Generation of ESTs for flowering gene discovery and SSR marker development in upland cotton

Genetic Analysis of Cotton Fiber Traits in Gossypium Hybrid Lines

Cotton plays a crucial role in the progress of the textile industry and the betterment of human life by providing natural fibers. In our study, we explored the genetic determinants of cotton architecture and fiber yield and quality by crossbreeding Gossypium hirsutum and Gossypium barbadense, creating a recombinant inbred line (RIL) population. Utilizing SNP markers, we constructed an extensive genetic map encompassing 7,730 markers over 2,784.2 cM. We appraised two architectural and seven fiber traits within six environments, identifying 58 QTLs, of which 49 demonstrated stability across these environments. These encompassed QTLs for traits such as lint percentage (LP), boll weight (BW), fiber strength (STRENGTH), seed index (SI), and micronaire (MIC), primarily located on chromosomes chr-A07, chr-D06, and chr-D07. Notably, chr-D07 houses a QTL region affecting SI, corroborated by multiple studies. Within this region, the genes BZIP043 and SEP2 were identified as pivotal, with SEP2 particularly showing augmented expression in developing ovules. These discoveries contribute significantly to marker-assisted selection, potentially elevating both the yield and quality of cotton fiber production. These findings provide valuable insights into marker-assisted breeding strategies, offering crucial information to enhance fiber yield and quality in cotton production.

Functional divergence of GhAP1.1 and GhFUL2 associated with flowering regulation in upland cotton (Gossypium hirsutum L.)

The AP1/FUL transcription factors are important for floral development, but the underlying molecular mechanisms remain unclear. In this study, we cloned and identified two AP1/FUL-like genes, GhAP1.1 and GhFUL2, in upland cotton, which is a commonly cultivated economically valuable crop. Sequence alignment and phylogenetic analysis indicated that GhAP1.1 and GhFUL2, which are encoded by genes in the AP1/FUL clade, have conserved N-terminal regions but diverse C-terminal domains. Quantitative real-time PCR analysis revealed that GhAP1.1 and GhFUL2 were expressed in the flower and root, and showed opposite expression patterns during shoot apical meristem development. The upregulated expression of GhAP1.1 in Arabidopsis did not result in significant changes to the flowering time or floral organ development, and the transcript levels of the florigen FT increased and those of LFY decreased. Overexpression of GhFUL2 in Arabidopsis delayed flowering and promoted bolting by decreasing FT and LFY transcript levels. Silencing GhFUL2 in cotton dramatically increased the expression of GhFT and GhAP1.3 and promoted flowering. Yeast two-hybrid and bimolecular fluorescence complementation assays indicated that GhAP1.1 could interact with the SVP homolog GhSVP2.2, whereas GhFUL2 formed heterodimers with GhSEP3/GhSEP4 homologs and GhSVP2.2. The present results demonstrated that the functional divergence of GhAP1.1 and GhFUL2, which involved changes in sequences and expression patterns, influenced the regulation of cotton flower development.

Genetic Diversity, QTL Mapping, and Marker-Assisted Selection Technology in Cotton (Gossypium spp.)

Cotton genetic resources contain diverse economically important traits that can be used widely in breeding approaches to create of high-yielding elite cultivars with superior fiber quality and adapted to biotic and abiotic stresses. Nevertheless, the creation of new cultivars using conventional breeding methods is limited by the cost and proved to be time consuming process, also requires a space to make field observations and measurements. Decoding genomes of cotton species greatly facilitated generating large-scale high-throughput DNA markers and identification of QTLs that allows confirmation of candidate genes, and use them in marker-assisted selection (MAS)-based breeding programs. With the advances of quantitative trait loci (QTL) mapping and genome-wide-association study approaches, DNA markers associated with valuable traits significantly accelerate breeding processes by replacing the selection with a phenotype to the selection at the DNA or gene level. In this review, we discuss the evolution and genetic diversity of cotton Gossypium genus, molecular markers and their types, genetic mapping and QTL analysis, application, and perspectives of MAS-based approaches in cotton breeding.

