Fiber Elongation Research Articles

Novel Dry Spinning Process of Natural Macromolecules for Sustainable Fiber Material -1- Proof of the Concept Using Silk Fibroin.

Researchers around the world are developing technologies to minimize carbon dioxide emissions or carbon neutrality in various fields. In this study, the dry spinning of regenerated silk fibroin (RSF) was achieved as a proof of concept for a process using ionic liquids as dissolution aids and plasticizers in developing natural polymeric materials. A dry spinning equipment system combining a stainless-steel syringe and a brushless motor was built to generate fiber compacts from a dope of silk fibroin obtained by degumming silkworm silk cocoons and ionic liquid 1-hexyl-3-methyl-imidazolium chloride ([HMIM][Cl]) according to a general method. The maximum stress and maximum elongation of the RSF fibers were 159.9 MPa and 31.5%, respectively. RSF fibers containing ionic liquids have a homogeneous internal structure according to morphological investigations. Elemental analysis of fiber cross sections revealed the homogeneous distribution of nonvolatile ionic liquid [HMIM][Cl] in RSF fibers. Furthermore, the removal of ionic liquids from RSF fibers through impregnation washing with organic solvents was verified to enhance industrial applications. Tensile testing showed that the fiber strength could be maintained even after removing the ionic liquid. Thermogravimetric analysis results show that the organic solvent 1,1,1,3,3,3-hexafluoro-2-propanol is chemically coordinated to silk fibroin and, as a natural polymer, can withstand heat up to 250 °C.

Fiber-specific overexpression of GhACO1 driven by E6 promoter improves cotton fiber quality and yield

Cotton (Gossypium hirsutum) is the most important fiber crop globally and there is an incentive to improve cotton fiber yield and quality to meet the growing market demand. 1-Aminocyclopropane-1-Carboxylic Acid Oxidase (ACO) has been identified as a rate-limiting enzyme in the biosynthesis of ethylene that is known to play a pivotal regulatory role in fiber development. According to transcriptomic data analysis, GhACO1 is preferentially expressed at fiber elongation stage in a number of G. hirsutum varieties, suggestive of its involvement in regulating fiber development. Ethylene is known to cause premature senescence, and to abrogate its potential negative effects on plant growth by constitutive overexpression of GhACO1, a fiber-specific promoter E6 that imparts strong transcriptional activity in fiber elongation stage was employed to drive GhACO1 expression to improve fiber quality. The E6::GhACO1 cotton transgenic lines showed substantial improvements in fiber length, fiber strength and fiber yield relative to wild type. Exogenous application of pyrazinecarboxylic acid that is an effective inhibitor of ACO enzyme inhibited fiber elongation in ovule culture, validating that GhACOs may improve fiber quality by increasing ethylene levels. Furthermore, RNA-Seq analysis showed that upregulation of GhACO1 can activate the transcription of genes that are involved in hydrogen peroxide metabolism, cell wall loosening and cytoskeleton arrangement, thereby promoting fiber elongation. These findings suggest that GhACO1 is a key regulator of fiber development, and the application of “E6::GhACO1” strategy breaks the negative correlation between fiber quality and fiber yield, providing a novel route in formulating fiber improvement strategies in cotton.

Chemical analysis of amyloid β aggregation inhibitors derived from Geranium thunbergii

