Fine mapping and identification of the fuzzless gene GaFzl in DPL972 (Gossypium arboreum)

The genetic basis of leaf hair development in upland cotton (Gossypium hirsutum)

Trichomes, which originate from the epidermal cell of aerial organs, provide plants with defense and secretion functions. Although numerous genes have been implicated in trichome development, the molecular mechanisms underlying trichome cell formation in plants remain incompletely understood. Here, we using genome-wide association study (GWAS) across 1037 diverse accessions in upland cotton (Gossypium hirsutum) to identify three loci associated with leaf pubescence (hair) amount, located on chromosome A06 (LPA1), A08 (LPA2) and A11 (LPA3), respectively. GhHD1, a previously characterized candidate gene, was identified on LPA1 and encodes an HD-Zip transcription factor. For LPA2 and LPA3, we identified two candidate genes, GhGIR1 and GhGIR2, both encoding proteins with WD40 and RING domains that act as inhibitors of leaf hair formation. Expression analysis revealed that GhHD1 was predominantly expressed in hairy accessions, whereas GhGIR1 and GhGIR2 were expressed in hairless accessions. Silencing GhHD1 or overexpressing GhGIR1 in hairy accessions induced in a hairless phenotype, whereas silencing GhGIR2 in hairless accessions resulted in a hairy phenotype. We also demonstrated that GhHD1 interact with both GhGIR1 and GhGIR2, and GhGIR1 can interact with GhGIR2. Further investigation indicated that GhHD1 functions as a transcriptional activator, binding to the promoters of the GhGIR1 and GhGIR2 to active their expression, whereas GhGIR1 and GhGIR2 can suppress the transcriptional activation of GhHD1. Our findings shed light on the intricate regulatory network involving GhHD1, GhGIR1 and GhGIR2 in the initiation and development of plant epidermal hairs in cotton.

Genome-Wide and Expression Pattern Analysis of the DVL Gene Family Reveals GhM_A05G1032 Is Involved in Fuzz Development in G. hirsutum

DVL is one of the small polypeptides which plays an important role in regulating plant growth and development, tissue differentiation, and organ formation in the process of coping with stress conditions. So far, there has been no comprehensive analysis of the expression profile and function of the cotton DVL gene. According to previous studies, a candidate gene related to the development of fuzz was screened, belonging to the DVL family, and was related to the development of trichomes in Arabidopsis thaliana. However, the comprehensive identification and systematic analysis of DVL in cotton have not been conducted. In this study, we employed bioinformatics approaches to conduct a novel analysis of the structural characteristics, phylogenetic tree, gene structure, expression pattern, evolutionary relationship, and selective pressure of the DVL gene family members in four cotton species. A total of 117 DVL genes were identified, including 39 members in G. hirsutum. Based on the phylogenetic analysis, the DVL protein sequences were categorized into five distinct subfamilies. Additionally, we successfully mapped these genes onto chromosomes and visually represented their gene structure information. Furthermore, we predicted the presence of cis-acting elements in DVL genes in G. hirsutum and characterized the repeat types of DVL genes in the four cotton species. Moreover, we computed the Ka/Ks ratio of homologous genes across the four cotton species and elucidated the selective pressure acting on these homologous genes. In addition, we described the expression patterns of the DVL gene family using RNA-seq data, verified the correlation between GhMDVL3 and fuzz development through VIGS technology, and found that some DVL genes may be involved in resistance to biotic and abiotic stress conditions through qRT-PCR technology. Furthermore, a potential interaction network was constructed by WGCNA, and our findings demonstrated the potential of GhM_A05G1032 to interact with numerous genes, thereby playing a crucial role in regulating fuzz development. This research significantly contributed to the comprehension of DVL genes in upland cotton, thereby establishing a solid basis for future investigations into the functional aspects of DVL genes in cotton.

