide a better understanding of the origin and evolution of G. hirsutum biodiversity. In this study, adopt 273 elite upland cotton cultivar accessions collected from around the world, and especially from China to get 1,313,331 SNP molecular markers, it were used to construct a phylogenetic tree of each sample using MEGAX, to perform population structure analysis by ADMIXTURE software and principal component analysis (PCA) by EIGENSOFT software, and to estimate relatedness using SPAGeDi. ADMIXTURE software divided the experimental cotton population into 16 subgroups, and the Gossypium hirsutum samples could be roughly clustered according to source place, but there were some overlapping characteristics among samples. The experimental cotton population was divided into six groups according to source to calculate the genetic diversity index (H), and the obtained value (0.306) was close to that for germplasm collected by others in China. Cluster 4 had a relatively high genetic diversity level (0.390). The degrees of genetic differentiation within the experimental cotton population groups were low (the population differentiation indexes ranged from 0.02368 to 0.10664). The genetic distance among cotton accessions varied from 0.000332651 to 0.562664014, with an average of 0.25240429. The results of this study may provide a basis for mining elite alleles and using them for subsequent association analysis.

Nanopore-Based Comparative Transcriptome Analysis Reveals the Potential Mechanism of High-Temperature Tolerance in Cotton (Gossypium hirsutum L.).

Extreme high temperatures are threatening cotton production around the world due to the intensification of global warming. To cope with high-temperature stress, heat-tolerant cotton cultivars have been bred, but the heat-tolerant mechanism remains unclear. This study selected heat-tolerant ('Xinluzao36') and heat-sensitive ('Che61-72') cultivars of cotton treated with high-temperature stress as plant materials and performed comparative nanopore sequencing transcriptome analysis to reveal the potential heat-tolerant mechanism of cotton. Results showed that 120,605 nonredundant sequences were generated from the raw reads, and 78,601 genes were annotated. Differentially expressed gene (DEG) analysis showed that a total of 19,600 DEGs were screened; the DEGs involved in the ribosome, heat shock proteins, auxin and ethylene signaling transduction, and photosynthesis pathways may be attributed to the heat tolerance of the heat-tolerant cotton cultivar. This study also predicted a total of 5118 long non-coding RNAs (lncRNAs)and 24,462 corresponding target genes. Analysis of the target genes revealed that the expression of some ribosomal, heat shock, auxin and ethylene signaling transduction-related and photosynthetic proteins may be regulated by lncRNAs and further participate in the heat tolerance of cotton. This study deepens our understandings of the heat tolerance of cotton.

Genome-Wide Comparative Analysis of Heat Shock Transcription Factors Provides Novel Insights for Evolutionary History and Expression Characterization in Cotton Diploid and Tetraploid Genomes.

Heat shock transcription factors (HSFs) are involved in environmental stress response and plant development, such as heat stress and flowering development. According to the structural characteristics of the HSF gene family, HSF genes were classified into three major types (HSFA, HSFB, and HSFC) in plants. Using conserved domains of HSF genes, we identified 621 HSF genes among 13 cotton genomes, consisting of eight diploid and five tetraploid genomes. Phylogenetic analysis indicated that HSF genes among 13 cotton genomes were grouped into two different clusters: one cluster contained all HSF genes of HSFA and HSFC, and the other cluster contained all HSF genes of HSFB. Comparative analysis of HSF genes in Arabidopsis thaliana, Gossypium herbaceum (A1), Gossypium arboreum (A2), Gossypium raimondii (D5), and Gossypium hirsutum (AD1) genomes demonstrated that four HSF genes were inherited from a common ancestor, A0, of all existing cotton A genomes. Members of the HSF gene family in G. herbaceum (A1) genome indicated a significant loss compared with those in G. arboretum (A2) and G. hirsutum (AD1) A genomes. However, HSF genes in G. raimondii (D5) showed relative loss compared with those in G. hirsutum (AD1) D genome. Analysis of tandem duplication (TD) events of HSF genes revealed that protein-coding genes among different cotton genomes have experienced TD events, but only the two-gene tandem array was detected in Gossypium thurberi (D1) genome. The expression analysis of HSF genes in G. hirsutum (AD1) and Gossypium barbadense (AD2) genomes indicated that the expressed HSF genes were divided into two different groups, respectively, and the expressed HSF orthologous genes between the two genomes showed totally different expression patterns despite the implementation of the same abiotic stresses. This work will provide novel insights for the study of evolutionary history and expression characterization of HSF genes in different cotton genomes and a widespread application model for the study of HSF gene families in plants.