Amyloid β (Aβ) aggregates in the brains of patients with Alzheimer's disease (AD) and accumulates via oligomerization and subsequent fiber elongation processes. These toxicity-induced neuronal damage and shedding processes advance AD progression. Therefore, Aβ aggregation-inhibiting substances may contribute to the prevention and treatment of AD. We screened for Aβ42 aggregation inhibitory activity using various plant extracts and compounds, and found high activity for a Geranium thunbergii extract (EC50 = 18 μg/mL). Therefore, we screened for Aβ42 aggregation inhibitors among components of a G. thunbergii extract and investigated their chemical properties in this study. An active substance was isolated from the ethanol extract of G. thunbergii based on the Aβ42 aggregation inhibitory activity as an index, and the compound was identified as geraniin (1) based on spectral data. However, although geraniin showed in vitro aggregation-inhibition activity, no binding to Aβ42 was observed via saturation transfer difference-nuclear magnetic resonance (STD-NMR). In contrast, the hydrolysates gallic acid (2) and corilagin (5) showed aggregation-inhibiting activity and binding was observed via STD-NMR. Therefore, the hydrolysates produced under the conditions of the activity test may contribute to the Aβ42 aggregation-inhibition activity of G. thunbergii extracts. Geraniin derivatives may help prevent and treat AD.

Effect of Surface Modification of Himalayan Nettle Fiber and Characterization of the Morphology, Physical and Mechanical Properties

Abstract The process of retting bast fiber plants for the production of long fiber has presented major challenges. Water retting, dew retting, chemical extraction, and micro-organism (fungi, enzymes) techniques were applied to the extraction of natural fibers. The two nettle samples were extracted with water retting for 14 days and dew retting for 4 weeks. This research investigated the effects on the traditional retting process of nettle fiber by fungi and bacteria formation in lignocellulosic. The latter biological extraction methods successfully degraded the lignin and pectin materials of the fiber and increases the cellulose content. These extraction methods produced high quality fiber and tensile strength at a low cost. This study determined the chemical, physical, and mechanical characteristics such as fiber cellulose, non-cellulosic content, tensile strength, tenacity, and elongation break to see how treatments affected them. The treated fiber surface morphology was characterized using scanning electron microscopy. To evaluate functional group alterations, Fourier-transform infrared spectroscopy was used on the fiber specimen.

Revealing Genetic Differences in Fiber Elongation between the Offspring of Sea Island Cotton and Upland Cotton Backcross Populations Based on Transcriptome and Weighted Gene Coexpression Networks.

Fiber length is an important indicator of cotton fiber quality, and the time and rate of cotton fiber cell elongation are key factors in determining the fiber length of mature cotton. To gain insight into the differences in fiber elongation mechanisms in the offspring of backcross populations of Sea Island cotton Xinhai 16 and land cotton Line 9, we selected two groups with significant differences in fiber length (long-fiber group L and short-fiber group S) at different fiber development stages 0, 5, 10 and 15 days post-anthesis (DPA) for transcriptome comparison. A total of 171.74 Gb of clean data was obtained by RNA-seq, and eight genes were randomly selected for qPCR validation. Data analysis identified 6055 differentially expressed genes (DEGs) between two groups of fibers, L and S, in four developmental periods, and gene ontology (GO) term analysis revealed that these DEGs were associated mainly with microtubule driving, reactive oxygen species, plant cell wall biosynthesis, and glycosyl compound hydrolase activity. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that plant hormone signaling, mitogen-activated protein kinase (MAPK) signaling, and starch and sucrose metabolism pathways were associated with fiber elongation. Subsequently, a sustained upregulation expression pattern, profile 19, was identified and analyzed using short time-series expression miner (STEM). An analysis of the weighted gene coexpression network module uncovered 21 genes closely related to fiber development, mainly involved in functions such as cell wall relaxation, microtubule formation, and cytoskeletal structure of the cell wall. This study helps to enhance the understanding of the Sea Island–Upland backcross population and identifies key genes for cotton fiber development, and these findings will provide a basis for future research on the molecular mechanisms of fiber length formation in cotton populations.