Development of EST-SSR Markers Linked to Flowering Candidate Genes in Elymus sibiricus L. Based on RNA Sequencing

Elymus sibiricus L. is an important cold-season grass with excellent cold and drought tolerance, good palatability, and nutrition. Flowering time is a key trait that affects forage and seed yield. Development of EST-SSR (expressed sequence tag simple sequence repeat) markers based on flowering genes contributes to the improvement of flowering traits. In the study, we detected 155 candidate genes related to flowering traits from 10,591 unigenes via transcriptome sequencing in early- and late-flowering genotypes. These candidate genes were mainly involved in the photoperiodic pathway, vernalization pathway, central integrator, and gibberellin pathway. A total of 125 candidate gene-based EST-SSRs were developed. Further, 15 polymorphic EST-SSRs closely associated to 13 candidate genes were used for genetic diversity and population structure analysis among 20 E. sibiricus accessions, including two contrasting panels (early-flowering and late-flowering). Among them, primer 28366, designed from heading date 3a (HD3a), effectively distinguished early- and late-flowering genotypes using a specifically amplified band of 175 bp. The polymorphic information content (PIC) value ranged from 0.12 to 0.48, with an average of 0.25. The unweighted pair group method analysis (UPGMA) cluster and structure analysis showed that the 20 E. sibiricus genotypes with similar flowering times tended to group together. These newly developed EST-SSR markers have the potential to be used for molecular markers assisted selection and germplasm evaluation of flowering traits in E. sibiricus.

Genome-wide analysis of the MADS-box gene family in polyploid cotton (Gossypium hirsutum) and in its diploid parental species (Gossypium arboreum and Gossypium raimondii)

The MADS-box gene family encodes transcription factors that share a highly conserved domain known to bind to DNA. Members of this family control various processes of development in plants, from root formation to fruit ripening. In this work, a survey of diploid (Gossypium raimondii and Gossypium arboreum) and tetraploid (Gossypium hirsutum) cotton genomes found a total of 147, 133 and 207 MADS-box genes, respectively, distributed in the MIKC, Mα, Mβ, Mγ, and Mδ subclades. A comparative phylogenetic analysis among cotton species, Arabidopsis, poplar and grapevine MADS-box homologous genes allowed us to evaluate the evolution of each MADS-box lineage in cotton plants and identify sequences within well-established subfamilies. Chromosomal localization and phylogenetic analysis revealed that G. raimondii and G. arboreum showed a conserved evolution of the MIKC subclade and a distinct pattern of duplication events in the Mα, Mγ and Mδ subclades. Additionally, G. hirsutum showed a combination of its parental subgenomes followed by a distinct evolutionary history including gene gain and loss in each subclade. qPCR analysis revealed the expression patterns of putative homologs in the AP1, AP3, AGL6, SEP4, AGL15, AG, AGL17, TM8, SVP, SOC and TT16 subfamilies of G. hirsutum. The identification of putative cotton orthologs is discussed in the light of evolution and gene expression data from other plants. This analysis of the MADS-box genes in Gossypium species opens an avenue to understanding the origin and evolution of each gene subfamily within diploid and polyploid species and paves the way for functional studies in cotton species.

Recent insights into cotton functional genomics: progress and future perspectives

Functional genomics has transformed from futuristic concept to well-established scientific discipline during the last decade. Cotton functional genomics promise to enhance the understanding of fundamental plant biology to systematically exploit genetic resources for the improvement of cotton fibre quality and yield, as well as utilization of genetic information for germplasm improvement. However, determining the cotton gene functions is a much more challenging task, which has not progressed at a rapid pace. This article presents a comprehensive overview of the recent tools and resources available with the major advances in cotton functional genomics to develop elite cotton genotypes. This effort ultimately helps to filter a subset of genes that can be used to assemble a final list of candidate genes that could be employed in future novel cotton breeding programme. We argue that next stage of cotton functional genomics requires the draft genomes refinement, re-sequencing broad diversity panels with the development of high-throughput functional genomics tools and integrating multidisciplinary approaches in upcoming cotton improvement programmes.

QTL mapping for flowering-time and photoperiod insensitivity of cotton Gossypium darwinii Watt