GoSTR, a negative modulator of stem trichome formation in cotton

Trichomes, the outward projection of plant epidermal tissue, provide an effective defense against stress and insect pests. Although numerous genes have been identified to be involved in trichome development, the molecular mechanism for trichome cell fate determination is not well enunciated. Here, we reported GoSTR functions as a master repressor for stem trichome formation, which was isolated by map-based cloning based on a large F2 segregating population derived from a cross between TM-1 (pubescent stem) and J220 (smooth stem). Sequence alignment revealed a critical G-to-T point mutation in GoSTR's coding region that converted codon 2 from GCA (Alanine) to TCA (Serine). This mutation occurred between the majority of Gossypium hirsutum with pubescent stem (GG-haplotype) and G. barbadense with glabrous stem (TT-haplotype). Silencing of GoSTR in J220 and Hai7124 via virus-induced gene silencing resulted in the pubescent stems but no visible change in leaf trichomes, suggesting stem trichomes and leaf trichomes are genetically distinct. Yeast two-hybrid assay and luciferase complementation imaging assay showed GoSTR interacts with GoHD1 and GoHOX3, two key regulators of trichome development. Comparative transcriptomic analysis further indicated that many transcription factors such as GhMYB109, GhTTG1, and GhMYC1/GhDEL65 which function as positive regulators of trichomes were significantly upregulated in the stem from the GoSTR-silencing plant. Taken together, these results indicate that GoSTR functions as an essential negative modulator of stem trichomes and its transcripts will greatly repress trichome cell differentiation and growth. This study provided valuable insights for plant epidermal hair initiation and differentiation research.

Combined QTL-sequencing, linkage mapping, and RNA-sequencing identify candidate genes and KASP markers for low-temperature germination in Oryza sativa L. ssp. Japonica

MAIN CONCLUSION

Through QTL-seq, QTL mapping and RNA-seq, six candidate genes of qLTG9 can be used as targets for cold tolerance functional characterization, and six KASP markers can be used for marker-assisted breeding to improve the germination ability of japonica rice at low temperature. The development of direct-seeded rice at high latitudes and altitudes depends on the seed germination ability of rice under a low-temperature environment. However, the lack of regulatory genes for low-temperature germination has severely limited the application of genetics in improving the breeds. Here, we used cultivars DN430 and DF104 with significantly different low-temperature germination (LTG) and 460 F_2:3 progeny derived from them to identify LTG regulators by combining QTL-sequencing, linkage mapping, and RNA-sequencing. The QTL-sequencing mapped qLTG9 within a physical interval of 3.4 Mb. In addition, we used 10 Kompetitive allele-specific PCR (KASP) markers provided by the two parents, and qLTG9 was optimized from 3.4 Mb to a physical interval of 397.9 kb and accounted for 20.4% of the phenotypic variation. RNA-sequencing identified qLTG9 as eight candidate genes with significantly different expression within the 397.9 kb interval, six of which possessed SNPs on the promoter and coding regions. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) completely validated the results of these six genes in RNA-sequencing. Subsequently, six non-synonymous SNPs were designed using variants in the coding region of these six candidates. Genotypic analysis of these SNPs in 60 individuals with extreme phenotypes indicated these SNPs determined the differences in cold tolerance between parents. The six candidate genes of qLTG9 and the six KASP markers could be used together for marker-assisted breeding to improve LTG.

A combinatorial strategy to identify various types of QTLs for quantitative traits using extreme phenotype individuals in an F2 population

Theoretical and applied studies demonstrate the difficulty of detecting extremely over-dominant and small-effect genes for quantitative traits via bulked segregant analysis (BSA) in an F2 population. To address this issue, we proposed an integrated strategy for mapping various types of quantitative trait loci (QTLs) for quantitative traits via a combination of BSA and whole-genome sequencing. In this strategy, the numbers of read counts of marker alleles in two extreme pools were used to predict the numbers of read counts of marker genotypes. These observed and predicted numbers were used to construct a new statistic, Gw, for detecting quantitative trait genes (QTGs), and the method was named dQTG-seq1. This method was significantly better than existing BSA methods. If the goal was to identify extremely over-dominant and small-effect genes, another reserved DNA/RNA sample from each extreme phenotype F2 plant was sequenced, and the observed numbers of marker alleles and genotypes were used to calculate Gw to detect QTGs; this method was named dQTG-seq2. In simulated and real rice dataset analyses, dQTG-seq2 could identify many more extremely over-dominant and small-effect genes than BSA and QTL mapping methods. dQTG-seq2 may be extended to other heterogeneous mapping populations. The significance threshold of Gw in this study was determined by permutation experiments. In addition, a handbook for the R software dQTG.seq, which is available at https://cran.r-project.org/web/packages/dQTG.seq/index.html, has been provided in the supplemental materials for the users' convenience. This study provides a new strategy for identifying all types of QTLs for quantitative traits in an F2 population.