Effect of Okra Plant Lifespan upon Tensile Properties of Okra Fibers

ABSTRACT This study has been carried out to identify the effect of the okra plant lifespan upon the tensile properties, that is, fiber bundle strength and elongation of the yielded fibers. 90 ± 10 days, 120 ± 10 days, and 160 ± 10 days matured crop waste were subjected to different retting conditions (retting duration and retting medium flow rate). Water was used as retting medium with two different flow rates (0 and 6.5 m/min). Five retting durations were taken for this study between 11 and 35 days. The bundle tenacity (gf/tex) and elongation at break (%) were measured by Instron automatic bundle strength tester for the extracted okra fibers. The study revealed that okra fiber extracted through the running water showed better tensile strength (at least 14% higher, range 14–80%) than fiber extracted through stagnant water retting conditions at every retting duration (11–35 days) for the different lifespans of okra plants. Okra fiber bundle tenacity continuously reduced with the retting period ranging from 11 to 35 days irrespective of okra plant lifespan and retting conditions. Improvement in tenacity was found from 90 ± 10 days to 120 ± 10 days okra plant lifespan, but no significant improvement was found after 120 ± 10 days okra plant lifespan. No significant effect of elongation at break (%) was found for the okra plant lifespan and retting conditions.

The hexokinase Gene Family in Cotton: Genome-Wide Characterization and Bioinformatics Analysis.

Hexokinase (HXK) is involved in hexose phosphorylation, sugar sensing, and signal transduction, all of which regulate plant growth and adaptation to stresses. Gossypium hirsutum L. is one of the most important fiber crops in the world, however, little is known about the HXKs gene family in G. hirsutum L. We identified 17 GhHXKs from the allotetraploid G. hirsutum L. genome (AADD). G. raimondii (DD) and G. arboreum (AA) are the diploid progenitors of G. hirsutum L. and contributed equally to the At_genome and Dt_genome GhHXKs genes. The chromosomal locations and exon-intron structures of GhHXK genes among cotton species are conservative. Phylogenetic analysis grouped the HXK proteins into four and three groups based on whether they were monocotyledons and dicotyledons, respectively. Duplication event analysis demonstrated that HXKs in G. hirsutum L. primarily originated from segmental duplication, which prior to diploid hybridization. Experiments of qRT-PCR, transcriptome and promoter cis-elements demonstrated that GhHXKs’ promoters have auxin and GA responsive elements that are highly expressed in the fiber initiation and elongation stages, while the promoters contain ABA-, MeJA-, and SA-responsive elements that are highly expressed during the synthesis of the secondary cell wall. We performed a comprehensive analysis of the GhHXK gene family is a vital fiber crop, which lays the foundation for future studies assessing its role in fiber development.

Systematic analysis and comparison of CaLB genes reveal the functions of GhCaLB42 and GhCaLB123 in fiber development and abiotic stress in cotton

Ca2+-dependent lipid-binding (CaLB) family proteins, containing C2 domain, play an important role in plant growth, development, and abiotic stress response. There has been no systematic identification of CaLB family genes in cotton (Gossypium). In this study, 196 GhCaLBs were identified and divided into five groups by phylogenetic tree analysis in Gossypium hirsutum. Gene structure and conserved protein motif analysis supported the evolutionary conservation of GhCaLBs. Whole-genome or segmental duplications contributed to the expansion of GhCaLBs. 2144 orthologous and paralogous CaLB gene pairs among four cotton species were detected. And Ka/Ks values analysis showed that CaLBs experienced strong purification selection. Numerous hormone-regulated, stress-responsive, and growth and development cis-elements were detected in the 2 kb promoter regions of GhCaLBs. Besides, transcriptome data combined with qRT-PCR analysis showed some GhCaLBs were preferentially expressed in ovule or fiber. Subcellular localization experiment revealed that GhCaLB42-GFP was located in nucleus and cell membrane, while GhCalB123-GFP was in cell membrane. Overexpressing GhCaLB42 significantly promoted the elongation and density of leaf trichomes in transgenic Arabidopsis, while GhCaLB123 overexpression inhibited the elongation of leaf trichomes. Histochemical staining experiments showed that GhCaLB123 overexpression lines could significantly increase the thickness of xylem vessels and interfascicular fibers cell wall of stem compared with WT. GhCaLB42 may positively regulate fiber elongation, and GhCaLB123 inhibited elongation but promoted secondary cell wall (SCW) thickening in fiber. Yeast two-hybrid assays indicated that GhCaLB42 protein had multiple biological functions including fiber development and abiotic stress response, and GhCaLB123 might participate in substance transport for the cellulose synthesis. GhCaLB42 and its two interaction genes GhTHi1–1 and GhCIPK9 were induced to be highly expressed under ABA treatment. These findings provide an important foundation for understanding the functions of specific cotton CaLB genes and for the effective selection of fiber development related genes.