Most wild and semi-wild species of the genus Gossypium are exhibit photoperiod-sensitive flowering. The wild germplasm cotton is a valuable source of genes for genetic improvement of modern cotton cultivars. A bi-parental cotton population segregating for photoperiodic flowering was developed by crossing a photoperiod insensitive irradiation mutant line with its pre-mutagenesis photoperiodic wild-type G. darwinii Watt genotype. Individuals from the F2 and F3 generations were grown with their parental lines and F1 hybrid progeny in the long day and short night summer condition (natural day-length) of Uzbekistan to evaluate photoperiod sensitivity, i.e., flowering-time during the seasons 2008-2009. Through genotyping the individuals of this bi-parental population segregating for flowering-time, linkage maps were constructed using 212 simple-sequence repeat (SSR) and three cleaved amplified polymorphic sequence (CAPS) markers. Six QTLs directly associated with flowering-time and photoperiodic flowering were discovered in the F2 population, whereas eight QTLs were identified in the F3 population. Two QTLs controlling photoperiodic flowering and duration of flowering were common in both populations. In silico annotations of the flanking DNA sequences of mapped SSRs from sequenced cotton (G. hirsutum L.) genome database has identified several potential 'candidate' genes that are known to be associated with regulation of flowering characteristics of plants. The outcome of this research will expand our understanding of the genetic and molecular mechanisms of photoperiodic flowering. Identified markers should be useful for marker-assisted selection in cotton breeding to improve early flowering characteristics.

Characterization and Functional Analysis of PEBP Family Genes in Upland Cotton (Gossypium hirsutum L.)

Upland cotton (Gossypium hirsutum L.) is a naturally occurring photoperiod-sensitive perennial plant species. However, sensitivity to the day length was lost during domestication. The phosphatidylethanolamine-binding protein (PEBP) gene family, of which three subclades have been identified in angiosperms, functions to promote and suppress flowering in photoperiod pathway. Recent evidence indicates that PEBP family genes play an important role in generating mobile flowering signals. We isolated homologues of the PEBP gene family in upland cotton and examined their regulation and function. Nine PEBP-like genes were cloned and phylogenetic analysis indicated the genes belonged to four subclades (FT, MFT, TFL1 and PEBP). Cotton PEBP-like genes showed distinct expression patterns in relation to different cotton genotypes, photoperiod responsive and cultivar maturity. The GhFT gene expression of a semi-wild race of upland cotton were strongly induced under short day condition, whereas the GhPEBP2 gene expression was induced under long days. We also elucidated that GhFT but not GhPEBP2 interacted with FD-like bZIP transcription factor GhFD and promote flowering under both long- and short-day conditions. The present result indicated that GhPEBP-like genes may perform different functions. This work corroborates the involvement of PEBP-like genes in photoperiod response and regulation of flowering time in different cotton genotypes, and contributes to an improved understanding of the function of PEBP-like genes in cotton.

Characterization of the global transcriptome for cotton (Gossypium hirsutum L.) anther and development of SSR marker

Cotton is an important fiber plant, and it's attractive to elucidate the molecular mechanism of anther development due to the close relationship between the anther fertility and boll-setting, and also fiber yield. In the present paper, 47.2 million paired-end reads with average length of 82.87 bp from the anthers of TM-1 (Gossypium hirsutum L.), a genetic standard line, were generated through transcriptome sequencing, and 210,965 unigenes of more than 100 bp were obtained. BLAST, KEGG, COG, and GO analyses showed that the genes were enriched in the processes of transcription, translation, and post-translation as well as hormone signal transduction, the transcription factor families, and cell wall-related genes mainly participating in cell expansion and carbohydrate metabolism. Further analysis identified 11,153 potential SSRs. A suit of 5122 primer pair sequences were designed, and 82 of 300 randomly selected primer pairs produced reproducible amplicons that were polymorphic among 22 cotton accessions from G. hirsutum, Gossypium barbadense and Gossypium arboreum. The UPGMA clustering analysis further confirmed high quality and effectiveness of these novel SSR markers. The present study provided insights into the transcriptome profile of the cotton and established a public information platform for functional genomics and molecular breeding.

Genome-wide analysis of the WRKY gene family in cotton

WRKY proteins are major transcription factors involved in regulating plant growth and development. Although many studies have focused on the functional identification of WRKY genes, our knowledge concerning many areas of WRKY gene biology is limited. For example, in cotton, the phylogenetic characteristics, global expression patterns, molecular mechanisms regulating expression, and target genes/pathways of WRKY genes are poorly characterized. Therefore, in this study, we present a genome-wide analysis of the WRKY gene family in cotton (Gossypium raimondii and Gossypium hirsutum). We identified 116 WRKY genes in G. raimondii from the completed genome sequence, and we cloned 102 WRKY genes in G. hirsutum. Chromosomal location analysis indicated that WRKY genes in G. raimondii evolved mainly from segmental duplication followed by tandem amplifications. Phylogenetic analysis of alga, bryophyte, lycophyta, monocot and eudicot WRKY domains revealed family member expansion with increasing complexity of the plant body. Microarray, expression profiling and qRT-PCR data revealed that WRKY genes in G. hirsutum may regulate the development of fibers, anthers, tissues (roots, stems, leaves and embryos), and are involved in the response to stresses. Expression analysis showed that most group II and III GhWRKY genes are highly expressed under diverse stresses. Group I members, representing the ancestral form, seem to be insensitive to abiotic stress, with low expression divergence. Our results indicate that cotton WRKY genes might have evolved by adaptive duplication, leading to sensitivity to diverse stresses. This study provides fundamental information to inform further analysis and understanding of WRKY gene functions in cotton species.

