Synergistic interplay of redox homeostasis and polysaccharide synthesis promotes cotton fiber elongation.

Cell polarity is the foundation of cell development and tissue morphogenesis. The investigation of polarized growth provides opportunities to gain profound insights into morphogenesis and tissue functionality in organisms. Currently, there are still many mysteries surrounding the mechanisms that regulate polarized cell growth. Cotton fiber cells serve as an excellent model for studying polarized growth, and provide important clues for unraveling the molecular mechanisms, signaling pathways, and regulatory networks of polarized growth. In this study, we characterized two functional genes, GhMDHAR1AT/DT and GhDHAR2AT/DT with predominant expression during fiber elongation. Loss of function of both genes contributed to a significant increase in fiber length. Transcriptomic data revealed up-regulated expression of antioxidant genes in CRISPR mutant lines, along with delayed expression of secondary wall-related genes and temporally prolonged expression of primary wall-related genes. Experimental evidence demonstrated that the increase in GSH content and glutathione peroxidase (GPX) enzyme activity led to enhanced total antioxidant capacity (T-AOC), resulting in reduced H2O2 levels, which contributed to the extension of fiber elongation stage in CRISPR mutant lines. Moreover, the increased polysaccharide synthesis in CRISPR mutant lines was found to provide an abundant supply of raw materials for fiber cell wall elongation, suggesting that synergistic interplay between redox homeostasis and polysaccharide synthesis in fiber cells may facilitate cell wall remodeling and fiber elongation. This study provides valuable insights for deciphering the mechanisms of cell polarized growth and improving cotton fiber quality.

Genome-wide chromatin accessibility landscape and dynamics of transcription factor networks during ovule and fiber development in cotton.

BACKGROUND: The development of cotton fiber is regulated by the orchestrated binding of regulatory proteins to cis-regulatory elements associated with developmental genes. The cis-trans regulatory dynamics occurred throughout the course of cotton fiber development are elusive. Here we generated genome-wide high-resolution DNase I hypersensitive sites (DHSs) maps to understand the regulatory mechanisms of cotton ovule and fiber development. RESULTS: We generated DNase I hypersensitive site (DHS) profiles from cotton ovules at 0 and 3 days post anthesis (DPA) and fibers at 8, 12, 15, and 18 DPA. We obtained a total of 1185 million reads and identified a total of 199,351 DHSs through ~ 30% unique mapping reads. It should be noted that more than half of DNase-seq reads mapped multiple genome locations and were not analyzed in order to achieve a high specificity of peak profile and to avoid bias from repetitive genomic regions. Distinct chromatin accessibilities were observed in the ovules (0 and 3 DPA) compared to the fiber elongation stages (8, 12, 15, and 18 DPA). Besides, the chromatin accessibility during ovules was particularly elevated in genomic regions enriched with transposable elements (TEs) and genes in TE-enriched regions were involved in ovule cell division. We analyzed cis-regulatory modules and revealed the influence of hormones on fiber development from the regulatory divergence of transcription factor (TF) motifs. Finally, we constructed a reliable regulatory network of TFs related to ovule and fiber development based on chromatin accessibility and gene co-expression network. From this network, we discovered a novel TF, WRKY46, which may shape fiber development by regulating the lignin content. CONCLUSIONS: Our results not only reveal the contribution of TEs in fiber development, but also predict and validate the TFs related to fiber development, which will benefit the research of cotton fiber molecular breeding.

Fourier Transform Infrared (FT-IR) Spectroscopy and Simple Algorithm Analysis for Rapid and Non-Destructive Assessment of Cotton Fiber Maturity and Crystallinity for Plant Mapping.

Information on boll distribution within a cotton plant is critical to evaluate the adaptation and response of cotton plants to environmental and biotic stress in cotton production. Cotton researchers have applied available conventional fiber measurements, such as the high volume instrument (HVI) and advanced fiber information system (AFIS), to map the location and the timing of boll development and distribution within plants and further to determine within-plant variability of cotton fiber properties. Both HVI and AFIS require numerous cotton bolls combined for the measurement. As an alternative approach, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy was proposed to measure fiber maturity (MIR) and crystallinity (CIIR) of a sample as little as 0.5 mg lint. Extending fiber maturity and crystallinity measurement into a single boll for node-by-node mapping, FT-IR method might be advantageous due to less sampling amount compared with HVI and AFIS methods. Results showed that FT-IR technique enabled the evaluation of fiber MIR and CIIR at a boll level, which resulted in average MIR and CIIR values highly correlated with HVI micronaire (MIC) and AFIS maturity ratio (M). Hence, FT-IR technique possesses a good potential for a rapid and non-destructive node-by-node mapping of cotton boll maturity and crystallinity distribution.