The GhMAX2 gene regulates plant growth and fiber development in cotton

Strigolactones (SLs) are a new type of plant endogenous hormones that have been found to regulate plant growth and architecture. At present, some genes related to the biosynthesis and signaling pathway of SLs have been isolated in plants such as Arabidopsis thaliana, Pisum sativum and Oryza sativa. However, the signaling pathway and specific mechanism of SLs in cotton remain unclear. In this study, we identified the SLs signaling gene GhMAX2 and demonstrated its function in plant growth and architecture in Gossypium hirsutum. Bioinformatics analysis showed that GhMAX2 mainly consists of an α-helix and a random coil and includes a large number of leucine-rich repeats. GhMAX2 was highly expressed in root, stem, flower, and fibers at 20 days post-anthesis (DPA). GhMAX2 promoter-driven β-glucuronidase expression was present exclusively in the root, main inflorescence, flower, and silique. Subcellular localization showed that GhMAX2 is targeted to the nucleus. Heterologously expressed GhMAX2 can rescue the phenotype of Arabidopsis max2-1 mutant, indicating that the function of MAX2 is highly conserved between G. hirsutum and A. thaliana species. In addition, the knockdown expression of GhMAX2 in cotton resulted in significantly reduced plant height, slow growth, short internodes, and reduced fiber length. These findings indicate that GhMAX2 probably contributes to plant growth, architecture and fiber elongation in cotton. The study reveals insights into the roles of GhMAX2-mediated SL/KAR signaling in cotton and provides a valuable foundation for the cultivation of cotton plants in the future.

Molecular Regulation of Cotton Fiber Development: A Review.

Cotton (Gossypium spp.) is an economically important natural fiber crop. The quality of cotton fiber has a substantial effect on the quality of cotton textiles. The identification of cotton fiber development-related genes and exploration of their biological functions will not only enhance our understanding of the elongation and developmental mechanisms of cotton fibers but also provide insights that could aid the cultivation of new cotton varieties with improved fiber quality. Cotton fibers are single cells that have been differentiated from the ovule epidermis and serve as a model system for research on single-cell differentiation, growth, and fiber production. Genes and fiber formation mechanisms are examined in this review to shed new light on how important phytohormones, transcription factors, proteins, and genes linked to fiber development work together. Plant hormones, which occur in low quantities, play a critically important role in regulating cotton fiber development. Here, we review recent research that has greatly contributed to our understanding of the roles of different phytohormones in fiber development and regulation. We discuss the mechanisms by which phytohormones regulate the initiation and elongation of fiber cells in cotton, as well as the identification of genes involved in hormone biosynthetic and signaling pathways that regulate the initiation, elongation, and development of cotton fibers.

Identification of Candidate Genes for Lint Percentage and Fiber Quality Through QTL Mapping and Transcriptome Analysis in an Allotetraploid Interspecific Cotton CSSLs Population.