Upland cotton gene GhFPF1 confers promotion of flowering time and shade-avoidance responses in Arabidopsis thaliana

Extensive studies on floral transition in model species have revealed a network of regulatory interactions between proteins that transduce and integrate developmental and environmental signals to promote or inhibit the transition to flowering. Previous studies indicated FLOWERING PROMOTING FACTOR 1 (FPF1) gene was involved in the promotion of flowering, but the molecular mechanism was still unclear. Here, FPF1 homologous sequences were screened from diploid Gossypium raimondii L. (D-genome, n = 13) and Gossypium arboreum L. genome (A-genome, n = 13) databases. Orthologous genes from the two species were compared, suggesting that distinctions at nucleic acid and amino acid levels were not equivalent because of codon degeneracy. Six FPF1 homologous genes were identified from the cultivated allotetraploid Gossypium hirsutum L. (AD-genome, n = 26). Analysis of relative transcripts of the six genes in different tissues revealed that this gene family displayed strong tissue-specific expression. GhFPF1, encoding a 12.0-kDa protein (Accession No: KC832319) exerted more transcripts in floral apices of short-season cotton, hinting that it could be involved in floral regulation. Significantly activated APETALA 1 and suppressed FLOWERING LOCUS C expression were induced by over-expression of GhFPF1 in the Arabidopsis Columbia-0 ecotype. In addition, transgenic Arabidopsis displayed a constitutive shade-avoiding phenotype that is characterized by long hypocotyls and petioles, reduced chlorophyll content, and early flowering. We propose that GhFPF1 may be involved in flowering time control and shade-avoidance responses.

Cloning and characterization of a FLO/LFY ortholog in Gossypium hirsutum L

KEY MESSAGE

GhLFY was cloned from G. hirsutum L. Its expression, subcellular localization, and function were analyzed, as well as the in vivo regulation of GhLFY by the MADS-box protein SOC1 (GhSOC1).

ABSTRACT

Flowering is a very important phase during which plants produce the organs for sexual reproduction. The FLORICAULA/LEAFY (FLO/LFY) homologs play a major role in the initiation of flowering. To understand the mechanism of the transition from the vegetative to reproductive phases in Upland cotton (Gossypium hirsutum L.), we isolated a candidate LFY gene from G. hirsutum L. (GhLFY) that showed a high degree of similarity to other plant homologs of FLO/LFY. qPCR analysis showed that GhLFY was highly expressed in the shoot apex, with substantial upregulation at the third true leaf expansion stage during floral bud differentiation. Subcellular localization studies revealed GhLFY localization in the nucleus. Ectopic expression of the GhLFY coding region in Arabidopsis resulted in early flowering. The expression of the GhLFY coding region under the control of the 35S promoter complemented the lfy-5 mutation in transgenic Arabidopsis lfy-5 mutant plants. Furthermore, a chromatin immunoprecipitation assay revealed that GhLFY may function downstream of GhSOC1 during the initiation of flowering in G. hirsutum L. GhLFY was likely to be regulated by GhSOC1, which binds to the LFY promoter in Arabidopsis. These results suggest that GhLFY is a FLO/LFY ortholog that may be involved in controlling flowering time and floral development.

Gene silencing of BnTT10 family genes causes retarded pigmentation and lignin reduction in the seed coat of Brassica napus