Sphingolipid inhibitor response gene GhMYB86 controls fiber elongation by regulating microtubule arrangement.

Although the cell membrane and cytoskeleton play essential roles in cellular morphogenesis, the interaction between the membrane and cytoskeleton is poorly understood. Cotton fibers are extremely elongated single cells, which makes them an ideal model for studying cell development. Here, we used the sphingolipid biosynthesis inhibitor, fumonisin B1 (FB1), and found that it effectively suppressed the myeloblastosis (MYB) transcription factor GhMYB86, thereby negatively affecting fiber elongation. A direct target of GhMYB86 is GhTUB7, which encodes the tubulin protein, the major component of the microtubule cytoskeleton. Interestingly, both the overexpression of GhMYB86 and GhTUB7 caused an ectopic microtubule arrangement at the fiber tips, and then leading to shortened fibers. Moreover, we found that GhMBE2 interacted with GhMYB86 and that FB1 and reactive oxygen species induced its transport into the nucleus, thereby enhancing the promotion of GhTUB7 by GhMYB86. Overall, we established a GhMBE2-GhMYB86-GhTUB7 regulation module for fiber elongation and revealed that membrane sphingolipids affect fiber elongation by altering microtubule arrangement.

GhBZR3 suppresses cotton fiber elongation by inhibiting very-long-chain fatty acid biosynthesis.

The BRASSINAZOLE-RESISTANT (BZR) transcription factor is a core component of brassinosteroid (BR) signaling and is involved in the development of many plant species. BR is essential for the initiation and elongation of cotton fibers. However, the mechanism of BR-regulating fiber development and the function of BZR is poorly understood in Gossypium hirsutum L. (cotton). Here, we identified a BZR family transcription factor protein referred to as GhBZR3 in cotton. Overexpression of GhBZR3 in Arabidopsis caused shorter root hair length, hypocotyl length, and hypocotyl cell length, indicating that GhBZR3 negatively regulates cell elongation. Pathway enrichment analysis from VIGS-GhBZR3 cotton plants found that fatty acid metabolism and degradation might be the regulatory pathway that is primarily controlled by GhBZR3. Silencing GhBZR3 expression in cotton resulted in taller plant height as well as longer fibers. The very-long-chain fatty acid (VLCFA) content was also significantly increased in silenced GhBZR3 plants compared with the wild type. The GhKCS13 promoter, a key gene for VLCFA biosynthesis, contains two GhBZR3 binding sites. The results of yeast one-hybrid, electrophoretic mobility shift, and luciferase assays revealed that GhBZR3 directly interacted with the GhKCS13 promoter to suppress gene expression. Taken together, these results indicate that GhBZR3 negatively regulates cotton fiber development by reducing VLCFA biosynthesis. This study not only deepens our understanding of GhBZR3 function in cotton fiber development, but also highlights the potential of improving cotton fiber length and plant growth using GhBZR3 and its related genes in future cotton breeding programs.

GhROP6 GTPase modulates auxin accumulation in cotton fibers by regulating cell-specific GhPIN3a localization.

PIN-FORMED- (PIN) mediated polar auxin transport plays a predominant role in most auxin-triggered organogenesis in plants. Global control of PIN polarity at the plasma membrane contributes to the essential establishment of auxin maxima in most multicellular tissues. However, establishment of auxin maxima in single cells is poorly understood. Cotton fibers, derived from ovule epidermal cells by auxin-triggered cell protrusion, provide an ideal model to explore the underlying mechanism. Here, we report that cell-specific degradation of GhPIN3a, which guides the establishment of the auxin gradient in cotton ovule epidermal cells, is associated with the preferential expression of GhROP6 GTPase in fiber cells. In turn, GhROP6 reduces GhPIN3a abundance at the plasma membrane and facilitates intracellular proteolysis of GhPIN3a. Overexpression and activation of GhROP6 promote cell elongation, resulting in a substantial improvement in cotton fiber length.

Exploring the genetic diversity and population structure of upland cotton germplasm by iPBS-retrotransposons markers.