Upland cotton (Gossypium hirsutum) has long been an important fiber crop, but the narrow genetic diversity of modern G. hirsutum limits the potential for simultaneous improvement of yield and fiber quality. It is an effective approach to broaden the genetic base of G. hirsutum through introgression of novel alleles from G. barbadense with excellent fiber quality. In the present study, an interspecific chromosome segment substitution lines (CSSLs) population was established using G. barbadense cultivar Pima S-7 as the donor parent and G. hirsutum cultivar CCRI35 as the recipient parent. A total of 105 quantitative trait loci (QTL), including 85 QTL for fiber quality and 20 QTL for lint percentage (LP), were identified based on phenotypic data collected from four environments. Among these QTL, 25 stable QTL were detected in two or more environments, including four for LP, eleven for fiber length (FL), three for fiber strength (FS), six for fiber micronaire (FM), and one for fiber elongation (FE). Eleven QTL clusters were observed on nine chromosomes, of which seven QTL clusters harbored stable QTL. Moreover, eleven major QTL for fiber quality were verified through analysis of introgressed segments of the eight superior lines with the best comprehensive phenotypes. A total of 586 putative candidate genes were identified for 25 stable QTL associated with lint percentage and fiber quality through transcriptome analysis. Furthermore, three candidate genes for FL, GH_A08G1681 (GhSCPL40), GH_A12G2328 (GhPBL19), and GH_D02G0370 (GhHSP22.7), and one candidate gene for FM, GH_D05G1346 (GhAPG), were identified through RNA-Seq and qRT-PCR analysis. These results lay the foundation for understanding the molecular regulatory mechanism of fiber development and provide valuable information for marker-assisted selection (MAS) in cotton breeding.

Arginine Decarboxylase Gene ADC2 Regulates Fiber Elongation in Cotton

Cotton is an important agro-industrial crop providing raw material for the textile industry. Fiber length is the key factor that directly affects fiber quality. ADC, arginine decarboxylase, is the key rate-limiting enzyme in the polyamine synthesis pathway; whereas, there is no experimental evidence that ADC is involved in fiber development in cotton yet. Our transcriptome analysis of the fiber initiation material of Gossypium arboreum L. showed that the expression profile of GaADC2 was induced significantly. Here, GhADC2, the allele of GaADC2 in tetraploid upland cotton Gossypium hirsutum L., exhibited up-regulated expression pattern during fiber elongation in cotton. Levels of polyamine are correlated with fiber elongation; especially, the amount of putrescine regulated by ADC was increased. Scanning electron microscopy showed that the fiber length was increased with exogenous addition of an ADC substrate or product putrescine; whereas, the fiber density was decreased with exogenous addition of an ADC specific inhibitor. Next, genome-wide transcriptome profiling of fiber elongation with exogenous putrescine addition was performed to determine the molecular basis in Gossypium hirsutum. A total of 3163 differentially expressed genes were detected, which mainly participated in phenylpropanoid biosynthesis, fatty acid elongation, and sesquiterpenoid and triterpenoid biosynthesis pathways. Genes encoding transcription factors MYB109, WRKY1, and TCP14 were enriched. Therefore, these results suggested the ADC2 and putrescine involvement in the development and fiber elongation of G. hirsutum, and provides a basis for cotton fiber development research in future.

Mechanical Properties Evolution and Damage Mechanism of Kevlar Fiber under Ozone Exposure in Near-Space Simulation

The stratospheric airship, a long-term floating vehicle in near-space, has become a new hotspot in aerospace exploration. The airship’s envelope material is vulnerable to ozone exposure in near-space and degrades. This paper used typical Kevlar fiber as the research material for an ozone exposure experiment in a near-space simulated environment. The results showed that the elongation of the Kevlar fiber decreased and the elastic modulus increased after ozone exposure. The tensile strength of fiber decreased gradually with an increase in ozone concentration and exposure time. When ozone concentration increased from 0 pphm to 1000 pphm, the tensile strength of fiber decreased from 2397 MPa to 2059 MPa. With increasing ozone exposure time from 0 h to 1000 h under ozone concentration 1000 pphm, the tensile strength of fiber decreased from 2332 MPa to 1954 MPa. The hydrogen bonds and partial amide groups in the fiber structure were damaged, and the surface chemical functional groups of the Kevlar fiber were reassembled under ozone exposure. Low molecular weight oxidation products, including -COO- structures, formed on the surface of the Kevlar fiber. This work explores the ground simulation method in a near-space environment and enriches the service data of airship envelope materials.

