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Background The study of quantitative trait loci (QTL) in cotton (Gossypium spp.) is focused on traits of agricultural significance. Previous studies have identified a plethora of QTL attributed to fiber quality, disease and pest resistance, branch number, seed quality and yield and yield related traits, drought tolerance, and morphological traits. However, results among these studies differed due to the use of different genetic populations, markers and marker densities, and testing environments. Since two previous meta-QTL analyses were performed on fiber traits, a number of papers on QTL mapping of fiber quality, yield traits, morphological traits, and disease resistance have been published. To obtain a better insight into the genome-wide distribution of QTL and to identify consistent QTL for marker assisted breeding in cotton, an updated comparative QTL analysis is needed. Results In this study, a total of 1,223 QTL from 42 different QTL studies in Gossypium were surveyed and mapped using Biomercator V3 based on the Gossypium consensus map from the Cotton Marker Database. A meta-analysis was first performed using manual inference and confirmed by Biomercator V3 to identify possible QTL clusters and hotspots. QTL clusters are composed of QTL of various traits which are concentrated in a specific region on a chromosome, whereas hotspots are composed of only one trait type. QTL were not evenly distributed along the cotton genome and were concentrated in specific regions on each chromosome. QTL hotspots for fiber quality traits were found in the same regions as the clusters, indicating that clusters may also form hotspots. Conclusions Putative QTL clusters were identified via meta-analysis and will be useful for breeding programs and future studies involving Gossypium QTL. The presence of QTL clusters and hotspots indicates consensus regions across cultivated tetraploid Gossypium species, environments, and populations which contain large numbers of QTL, and in some cases multiple QTL associated with the same trait termed a hotspot. This study combines two previous meta-analysis studies and adds all other currently available QTL studies, making it the most comprehensive meta-analysis study in cotton to date. [ABSTRACT FROM AUTHOR]

Background Cotton is the dominant textile crop and also serves as an important oil crop. An estimated 15% economic loss associated with cotton production in China has been caused by diseases, and no resistance genes have been cloned in this crop. Molecular markers developed from resistance gene homologues (RGHs) might be tightly linked with target genes and could be used for marker-assisted selection (MAS) or gene cloning. Results To genetically map expressed RGHs, 100 potential pathogenesis-related proteins (PRPs) and 215 resistance gene analogs (RGAs) were identified in the cotton expressed sequence tag database, and 347 specific primers were developed. Meanwhile, 61 cotton genome-derived RGA markers and 24 resistance gene analog polymorphism (RGAP) markers from published papers were included to view their genomic distribution. As a result, 38 EST-derived and 17 genome-derived RGH markers were added to our interspecific genetic map. These 55 markers were distributed on 18 of the 26 cotton chromosomes, with 34 markers on 6 chromosomes (Chr03, Chr04, Chr11, Chr17, Chr19 and Chr26). Homologous RGHs tended to be clustered; RGH clusters appeared on 9 chromosomes, with larger clusters on Chr03, Chr04 and Chr19, which suggests that RGH clusters are widely distributed in the cotton genome. Expression analysis showed that 19 RGHs were significantly altered after inoculation with the V991 stain of Verticillium dahliae. Comparative mapping showed that four RGH markers were linked with mapped loci for Verticillium wilt resistance. Conclusions The genetic mapping of RGHs confirmed their clustering in cotton genome. Expression analysis and comparative mapping suggest that EST-derived RGHs participate in cotton resistance. RGH markers are seemed to be useful tools to detected resistance loci and identify candidate resistance genes in cotton. [ABSTRACT FROM AUTHOR]

Background: Cotton (Gossypium spp.), as the world's most utilized textile fibre source, is an important, economically valuable crop worldwide. Understanding the genomic variation of tetraploid cotton species is important for exploitation of the excellent characteristics of wild cotton and for improving the diversity of cotton in breeding. However, the discovery of DNA polymorphisms in tetraploid cotton genomes has lagged behind other important crops. Results: A total of 111,795,823 reads, 467,735 specific length amplified fragment (SLAF) tags and 139,176 highquality DNA polymorphisms were identified using specific length amplified fragment sequencing (SLAF-seq), including 132,880 SNPs and 6,296 InDels between the reference genome (TM-1) and the five tetraploid cotton species. Intriguingly, gene ontology (GO) enrichment analysis revealed that a number of significant terms were related to reproduction in G. barbadense acc. 3-79. Based on the new data sets, we reconstructed phylogenetic trees that showed a high concordance to the phylogeny of diploid and polyploid cottons. A large amount of interspecific genetic variations were identified, and some of them were validated by the single-strand conformation polymorphism (SSCP) method, which will be applied in introgression genetics and breeding with G. hirsutum cv. Emian22 as the receptor and the other species as donors. Conclusions: Using SLAF-seq, a large number of DNA polymorphisms were identified. The comprehensive analysis of DNA polymorphisms provided invaluable insights into the different tetraploid cotton species. More importantly, the identification of numerous interspecific genetic variations provides the basis and is very practical for future introgression breeding. The results presented herein provide a valuable genomic resource for new insights into the genetics and breeding of cotton. [ABSTRACT FROM AUTHOR]