Genome-Wide Association Analysis of Salt-Tolerant Traits in Terrestrial Cotton at Seedling Stage.

Soil salinization is the main abiotic stress factor affecting agricultural production worldwide, and salt stress has a significant impact on plant growth and development. Cotton is one of the most salt-tolerant crops. Therefore, the selection and utilization of salt-tolerant germplasm resources and the excavation of salt resistance genes play important roles in improving cotton production in saline-alkali soils. In this study, we analysed the population structure and genetic diversity of a total 149 cotton plant materials including 137 elite Gossypium hirsutum cultivar accessions collected from China and 12 elite Gossypium hirsutum cultivar accessions collected from around the world. Illumina Cotton SNP 70 K was used to obtain genome-wide single-nucleotide polymorphism (SNP) data for 149 elite Gossypium hirsutum cultivar accessions, and 18,430 highly consistent SNP loci were obtained by filtering. It was assessed by using PCA principal component analysis so that the 149 elite Gossypium hirsutum cultivar accessions could be divided into two subgroups, including subgroup 1 with 78 materials and subgroup 2 with 71 materials. Using the obtained SNP and other marker genotype test results, under salt stress, the salt tolerance traits 3d Germination potential, 3d Radicle length drop rate, 7d Germination rate, 7d Radicle length drop rate, 7d Germination weight, 3d Radicle length, 7d Radicle length, Relative Germination potential, Relative Germination rate, 7d Radicle weight drop rate, Salt tolerance index 3d Germination potential index, 3d Radicle length index, 7d Radicle length index, 7d Radicle weight index and 7d Germination rate index were evaluated by GWAS (genome-wide association analysis). A total of 27 SNP markers closely related to the salt tolerance traits and 15 SNP markers closely related to the salt tolerance index were detected. At the SNP locus associated with phenotyping, Gh_D01G0943, Gh_D01G0945, Gh_A01G0906, Gh_A01G0908, Gh_D08G1308 and Gh_D08G1309 related to plant salt tolerance were detected, and they were found to be involved in intracellular transport, sucrose synthesis, osmotic pressure balance, transmembrane transport, N-glycosylation, auxin response and cell amplification. This study provides a theoretical basis for the selection and breeding of salt-tolerant upland cotton varieties.

Genetic diversity and structure of elite cotton germplasm (Gossypium hirsutum L.) using genome-wide SNP data.

Cotton (Gossypium spp.) is the most important natural textile fiber crop, and Gossypium hirsutum L. is responsible for 90% of the annual cotton crop in the world. Information on cotton genetic diversity and population structure is essential for new breeding lines. In this study, we analyzed population structure and genetic diversity of 288 elite Gossypium hirsutum cultivar accessions collected from around the world, and especially from China, using genome-wide single nucleotide polymorphisms (SNP) markers. The average polymorphsim information content (PIC) was 0.25, indicating a relatively low degree of genetic diversity. Population structure analysis revealed extensive admixture and identified three subgroups. Phylogenetic analysis supported the subgroups identified by STRUCTURE. The results from both population structure and phylogenetic analysis were, for the most part, in agreement with pedigree information. Analysis of molecular variance revealed a larger amount of variation was due to diversity within the groups. Establishment of genetic diversity and population structure from this study could be useful for genetic and genomic analysis and systematic utilization of the standing genetic variation in upland cotton.