BACKGROUND: Upland cotton is one of the utmost significant strategic fiber crops, and play a vital role in the global textile industry. METHODS AND RESULTS: A total of 128 genotypes comprised Gossypium hirsutum L, Gossypium barbadense L., and pure lines were used to examine genetic diversity using iPBS-retrotransposon markers system. Eleven highly polymorphic primers yielded 287 bands and 99.65% polymorphism was recorded. The mean polymorphism information content was estimated at 0.297 and the average diversity indices for the effective number of alleles, Shannon's information index, and overall gene diversity were 1.481, 0.443, and 0.265, respectively. The analysis of molecular variance (AMOVA) revealed that 69% of the genetic variation was within the population. A model-based STRUCTURE algorithm divided the entire germplasm into four populations and one un-classified population, the genotypes G42 (originating in Egypt) and G128 (originating in the United States), showed the highest genetic distance (0.996) so these genotypes could be suggested for breeding programs as parental lines. CONCLUSIONS: This is the first investigation using an iPBS-retrotransposon marker system to examine the genetic diversity and population structure of upland cotton germplasm. The rich diversity found in upland cotton germplasm could be exploited as a genetic resource when developing breeding programs and could also help with efforts to breed cotton around the world. These findings also show the applicability and effectiveness of iPBS-retrotransposons for the molecular characterization of cotton germplasm.

Transforming municipal cotton waste into a multilayer fibre biocomposite with high strength.

We analyzed the problematic textile fiber waste as potential precursor material to produce multilayer cotton fiber biocomposite. The properties of the products were better than the current dry bearing type particleboards and ordinary dry medium-density fiberboard in terms of the static bending strength (67.86 MPa), internal bonding strength (1.52 MPa) and water expansion rate (9.57%). The three-layer, four-layer and five-layer waste cotton fiber composite (WCFC) were tried in the experiment, the mechanical properties of the three-layer WCFC are insufficient, the five-layer WCFC is too thick and the four-layer WCFC had the best comprehensive performance. The cross-section morphology of the four-layer WCFC shows a dense structure with a high number of adhesives attached to the fiber. The hardness and stiffness of the four-layer cotton fiber composite enhanced by the high crystallinity of cellulose content, and several chemical bondings were presence in the composites. Minimum mass loss (30%) and thermal weight loss rate (0.70%/°C) was found for the four-layer WCFC. Overall, our findings suggested that the use of waste cotton fiber (WCF) to prepare biocomposite with desirable physical and chemical properties is feasible, and which can potentially be used as building material, furniture and automotive applications.

A nitrocellulose/cotton fiber hybrid composite membrane for paper-based biosensor.

Nitrocellulose (NC) membrane was fabricated and tested for its potential use in various paper-based biosensors for use in point-of-care testing. However, contemporary technologies are complex, expensive, non-scalable, limited by conditions, and beset with potentially adverse effects on the environment. Herein, we proposed a simple, cost-effective, scalable technology to prepare nitrocellulose/cotton fiber (NC/CF) composite membranes. The NC/CF composite membranes with a diameter of 20 cm were fabricated in 15 min using papermaking technology, which contributes to scalability in the large-scale production of these composites. Compared with existing commercial NC membranes, the NC/CF composite membrane is characterized by small pore size (3.59 ± 0.19 µm), low flow rate (156 ± 55 s/40 mm), high dry strength (up to 4.04 MPa), and wet strength (up to 0.13 MPa), adjustable hydrophilic-hydrophobic (contact angles ranged from 29 ± 4.6 to 82.8 ± 2.4°), the good adsorption capacity of protein (up to 91.92 ± 0.07 µg). After lateral flow assays (LFAs) detection, the limit of detection is 1 nM, which is similar to commercial NC membrane (Sartorius CN 140). We envision the NC/CF composite membrane as a promising material for paper-based biosensors of point-of-care testing applications.

Transcriptome and Metabolome Profiling Unveil Pigment Formation Variations in Brown Cotton Lines (Gossypium hirsutum L.).