Genome-wide identification and expression analysis of GL2-interacting-repressor (GIR) genes during cotton fiber and fuzz development

GL2-interacting-repressor (GIR) family members may contribute to fiber/fuzz formation via a newly discovered unique pathway in Gossypium arboreum. There are similarities between cotton fiber development and the formation of trichomes and root hairs. The GL2-interacting-repressors (GIRs) are crucial regulators of root hair and trichome formation. The GaFzl gene, annotated as GaGIR1, is negatively associated with trichome development and fuzz initiation. However, there is relatively little available information regarding the other GIR genes in cotton, especially regarding their effects on cotton fiber development. In this study, 21 GIR family genes were identified in the diploid cotton species Gossypium arboreum; these genes were divided into three groups. The GIR genes were characterized in terms of their phylogenetic relationships, structures, chromosomal distribution and evolutionary dynamics. These GIR genes were revealed to be unequally distributed on 12 chromosomes in the diploid cotton genome, with no GIR gene detected on Ga06. The cis-acting elements in the promoter regions were predicted to be responsive to light, phytohormones, defense activities and stress. The transcriptomic data and qRT-PCR results revealed that most GIR genes were not differentially expressed between the wild-type control and the fuzzless mutant line. Moreover, 14 of 21 family genes were expressed at high levels, indicating these genes may play important roles during fiber development and fuzz formation. Furthermore, Ga01G0231 was predominantly expressed in root samples, suggestive of a role in root hair formation rather than in fuzz initiation and development. The results of this study have enhanced our understanding of the GIR genes and their potential utility for improving cotton fiber through breeding.

Genome-Wide Analysis of SRNF Genes in Gossypium hirsutum Reveals the Role of GhSRNF18 in Primary Root Growth

Root systems are instrumental for water and nutrient uptake and the anchorage of plants in the soil. Root regulating GL2-interacting repressors (GIRs) contain a Short RING-like Zinc-Finger (SRNF) domain, but there has been no comprehensive characterization about this gene family in any plant species. Here, we renamed the GIR-like proteins as SRNF proteins due to their conserved domain and identified 140 SRNF genes from 16 plant species including 24 GhSRNF genes in Gossypium hirsutum. Phylogenetic analysis of the SRNFs revealed both similarities and divergences between five subfamilies. Notably, synteny analysis revealed that polyploidization and whole-genome duplication contribute to the expansion of the GhSRNF gene family. Various cis-acting regulatory elements were shown to be pertinent to light, phytohormone, defense responsive, and meristem regulation. Furthermore, GhSRNF2/15 were predominantly expressed in root, whereas the expression of GhSRNF18 is positively correlated with the primary root (PR) length in G. hirsutum, quantified by quantitative real-time PCR (qRT-PCR). Over-expression of GhSRNF18 in Arabidopsis and virus-induced gene silencing (VIGS) of GhSRNF18 in G. hirsutum has revealed the role of GhSRNF18 in PR growth. The over-expression of GhSRNF18 in Arabidopsis resulted in an increase of meristematic activities and auxin accumulations in PRs, which were consistent with the transcriptomic data. Our results suggested that GhSRNF18 positively regulates PR growth. This study increased our understanding of the SRNF gene family in plants and provided a novel rationale for the further investigation of cotton root morphogenesis regulated by the GhSRNFs.

Combining QTL-seq and linkage mapping to fine map a candidate gene in qCTS6 for cold tolerance at the seedling stage in rice

BACKGROUND

Cold stress caused by low temperatures is an important factor restricting rice production. Identification of cold-tolerance genes that can stably express in cold environments is crucial for molecular rice breeding.

RESULTS

In this study, we employed high-throughput quantitative trait locus sequencing (QTL-seq) analyses in a 460-individual F2:3 mapping population to identify major QTL genomic regions governing cold tolerance at the seedling stage in rice. A novel major QTL (qCTS6) controlling the survival rate (SR) under low-temperature conditions of 9°C/10 days was mapped on the 2.60-Mb interval on chromosome 6. Twenty-seven single-nucleotide polymorphism (SNP) markers were designed for the qCST6 region based on re-sequencing data, and local QTL mapping was conducted using traditional linkage analysis. Eventually, we mapped qCTS6 to a 96.6-kb region containing 13 annotated genes, of which seven predicted genes contained 13 non-synonymous SNP loci. Quantitative reverse transcription PCR analysis revealed that only Os06g0719500, an OsbZIP54 transcription factor, was strongly induced by cold stress. Haplotype analysis confirmed that +376 bp (T>A) in the OsbZIP54 coding region played a key role in regulating cold tolerance in rice.