Yellow-seed (i.e., yellow seed coat) is one of the most important agronomic traits of Brassica plants, which is correlated with seed oil and meal qualities. Previous studies on the Brassicaceae, including Arabidopsis and Brassica species, proposed that the seed-color trait is correlative to flavonoid and lignin biosynthesis, at the molecular level. In Arabidopsis thaliana, the oxidative polymerization of flavonoid and biosynthesis of lignin has been demonstrated to be catalyzed by laccase 15, a functional enzyme encoded by the AtTT10 gene. In this study, eight Brassica TT10 genes (three from B. napus, three from B. rapa and two from B. oleracea) were isolated and their roles in flavonoid oxidation/polymerization and lignin biosynthesis were investigated. Based on our phylogenetic analysis, these genes could be divided into two groups with obvious structural and functional differentiation. Expression studies showed that Brassica TT10 genes are active in developing seeds, but with differential expression patterns in yellow- and black-seeded near-isogenic lines. For functional analyses, three black-seeded B. napus cultivars were chosen for transgenic studies. Transgenic B. napus plants expressing antisense TT10 constructs exhibited retarded pigmentation in the seed coat. Chemical composition analysis revealed increased levels of soluble proanthocyanidins, and decreased extractable lignin in the seed coats of these transgenic plants compared with that of the controls. These findings indicate a role for the Brassica TT10 genes in proanthocyanidin polymerization and lignin biosynthesis, as well as seed coat pigmentation in B. napus.

Characterization of expressed sequence tags from developing fibers of Gossypium barbadense and evaluation of insertion-deletion variation in tetraploid cultivated cotton species

Background

Cotton is the leading fiber crop worldwide. Gossypium barbadense is an important species of cotton because of its extra-long staple fibers with superior luster and silkiness. However, a systematic analysis and utilization of cDNA sequences from G. barbadense fiber development remains understudied.

Results

A total of 21,079 high quality sequences were generated from two non-normalized cDNA libraries prepared by using a mixture of G. barbadense Hai7124 fibers and ovules. After assembly processing, a set of 8,653 unigenes were obtained. Of those, 7,786 were matched to known proteins and 7,316 were assigned to functional categories. The molecular functions of these unigenes were mostly related to binding and catalytic activity, and carbohydrate, amino acid, and energy metabolisms were major contributors among the subsets of metabolism. Sequences comparison between G. barbadense and G. hirsutum revealed that 8,245 unigenes from G. barbadense were detected the similarity with those released publicly in G. hirsutum, however, the remaining 408 sequences had no hits against G. hirsutum unigenes database. Furthermore, 13,275 putative ESTs InDels loci involved in the orthologous and/or homoeologous differences between/within G. barbadense and G. hirsutum were discovered by in silico analyses, and 2,160 InDel markers were developed by ESTs with more than five insertions or deletions. By gel electrophoresis combined with sequencing verification, 71.11% candidate InDel loci were reconfirmed orthologous and/or homoeologous loci polymorphisms using G. hirsutum acc TM-1 and G. barbadense cv Hai7124. Blastx result showed among 2,160 InDel loci, 81 with significant function similarity with known genes associated with secondary wall synthesis process, indicating the important roles in fiber quality in tetraploid cultivated cotton species.

Conclusion

Sequence comparisons and InDel markers development will lay the groundwork for promoting the identification of genes related to superior agronomic traits, genetic differentiation and comparative genomic studies between G. hirsutum and G. barbadense.

Transcriptome profiling analysis reveals that flavonoid and ascorbate-glutathione cycle are important during anther development in Upland cotton

BACKGROUND

Previous transcriptome profiling studies have investigated the molecular mechanisms of pollen and anther development, and identified many genes involved in these processes. However, only 51 anther ESTs of Upland cotton (Gossypium hirsutum) were found in NCBI and there have been no reports of transcriptome profiling analyzing anther development in Upland cotton, a major fiber crop in the word.

METHODOLOGY/PRINCIPAL FINDING

Ninety-eight hundred and ninety-six high quality ESTs were sequenced from their 3'-ends and assembled into 6,643 unigenes from a normalized, full-length anther cDNA library of Upland cotton. Combined with previous sequenced anther-related ESTs, 12,244 unigenes were generated as the reference genes for digital gene expression (DGE) analysis. The DGE was conducted on anthers that were isolated at tetrad pollen (TTP), uninucleate pollen (UNP), binucleate pollen (BNP) and mature pollen (MTP) periods along with four other tissues, i.e., roots (RO), stems (ST), leaves (LV) and embryos (EB). Through transcriptome profiling analysis, we identified 1,165 genes that were enriched at certain anther development periods, and many of them were involved in starch and sucrose metabolism, pentose and glucuronate interconversion, flavonoid biosynthesis, and ascorbate and aldarate metabolism.

CONCLUSIONS/SIGNIFICANCE

We first generated a normalized, full-length cDNA library from anthers and performed transcriptome profiling analysis of anther development in Upland cotton. From these results, 10,178 anther expressed genes were identified, among which 1,165 genes were stage-enriched in anthers. And many of these stage-enriched genes were involved in some important processes regulating anther development.