Naturally brown colored cotton (NBCC) is becoming increasingly popular due to its natural properties of coloration. However, poor fiber quality and color fading are key issues that are hindering the cultivation of naturally colored cotton. In this study, based on transcriptome and metabolome of 18 days post-anthesis (DPA), we compared the variations of pigment formation in two brown cotton fibers (DCF and LCF), with white cotton fiber (WCF) belonging to a near-isogenic line. A transcriptome study revealed a total of 15,785 differentially expressed genes significantly enriched in the flavonoid biosynthesis pathway. Furthermore, for flavonoid biosynthesis-related genes, such as flavonoid 3'5'-hydroxylase (F3'5'H), anthocyanidin synthase (ANS), anthocyanidin reductase (ANR), chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), and chalcone isomerase (CHI), their expressions significantly increased in LCF compared with DCF and WCF. Moreover, transcription factors MYB and bHLH were significantly expressed in LCF and DCF. Most flavonoid-related metabolites (myricetin naringenin, catechin, epicatechin-epiafzelechin, and epigallocatechin) were found to be more highly up-regulated in LCF and DCF than WCF. These findings reveal the regulatory mechanism controlling different brown pigmentation in cotton fibers and elucidate the need for the proper selection of high-quality brown cotton fiber breeding lines for promising fiber quality and durable brown color pigmentation.

Interpretation of convolutional neural networks reveals crucial sequence features involving in transcription during fiber development.

BACKGROUND: Upland cotton provides the most natural fiber in the world. During fiber development, the quality and yield of fiber were influenced by gene transcription. Revealing sequence features related to transcription has a profound impact on cotton molecular breeding. We applied convolutional neural networks to predict gene expression status based on the sequences of gene transcription start regions. After that, a gradient-based interpretation and an N-adjusted kernel transformation were implemented to extract sequence features contributing to transcription. RESULTS: Our models had approximate 80% accuracies, and the area under the receiver operating characteristic curve reached over 0.85. Gradient-based interpretation revealed 5' untranslated region contributed to gene transcription. Furthermore, 6 DOF binding motifs and 4 transcription activator binding motifs were obtained by N-adjusted kernel-motif transformation from models in three developmental stages. Apart from 10 general motifs, 3 DOF5.1 genes were also detected. In silico analysis about these motifs' binding proteins implied their potential functions in fiber formation. Besides, we also found some novel motifs in plants as important sequence features for transcription. CONCLUSIONS: In conclusion, the N-adjusted kernel transformation method could interpret convolutional neural networks and reveal important sequence features related to transcription during fiber development. Potential functions of motifs interpreted from convolutional neural networks could be validated by further wet-lab experiments and applied in cotton molecular breeding.

Data mining of transcriptional biomarkers at different cotton fiber developmental stages.

Advancement of the gene expression study provides comprehensive information on pivotal genes at different cotton fiber development stages. For the betterment of cotton fiber yield and their quality, genetic improvement is a major target point for the cotton community. Therefore, various studies were carried out to understand the transcriptional machinery of fiber leading to the detailed integrative as well as innovative study. Through data mining and statistical approaches, we identified and validated the transcriptional biomarkers for staged specific differentiation of fiber. With the unique mapping read matrix of ~ 200 cotton transcriptome data and sequential statistical analysis, we identified several important genes that have a deciding and specific role in fiber cell commitment, initiation and elongation, or secondary cell wall synthesis stage. Based on the importance score and validation analysis, IQ domain 26, Aquaporin, Gibberellin regulated protein, methionine gamma lyase, alpha/beta hydrolases, and HAD-like superfamily have shown the specific and determining role for fiber developmental stages. These genes are represented as transcriptional biomarkers that provide a base for molecular characterization for cotton fiber development which will ultimately determine the high yield.

Dynamic roles and intricate mechanisms of ethylene in epidermal hair development in Arabidopsis and cotton.

Ethylene affects many aspects of plant growth and development, including root hairs and trichomes growth in Arabidopsis, as well as fiber development in cotton, though the underlying mechanism is unclear. In this article, we update the research progress associated with the main genes in ethylene biosynthesis and signaling pathway, and we propose a clear ethylene pathway based on genome-wide identification of homologues in cotton. Expression pattern analysis using transcriptome data revealed that some candidate genes may contribute to cotton fiber development through the ethylene pathway. Moreover, we systematically summarized the effects of ethylene on the development of epidermal hair and the underlying regulatory mechanisms in Arabidopsis. Based on the knowledge of ethylene-promoted cell differentiation, elongation, and development in different tissues or plants, we advised a possible regulatory network for cotton fiber development with ethylene as the hub. Importantly, we emphasized the roles of ethylene as an important node in regulating cotton vegetative growth, and stress resistance, and suggested utilizing multiple methods to subtly modify ethylene synthesis or signaling in a tissue or spatiotemporal-specific manner to clarify its exact effect on architecture, adaptability of the plant, and fiber development, paving the way for basic research and genetic improvement of the cotton crop.