CONCLUSION

We identified OsbZIP54 as a novel regulatory gene associated with rice cold-responsive traits, with its Dongfu-104 allele showing specific cold-induction expression serving as an important molecular variation for rice improvement. This result is expected to further exploration of the genetic mechanism of rice cold tolerance at the seedling stage and improve cold tolerance in rice varieties by marker-assisted selection.

Mapping-by-sequencing the locus of EMS-induced mutation responsible for tufted-fuzzless seed phenotype in cotton

Cotton fiber mutants are valuable resources for studying functions of altered genes and their roles in fiber development. The n₄^t is a recessive tufted-fuzzless seed mutant created through chemical mutagenesis with ethyl methanesulfonate. Genetic analysis indicated that the tufted-fuzzless phenotype is controlled by a single recessive locus. In this study, we developed an F₂ population of 602 progeny plants and sequenced the genomes of the parents and two DNA bulks from F₂ progenies showing the mutant phenotype. We identified DNA sequence variants between the tufted-fuzzless mutant and wild type by aligning the sequence reads to the reference TM-1 genome and designed subgenome-specific SNP markers. We mapped the n₄^t locus on chromosome D04 within a genomic interval of about 411 kb. In this region, seven genes showed significant differential expression between the tufted-fuzzless mutant and wild type. Possible candidate genes are discussed in this study. The utilization of the n₄^t mutant along with other fiber mutants will facilitate our understanding of the molecular mechanisms of cotton fiber cell growth and development.

Large-fragment insertion activates gene GaFZ (Ga08G0121) and is associated with the fuzz and trichome reduction in cotton (Gossypium arboreum)

Cotton seeds are typically covered by lint and fuzz fibres. Natural 'fuzzless' mutants are an ideal model system for identifying genes that regulate cell initiation and elongation. Here, using a genome-wide association study (GWAS), we identified a ~ 6.2 kb insertion, larINDEL_FZ , located at the end of chromosome 8, composed of a ~ 5.0 kb repetitive sequence and a ~ 1.2 kb fragment translocated from chromosome 12 in fuzzless Gossypium arboreum. The presence of larINDEL_FZ was associated with a fuzzless seed and reduced trichome phenotypes in G. arboreum. This distant insertion was predicted to be an enhancer, located ~ 18 kb upstream of the dominant-repressor GaFZ (Ga08G0121). Ectopic overexpression of GaFZ in Arabidopsis thaliana and G. hirsutum suggested that GaFZ negatively modulates fuzz and trichome development. Co-expression and interaction analyses demonstrated that GaFZ might impact fuzz fibre/trichome development by repressing the expression of genes in the very-long-chain fatty acid elongation pathway. Thus, we identified a novel regulator of fibre/trichome development while providing insights into the importance of noncoding sequences in cotton.

Weighted Gene Co-Expression Network Analysis Reveals Hub Genes Contributing to Fuzz Development in Gossypium arboreum

Fuzzless mutants are ideal materials to decipher the regulatory network and mechanism underlying fuzz initiation and formation. In this study, we utilized two Gossypium arboreum accessions differing in fuzz characteristics to explore expression pattern differences and discriminate genes involved in fuzz development using RNA sequencing. Gene ontology (GO) analysis was conducted and found that DEGs were mainly enriched in the regulation of transcription, metabolic processes and oxidation–reduction-related processes. Weighted gene co-expression network analysis discerned the MEmagenta module highly associated with a fuzz/fuzzless trait, which included a total of 50 hub genes differentially expressed between two materials. GaFZ, which negatively regulates trichome and fuzz formation, was found involved in MEmagenta cluster1. In addition, twenty-eight hub genes in MEmagenta cluster1 were significantly up-regulated and expressed in fuzzless mutant DPL972. It is noteworthy that Ga04G1219 and Ga04G1240, which, respectively, encode Fasciclin-like arabinogalactan protein 18(FLA18) and transport protein, showed remarkable differences of expression level and implied that they may be involved in protein glycosylation to regulate fuzz formation and development. This module and hub genes identified in this study will provide new insights on fiber and fuzz formation and be useful for the molecular design breeding of cotton genetic improvement.