Background: Dissecting genome organization is indispensable for further functional and applied studies. As genome sequences data shown, cotton genomes contain more than 60% repetitive sequences, so study on repetitive sequences composition, structure, and distribution is the key step to dissect cotton genome. Results: In this study, a bacterial artificial chromosome (BAC) clone enriched in repetitive sequences, was discovered initiatively by fluorescence in situ hybridization (FISH). FISHing with allotetraploidy cotton as target DNA, dispersed signals on most regions of all A sub-genome chromosomes, and only middle regions of all D sub-genome chromosomes were detected. Further FISHing with other cotton species bearing A or D genome as target DNA, specific signals were viewed. After BAC sequencing and bioinformational analysis, 129 repeat elements, size about 57,172 bp were found, accounting for more than 62% of the BAC sequence (91,238 bp). Among them, a type of long terminal repeat-retrotransposon (LTR-RT), LTR/Gypsy was the key element causing the specific FISH results. Using the fragments of BAC matching with the identified Gypsy-like LTR as probes, the BAC-57I23-like FISH signals were reappeared. Running BLASTN, the fragments had good match with all chromosomes of G. arboreum (A2) genome and A sub-genome of G. hirsutum (AD1), and had relatively inferior match with all chromosomes of D sub-genome of AD1, but had little match with the chromosomes of G. raimondii (D5) genome, which was consistent with the FISH results. Conclusion: A repeats-enriched cytogenetic marker to identify A and D sub-genomes of Gossypium was discovered by FISH. Combined sequences analysis with FISH verification, the assembly quality of repetitive sequences in the allotetraploidy cotton draft genome was assessed, and better chromosome belonging was verified. We also found the genomic distribution of the identified Gypsy-LTR-RT was similar to the distribution of heterochromatin. The expansion of this type of Gypsy-LTR-RT in heterochromatic regions may be one of the major reasons for the size gap between A and D genome. The findings showed here will help to understand the composition, structure, and evolution of cotton genome, and contribute to the further perfection of the draft genomes of cotton. [ABSTRACT FROM AUTHOR]

Background Availability of molecular markers has proven to be an efficient tool in facilitating progress in plant breeding, which is particularly important in the case of less researched crops such as cotton. Considering the obvious advantages of single nucleotide polymorphisms (SNPs) and insertion-deletion polymorphisms (InDels), expressed sequence tags (ESTs) were analyzed in silico to identify SNPs and InDels in this study, aiming to develop more molecular markers in cotton. Results A total of 1,349 EST-based SNP and InDel markers were developed by comparing ESTs between Gossypium hirsutum and G. barbadense, mining G. hirsutum unigenes, and analyzing 3' untranslated region (3'UTR) sequences. The marker polymorphisms were investigated using the two parents of the mapping population based on the single-strand conformation polymorphism (SSCP) analysis. Of all the markers, 137 (10.16%) were polymorphic, and revealed 142 loci. Linkage analysis using a BC1 population mapped 133 loci on the 26 chromosomes. Statistical analysis of base variations in SNPs showed that base transitions accounted for 55.78% of the total base variations and gene ontology indicated that cotton genes varied greatly in harboring SNPs ranging from 1.00 to 24.00 SNPs per gene. Sanger sequencing of three randomly selected SNP markers revealed discrepancy between the in silico predicted sequences and the actual sequencing results. Conclusions In silico analysis is a double-edged blade to develop EST-SNP/InDel markers. On the one hand, the designed markers can be well used in tetraploid cotton genetic mapping. And it plays a certain role in revealing transition preference and SNP frequency of cotton genes. On the other hand, the developmental efficiency of markers and polymorphism of designed primers are comparatively low. [ABSTRACT FROM AUTHOR]

Background MicroRNAs (miRNAs) are small, endogenously expressed, non-coding RNA molecules involved in gene transcription and expression that combine with specific mRNA site of target genes to inhibit protein synthesis or degrade mRNA. Since the first plant miRNA was reported in 2002, numerous new miRNAs and their targets have been discovered via highthroughput sequencing and computational approaches. However, the genetic variation of miRNA genes is poorly understood due to the lack of miRNA-specific DNA markers. Results To study the genetic variation and map miRNAs and their putative target genes in cotton, we designed specific primers based on pre-miRNAs and published putative target genes. A total of 83 pre-miRNA primers and 1,255 putative target gene primers were surveyed, and 9 premiRNA polymorphic loci were mapped on 7 of the 26 tetraploid cotton chromosomes. Furthermore, 156 polymorphic loci of the target genes were mapped on the cotton genome. To map more miRNA loci, miRNA-based SRAP (sequence-related amplified polymorphism) markers were used to map an additional 54 polymorphic loci on the cotton genome with the exception of Chr01, Chr22, and Chr24. Finally, a network between miRNAs and their targets was constructed. All pre-miRNAs and 98 putative target genes were selected for RT-PCR analysis, revealing unique expression patterns across different fiber development stages between the mapping parents. Conclusions Our data provide an overview of miRNAs, their putative targets, and their network in cotton as well as comparative expression analyses between Gossypium hirsutum and G. barbadense. These data provide a foundation for understanding miRNA regulation during cotton fiber development. [ABSTRACT FROM AUTHOR]