Microtubules play a crucial role in regulating actin organization and cell initiation in cotton fibers.

KEY MESSAGE: Dynamic organization of actin and microtubule cytoskeletons directs a distinct expansion behavior of cotton fiber initiation from cell elongation. Cotton fibers are highly elongated single cells derived from the ovule epidermis. Although actin and microtubule (MT) cytoskeletons have been implicated in cell elongation and secondary wall deposition, their roles in fiber initiation is poorly understood. Here, we used fluorescent probes and pharmacological approaches to study the roles of these cytoskeletal components during cotton fiber initiation. Both cytoskeletons align along the growth axis in initiating fibers. The dorsal view of ovules shows that unlike the fine actin filaments (AFs) in nonfiber cells, the AFs in fiber cells are dense and bundled. MTs are randomized in fiber cells and well-ordered in nonfiber cells. The pharmacological experiments revealed that the depolymerization of AFs and MTs assisted fiber initiation. Both AF stabilization and depolymerization inhibited fiber elongation. In contrast, the proper depolymerization of MTs promoted cell elongation, although the MT-stabilizing drug consistently resulted in a negative effect. Notably, we found that the organization of AFs was correlated with MT dynamics. Stabilizing the MTs by taxol treatment promoted the formation of AF bundles (in fiber initials) and transversely aligned AFs (in elongating fibers), whereas depolymerizing the MTs by oryzalin treatment promoted the fragmentation of AFs. Collectively, our data indicates that MTs plays a crucial role in regulating AF organization and early development of cotton fibers.

Comparison of paper-based nucleic acid extraction materials for point-of-care testing applications.

Cheap, rapid, simple and equipment-free nucleic acid extraction (NAE) is highly preferred for implementing nucleic acid detection at point-of-care (POC). Paper-based NAE materials have been extensively utilized due to their low cost, abundance, portability, biocompatibility and ease of chemical modification. However, it is challenging for users to choose the proper one from existing paper-based NAE materials for specific POC applications, which is determined by their physical and chemical properties. Additionally, building the relationship between the physical and chemical properties and the NAE efficiency of paper-based materials is instructive for development of new paper-based NAE materials. In this study, we first systematically compared the physical and chemical properties of six widely used paper-based NAE materials (namely Whatman filter paper #1, FTA card, FTA elute card, Fusion 5, silica membrane and polyethersulfone (PES) membrane), and then evaluated their NAE efficiency. The obtained results indicated that pore uniformity, wet strength, porosity and functional groups are key parameters to affect the efficiency of NAE. The NAE performance of FTA card is the best with high concentration and purity. Finally, we envision that more cost-effective paper-based NAE materials will be developed for POCT application in the future. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10570-022-04444-6.

An Unexpected Regulatory Sequence from Rho-Related GTPase6 Confers Fiber-Specific Expression in Upland Cotton.

Cotton fibers, single seed trichomes derived from ovule epidermal cells, are the major source of global textile fibers. Fiber-specific promoters are desirable to study gene function and to modify fiber properties during fiber development. Here, we revealed that Rho-related GTPase6 (GhROP6) was expressed preferentially in developing fibers. A 1240 bp regulatory region of GhROP6, which contains a short upstream regulatory sequence, the first exon, and the partial first intron, was unexpectedly isolated and introduced into transgenic cotton for analyzing promoter activity. The promoter of GhROP6 (proChROP6) conferred a specific expression in ovule surface, but not in the other floral organs and vegetative tissues. Reverse transcription PCR analysis indicated that proGhROP6 directed full-length transcription of the fused ß-glucuronidase (GUS) gene. Further investigation of GUS staining showed that proChROP6 regulated gene expression in fibers and ovule epidermis from fiber initiation to cell elongation stages. The preferential activity was enriched in fiber cells after anthesis and reached to peak on flowering days. By comparison, proGhROP6 was a mild promoter with approximately one-twenty-fifth of the strength of the constitutive promoter CaMV35S. The promoter responded to high-dosage treatments of auxin, gibberellin and salicylic acid and slightly reduced GUS activity under the in vitro treatment. Collectively, our data suggest that the GhROP6 promoter has excellent activity in initiating fibers and has potential for bioengineering of cotton fibers.

Effect of Microwave Plasma Pre-Treatment on Cotton Cellulose Dissolution.