Identification of Candidate Genes Conferring Cold Tolerance to Rice (Oryza sativa L.) at the Bud-Bursting Stage Using Bulk Segregant Analysis Sequencing and Linkage Mapping

Low-temperature tolerance during the bud-bursting stage is an important characteristic of direct-seeded rice. The identification of cold-tolerance quantitative trait loci (QTL) in species that can stably tolerate cold environments is crucial for the molecular breeding of rice with such traits. In our study, high-throughput QTL-sequencing analyses were performed in a 460-individual F_{2 : 3} mapping population to identify the major QTL genomic regions governing cold tolerance at the bud-bursting (CTBB) stage in rice. A novel major QTL, qCTBB9, which controls seed survival rate (SR) under low-temperature conditions of 5°C/9 days, was mapped on the 5.40-Mb interval on chromosome 9. Twenty-six non-synonymous single-nucleotide polymorphism (nSNP) markers were designed for the qCTBB9 region based on re-sequencing data and local QTL mapping conducted using traditional linkage analysis. We mapped qCTBB9 to a 483.87-kb region containing 58 annotated genes, among which six predicted genes contained nine nSNP loci. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed that only Os09g0444200 was strongly induced by cold stress. Haplotype analysis further confirmed that the SNP 1,654,225 bp in the Os09g0444200 coding region plays a key role in regulating the cold tolerance of rice. These results suggest that Os09g0444200 is a potential candidate for qCTBB9. Our results are of great significance to explore the genetic mechanism of rice CTBB and to improve the cold tolerance of rice varieties by marker-assisted selection.

Genetic mapping and transcriptomic characterization of a new fuzzless-tufted cottonseed mutant

Fiber mutants are unique and valuable resources for understanding the genetic and molecular mechanisms controlling initiation and development of cotton fibers that are extremely elongated single epidermal cells protruding from the seed coat of cottonseeds. In this study, we reported a new fuzzless-tufted cotton mutant (Gossypium hirsutum) and showed that fuzzless-tufted near-isogenic lines (NILs) had similar agronomic traits and a higher ginning efficiency compared to their recurrent parents with normal fuzzy seeds. Genetic analysis revealed that the mutant phenotype is determined by a single incomplete dominant locus, designated N5. The mutation was fine mapped to an approximately 250-kb interval containing 33 annotated genes using a combination of bulked segregant sequencing, SNP chip genotyping, and fine mapping. Comparative transcriptomic analysis using 0-6 days post-anthesis (dpa) ovules from NILs segregating for the phenotypes of fuzzless-tufted (mutant) and normal fuzzy cottonseeds (wild-type) uncovered candidate genes responsible for the mutant phenotype. It also revealed that the flanking region of the N5 locus is enriched with differentially expressed genes (DEGs) between the mutant and wild-type. Several of those DEGs are members of the gene families with demonstrated roles in cell initiation and elongation, such as calcium-dependent protein kinase and expansin. The transcriptome landscape of the mutant was significantly reprogrammed in the 6 dpa ovules and, to a less extent, in the 0 dpa ovules, but not in the 2 and 4 dpa ovules. At both 0 and 6 dpa, the reprogrammed mutant transcriptome was mainly associated with cell wall modifications and transmembrane transportation, while transcription factor activity was significantly altered in the 6 dpa mutant ovules. These results imply a similar molecular basis for initiation of lint and fuzz fibers despite certain differences.

A Retrotransposon Insertion in GhMML3_D12 Is Likely Responsible for the Lintless Locus li3 of Tetraploid Cotton

Cotton (Gossypium) seed fibers can be divided into lint (long) or fuzz (very short). Using fiberless (fuzzless-lintless) mutants, the lint initiation gene Li₃ was identified by map-based cloning. The gene is an R2R3-MYB transcription factor located on chromosome D12 (GhMML3_D12). Sequence analysis revealed that li₃ is a loss-of-function allele containing a retrotransposon insertion in the second exon that completely blocks the gene’s expression. The genetic loci n₂ and n₃ underlying the recessive fuzzless phenotype in Gossypium hirsutum were also mapped. The genomic location of n₃ overlapped with that of the dominant fuzzless locus N₁, and n₃ appeared to be a loss-of-function allele caused by a single nucleotide polymorphism (SNP) mutation in the coding region of GhMML3_A12. The n₂ allele was found to be co-located with li₃ and originated from G. babardense. n₂ and li₃ are possibly the multiple alleles of the GhMML3_D12 gene. Genetic analysis showed that Li₃ and N₃ are a pair of homologs with additive effects for the initiation of fibers (fuzz or lint). In addition, the presence of another locus was speculated, and it appeared to show an inhibitory effect on the expression of GhMML3. These findings provide new information about the genetic factors affecting the initiation of fibers in cotton.