Failure properties of flexible composite under trouser-shaped tests

The failure properties of trouser-shaped tests on flexible composite called Uretek-3216LV were studied by experiment and theory. Based on the failure mechanical behavior of the trouser-type tests, theoretical model of the three stages (displacement, fiber stretching, and fiber breaking) were established. In the model, a spring system including the tail, tear del, and the fiber elongation is introduced to characterize the mechanical behavior of the displacement stage and the fiber stretching stages. Based on the strain wave model, the failure model of fiber breaking stage is established. Based on the trouser tearing tests and failure model, the trouser-shaped failure performance of flexible composites was analyzed in detail.

Inheritance, QTLs, and Candidate Genes of Lint Percentage in Upland Cotton.

Cotton (Gossypium spp.) is an important natural fiber plant. Lint percentage (LP) is one of the most important determinants of cotton yield and is a typical quantitative trait with high variation and heritability. Many cotton LP genetic linkages and association maps have been reported. This work summarizes the inheritance, quantitative trait loci (QTLs), and candidate genes of LP to facilitate LP genetic study and molecular breeding. More than 1439 QTLs controlling LP have been reported. Excluding replicate QTLs, 417 unique QTLs have been identified on 26 chromosomes, including 243 QTLs identified at LOD >3. More than 60 are stable, major effective QTLs that can be used in marker-assisted selection (MAS). More than 90 candidate genes for LP have been reported. These genes encode MYB, HOX, NET, and other proteins, and most are preferentially expressed during fiber initiation and elongation. A putative molecular regulatory model of LP was constructed and provides the foundation for the genetic study and molecular breeding of LP.

Probabilistic Model of the Kinematics of the Device for Reducing Elongation of Flax Fiber Stems in the Tape

Introduction. The main reason for the crisis state of flax growing is the losses of the flax fiber portions when it is extracted from the crop. This is due to excessive elongation of the stems in the layer. It was found that the most convenient way to reduce elongation in the field conditions when turning over flax strips by striking the butt portions in the direction of the stems. The authors propose to use for this purpose a pickup flax turner with a conveyor-type inclined flax butting machine. The purpose of the research is to increase the efficiency of flax tapes leveling process by butting flax stems. Materials and Methods. It is noted that the maximum effect will be provided by a counterimpact in the direction of the flax stems. For this purpose, the speed of motion of the butting surface relative to the retted straw transversely to the flax stems should have a constant zero value. The specified mode can be realized by a conveyor with roller activators. In the article, the random nature of the working conditions of machine units in the field was noted that is an additional obstacle for processing the flax tapes by the suggested method. Therefore, it is recommended to use probabilistic and graph-analytical methods of calculation when designing flax butting machines. Results. Using the graph-analytical method, a probabilistic model linking the kinematics of the proposed device with the probability of causing counter-strikes on the flax butts was obtained. It was found that two-roller activators in combination with inclination of butting surface will provide pronounced impacts, increase speed and probability of their application. Parameters and operating modes of inclined conveyor-type butting machine were substantiated experimentally. Discussion and Conclusion. Application of the proposed method, taking into account the results obtained, will reduce the elongation of flax stems in strips by 5.6% for one turning over and the yield of long fiber by 2.5–3.0%.