The utilization of cellulose to its full potential is constrained by its recalcitrance to dissolution resulting from the rigidity of polymeric chains, high crystallinity, high molecular weight, and extensive intra- and intermolecular hydrogen bonding network. Therefore, pretreatment of cellulose is usually considered as a step that can help facilitate its dissolution. We investigated the use of microwave oxygen plasma as a pre-treatment strategy to enhance the dissolution of cotton fibers in aqueous NaOH/Urea solution, which is considered to be a greener solvent system compared to others. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and Powder X-ray Diffraction analyses revealed that plasma pretreatment of cotton cellulose leads to physicochemical changes of cotton fibers. Pretreatment of cotton cellulose with oxygen plasma for 20 and 40 min resulted in the reduction of the molecular weight of cellulose by 36% and 60% and crystallinity by 16% and 25%, respectively. This reduction in molecular weight and crystallinity led to a 34% and 68% increase in the dissolution of 1% (w/v) cotton cellulose in NaOH/Urea solvent system. Thus, treating cotton cellulose with microwave oxygen plasma alters its physicochemical properties and enhanced its dissolution.

GhGASA10-1 promotes the cell elongation in fiber development through the phytohormones IAA-induced.

BACKGROUND: Cotton is an important cash crop. The fiber length has always been a hot spot, but multi-factor control of fiber quality makes it complex to understand its genetic basis. Previous reports suggested that OsGASR9 promotes germination, width, and thickness by GAs in rice, while the overexpression of AtGASA10 leads to reduced silique length, which is likely to reduce cell wall expansion. Therefore, this study aimed to explore the function of GhGASA10 in cotton fibers development. RESULTS: To explore the molecular mechanisms underlying fiber elongation regulation concerning GhGASA10-1, we revealed an evolutionary basis, gene structure, and expression. Our results emphasized the conservative nature of GASA family with its origin in lower fern plants S. moellendorffii. GhGASA10-1 was localized in the cell membrane, which may synthesize and transport secreted proteins to the cell wall. Besides, GhGASA10-1 promoted seedling germination and root extension in transgenic Arabidopsis, indicating that GhGASA10-1 promotes cell elongation. Interestingly, GhGASA10-1 was upregulated by IAA at fiber elongation stages. CONCLUSION: We propose that GhGASA10-1 may promote fiber elongation by regulating the synthesis of cellulose induced by IAA, to lay the foundation for future research on the regulation networks of GASA10-1 in cotton fiber development.

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.

Global expression dynamics and miRNA evolution profile govern floral/fiber architecture in the modern cotton (Gossypium).

MAIN CONCLUSION: Majority of differentially expressed miRNAs with functional attributes have been recruited independently and parallelly during allopolyploidy followed by the millennia of human selection of both domesticated G. hirsutum and G. barbadense. The genus Gossypium is a marvelous evolutionary model for studying allopolyploidy and morpho-evolution of long-spinnable fibers from the ancestral wild-fuzz. Many genes, transcription factors, and notably, the regulatory miRNAs essentially govern such remarkable modern fiber phenotypes. To comprehend the impact of allopolyploidy on the evolutionary selection of transcriptional dynamicity of key miRNAs, comparative transcriptome profiling of vegetative and fiber tissues of domesticated diploid G. arboreum (A2) and allopolyploid cotton species G. hirsutum (AD1), and G. barbadense (AD2) identified > 300 differentially expressed miRNAs (DEmiRs) within or between corresponding tissues of A2, AD1 and AD2 species. Up to 49% and 32% DEmiRs were up- and down-regulated at fiber initiation stage of AD1 and AD2 species, respectively, whereas 50% and 18% DEmiRs were up- and down-regulated at fiber elongation stage of both the allopolyploid species. Interestingly, A-subgenome-specific DEmiRs exhibit expression dominance in the allopolyploid genetic backgrounds. Comparative spatio-temporal expression analyses of AD1 and AD2 species discovered that a majority of DEmiRs were recruited independently under millennia of human selection during domestication. Functional annotations of these DEmiRs revealed selection of associated molecular functions such as hormone-signaling, calcium-signaling and reactive oxygen species (ROS) signaling during fiber initiation and elongation. To validate the functional attributes of annotated DEmiRs, we demonstrated for the first time that the target-mimicry-based constitutive diminution of auxin-signaling associated miR167 directly affected the differentiation of floral and fiber tissues of transgenic cotton. These results strongly suggested that the evolutionarily favored DEmiRs including miR167 were involved in the transcriptional regulation of numerous genes during cotton evolution for enhanced fiber-associated agronomic traits.