Elucidation of sequence polymorphism in fuzzless-seed cotton lines

Most commercially produced cotton cultivars have two types of fibers on the seed coat, short fuzz and long lint. Lint fiber is used in the textile industry, while fuzz is considered an undesirable trait. Both types of fibers are believed to be controlled by the same regulators; however, their mechanisms of actions are still obscure. Cotton fiber mutants provide an excellent system to study the genes that regulate fiber development. Here we described four uncharacterized and three previously reported cotton mutants with fuzzless seed phenotypes. To evaluate whether or not the genes previously associated with fuzzless seed phenotypes have mutations we sequenced whole genomic DNA of seven mutants and wild type varieties. We identified multiple polymorphic changes among the tested genes. Non-synonymous SNPs in the coding region of the MML3-A gene was common in the six mutant lines tested in this study, showing both dominant and recessive fuzzless phenotypes. We have mapped the locus of the causative mutation for one of the uncharacterized fuzzless lines using an F₂ population that originated from a cross between the dominant fuzzless mutant and a wild type. Further, we have clarified the current knowledge about the causative n₂ mutations by analyzing the sequence data and previously reported mapping data. The key genes and possible mechanisms of fiber differentiation are discussed in this study.

Transcriptome Analysis Reveals a Gene Expression Pattern Associated with Fuzz Fiber Initiation Induced by High Temperature in Gossypium barbadense

Gossypium barbadense is an important source of natural textile fibers, as is Gossypium hirsutum. Cotton fiber development is often affected by various environmental factors, such as abnormal temperature. However, little is known about the underlying mechanisms of temperature regulating the fuzz fiber initiation. In this study, we reveal that high temperatures (HT) accelerate fiber development, improve fiber quality, and induced fuzz initiation of a thermo-sensitive G. barbadense variety L7009. It was proved that fuzz initiation was inhibited by low temperature (LT), and 4 dpa was the stage most susceptible to temperature stress during the fuzz initiation period. A total of 43,826 differentially expressed genes (DEGs) were identified through comparative transcriptome analysis. Of these, 9667 were involved in fiber development and temperature response with 901 transcription factor genes and 189 genes related to plant hormone signal transduction. Further analysis of gene expression patterns revealed that 240 genes were potentially involved in fuzz initiation induced by high temperature. Functional annotation revealed that the candidate genes related to fuzz initiation were significantly involved in the asparagine biosynthetic process, cell wall biosynthesis, and stress response. The expression trends of sixteen genes randomly selected from the RNA-seq data were almost consistent with the results of qRT-PCR. Our study revealed several potential candidate genes and pathways related to fuzz initiation induced by high temperature. This provides a new view of temperature-induced tissue and organ development in Gossypium barbadense.

Genetic Identification and Transcriptome Analysis of Lintless and Fuzzless Traits in Gossypium arboreum L

Cotton fibres, as single cells arising from the seed coat, can be classified as lint and fuzz according to their final length. Gossypium arboreum is a cultivated diploid cotton species and a potential donor of the A subgenome of the more widely grown tetraploid cottons. In this study, we performed genetic studies on one lintless and seven fuzzless G. arboreum accessions. Through association and genetic linkage analyses, a recessive locus on Chr06 containing GaHD-1 was found to be the likely gene underlying the lintless trait. GaHD-1 carried a mutation at a splicing acceptor site that resulted in alternative splicing and a deletion of 247 amino acid from the protein. The regions containing GaGIR1 and GaMYB25-like were found to be associated with fuzz development in G. arboreum, with the former being the major contributor. Comparative transcriptome analyses using 0-5 days post-anthesis (dpa) ovules from lintless, fuzzless, and normal fuzzy seed G. arboreum accessions revealed gene modules and hub genes potentially important for lint and fuzz initiation and development. Three significant modules and 26 hub genes associated with lint fibre initiation were detected by weighted gene co-expression network analysis. Similar analyses identified three vital modules and 10 hub genes to be associated with fuzz development. The findings in this study contribute to understanding the complex molecular mechanism(s) regulating fibre initiation and development and indicate that G. arboreum may have fibre developmental pathways different from tetraploid cotton. It also provides candidate genes for further investigation into modifying fibre development in G. arboreum.