Assessment of Changes in Corn Husk Fibres after Acid Treatment

Sustainability is desirable in any activity, including farming. Adding value to agricultural wastes such as stover (waste from corn cultivation) would provide financial benefits to farmers while reducing the environmental load of disposal. The literature identifies stover as being a raw material for bio-ethanol and a reinforcement for composites. Fibre from corn husks is generally extracted using an alkali digestion method followed optionally by enzymatic degradation. In this study, acid treatment was investigated for its feasibility to improve the desirable characteristics of alkali extracted corn husk fibres. The results revealed that increasing the acid concentration decreased fibre properties such as average fibre length, linear density and elongation at break. However, breaking tenacity achieved a maximum value, on treatment with 7.5 g/l sulfuric acid, before decreasing. These properties indicate the treatment’s adequacy for use in textile products. Acid treatment did not significantly alter thermo-gravimetric analysis values, indicating that the fibre could withstand wet processing conditions.

Three root hair defective genes, GhRHD3-1, GhRHD4-1, and GhRSL4-1, regulate fiber cell elongation in cotton

Cotton fibers, single epidermal cells, are most prevalent natural product in textile industries. Root hairs, similar to cotton fibers, are also single cell trichomes. Root hair defective gene (RHD) has been found to greatly modulate root hair development. However, the function of RHD remains unexplored in cotton. We identified 19 RHDs in Gossypium hirsutum. GhRHD3–1, GhRHD4–1, and GhRSL4–1 were highly expressed in fiber elongation stage and promoter-driven GUS of these three genes were mainly expressed in root hair. GhRHD3–1, GhRHD4–1, and GhRSL4–1 localized to the endoplasmic reticulum, cytomembrane, and nucleus, respectively. Overexpression of these three genes each in Arabidopsis increased root length. Silencing these three genes each in cotton reduced plant height and fiber length. Gene Ontology (GO) analysis showed that cell wall, photosynthesis, and oxidoreductase activity related processes were enriched in down-regulated genes after silencing GhRHD3–1, GhRHD4–1, and GhRSL4–1, respectively. Transcripts of the genes identified from enriched terms were also reduced after silencing GhRHD3–1, GhRHD4–1, and GhRSL4–1. Our results suggest that GhRHD3–1, GhRHD4–1, and GhRSL4–1 promote fiber elongation through regulating cell wall, photosynthesis, and oxidoreductase activity pathways, respectively. This study deepens our understanding of the GhRHDs in cotton and will help us breed better cotton varieties in future.

The bHLH/HLH transcription factors GhFP2 and GhACE1 antagonistically regulate fiber elongation in cotton.

Basic helix-loop-helix/helix-loop-helix (bHLH/HLH)transcription factors play important roles in cell elongation in plants. However, little is known about how bHLH/HLH transcription factors antagonistically regulate fiber elongation in cotton (Gossypium hirsutum). In this study, we report that two bHLH/HLH transcription factors, fiber-related protein 2 (GhFP2) and ACTIVATOR FOR CELL ELONGATION 1 (GhACE1), function in fiber development of cotton. GhFP2 is an atypical bHLH protein without the basic region, and its expression is regulated by brassinosteroid (BR)-related BRASSINAZOLE RESISTANT 1 (GhBZR1). Overexpression of GhFP2 in cotton hindered fiber elongation, resulting in shortened fiber length. In contrast, suppression of GhFP2 expression in cotton promoted fiber development, leading to longer fibers compared with the wild-type. GhFP2 neither contains a DNA-binding domain nor has transcriptional activation activity. Furthermore, we identified GhACE1, a bHLH protein that interacts with GhFP2 and positively regulates fiber elongation. GhACE1 could bind to promoters of plasma membrane intrinsic protein 2;7 (GhPIP2;7) and expansions 8 (GhEXP8) for directly activating their expression, but the interaction between GhFP2 and GhACE1 suppressed transcriptional activation of these target genes by GhACE1. Taken together, our results indicate that GhACE1 promotes fiber elongation by activating expressions of GhPIP2;7 and GhEXP8, but its transcription activation on downstream genes may be obstructed by BR-modulated GhFP2. Thus, our data reveal a key mechanism for fiber cell elongation through a pair of antagonizing HLH/bHLH transcription factors in cotton.

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

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.