Fiber Cell Elongation Research Articles

Regulatory networks of coresident subgenomes during rapid fiber cell elongation in upland cotton

Cotton, an intriguing plant species shaped by polyploidization, evolution, and domestication, holds particular interest due to the complex mechanisms governing fiber traits across its two subgenomes. However, the regulatory elements or transcriptional networks between subgenomes during fiber elongation remain to be fully clarified. Here, we analyzed 1462 cotton fiber samples to reconstruct the gene-expression regulatory networks that influence fiber cell elongation. Inter-subgenome expression quantitative trait loci (eQTLs) largely dictate gene transcription, with a notable tendency for the D subgenome to regulate A-subgenome eGenes. This regulation reveals synchronized homoeologous gene expression driven by co-localized eQTLs and divergent patterns that diminish genetic correlations, thus leading to preferential expression in the A and D subgenomes. Hotspot456 emerged as a key regulator of fiber initiation and elongation, and artificial selection of trans-eQTLs in hotspot456 that positively regulate KCS1 has facilitated cell elongation. Experiments designed to clarify the roles of trans-eQTLs in improved fiber breeding confirmed the inhibition of GhTOL9 by a specific trans-eQTL via GhWRKY28, which negatively affects fiber elongation. We propose a model in which the GhWRKY28–GhTOL9 module regulates this process through the ESCRT (endosomal sorting complex required for transport) pathway. This research significantly advances our understanding of cotton’s evolutionary and domestication processes and the intricate regulatory mechanisms that underlie significant plant traits.

GhEXL3 participates in brassinosteroids regulation of fiber elongation in Gossypium hirsutum.

Cotton fiber (Gossypium hirsutum) serves as an ideal model for investigating the molecular mechanisms of plant cell elongation at the single-cell level. Brassinosteroids (BRs) play a crucial role in regulating plant growth and development. However, the mechanism by which BR influences cotton fiber elongation remains incompletely understood. In this study, we identified EXORDIUM-like (GhEXL3) through transcriptome analysis of fibers from BR-deficient cotton mutant pagoda 1 (pag1) and BRI1-EMS-SUPPRESSOR 1 (GhBES1.4, encoding a central transcription factor of BR signaling) overexpression cotton lines. Knockout of GhEXL3 using CRISPR/Cas9 was found to impede cotton fiber elongation, while its overexpression promoted fiber elongation, suggesting a positive regulatory function for GhEXL3 in fiber elongation. Furthermore, in vitro ovule culture experiments revealed that the overexpression of GhEXL3 partially counteracted the inhibitory effects of brassinazole (BRZ) on cotton fiber elongation, providing additional evidence of GhEXL3 involvement in BR signaling pathways. Moreover, our findings demonstrate that GhBES1.4 directly binds to the E-box (CACGTG) motif in the GhEXL3 promoter region and enhances its transcription. RNA-seq analysis revealed that overexpression of GhEXL3 upregulated the expression of EXPs, XTHs, and other genes associated with fiber cell elongation. Overall, our study contributes to understanding the mechanism by which BR regulates the elongation of cotton fibers through the direct modulation of GhEXL3 expression by GhBES1.4.

A brassinosteroid signal regulated beta-tubulin GhTUB17 play a role in cotton fiber elongation by influencing microtubule organization

Cotton (Gossypium hirsutum L.) is an important natural fiber crop in the world. Cotton fiber cell is an extremely elongated single cell and a major cash product of cotton plants. Both brassinosteroids (BRs) and cytoskeleton play essential roles in fiber cell elongation. However, the relationship of BRs with cytoskeleton in fiber elongation is largely unknown. In the study, a BRs responsive beta-tubulin gene GhTUB17 was identified, which preferentially expressed in fiber cell and peaked in the rapid elongation stage. GhTUB17 was up- and down-regulated by brassinolide (BL) and brassinozole (BRZ), respectively. Furthermore, compared with control, GhTUB17 expression was increased in transgenic fiber cell overexpressing GhBES1, a transcription factor in BRs signaling, while was decreased in the fiber of li-1, a short fiber mutant of upland cotton. GhBES1 could bind to the promoter of GhTUB17 and positively regulate its expression. Overexpressing GhTUB17 promoted fiber elongation while suppressing GhTUB17 inhibited fiber elongation. The arrangement patterns of both microtubule and microfilament were altered in transgenic cotton fibers. These results indicated that GhTUB17 was a target gene of GhBES1 and play an important role in fiber cell elongation by regulating the organization of microtubule and microfilament cytoskeleton. It provided a link between BRs and cytoskeleton in fiber cell elongation and a potential gene to improve the fiber quality, and shed light on understanding the action mechanism of BRs.

GhMAX2 Contributes to Auxin-Mediated Fiber Elongation in Cotton (Gossypium hirsutum).

Strigolactones (SLs) represent a new group of phytohormones that play a pivotal role in the regulation of plant shoot branching and the development of adventitious roots. In cotton (Gossypium hirsutum, Gh), SLs play a crucial role in the regulation of fiber cell elongation and secondary cell wall thickness. However, the underlying molecular mechanisms of SL signaling involved in fiber cell development are largely unknown. In this study, we report two SL-signaling genes, GhMAX2-3 and GhMAX2-6, which positively regulate cotton fiber elongation. Further protein-protein interaction and degradation assays showed that the repressor of the auxin cascade GhIAA17 serves as a substrate for the F-box E3 ligase GhMAX2. The in vivo ubiquitination assay suggested that GhMAX2-3 and GhMAX2-6 ubiquitinate GhIAA17 and coordinately degrade GhIAA17 with GhTIR1. The findings of this investigation offer valuable insights into the roles of GhMAX2-mediated SL signaling in cotton and establish a solid foundation for future endeavors aimed at optimizing cotton plant cultivation.

Strigolactone-induced degradation of SMXL7 and SMXL8 contributes to gibberellin- and auxin-mediated fiber cell elongation in cotton.

Cotton (Gossypium) fiber length, a key trait determining fiber yield and quality, is highly regulated by a class of recently identified phytohormones, strigolactones (SLs). However, the underlying molecular mechanisms of SL signaling involved in fiber cell development are largely unknown. Here, we show that the SL signaling repressors MORE AXILLARY GROWTH2-LIKE7 (GhSMXL7) and GhSMXL8 negatively regulate cotton fiber elongation. Specifically, GhSMXL7 and GhSMXL8 inhibit the polyubiquitination and degradation of the gibberellin (GA)-triggered DELLA protein (GhSLR1). Biochemical analysis revealed that GhSMXL7 and GhSMXL8 physically interact with GhSLR1, which interferes with the association of GhSLR1 with the E3 ligase GA INSENSITIVE2 (GhGID2), leading to the repression of GA signal transduction. GhSMXL7 also interacts with the transcription factor GhHOX3, preventing its binding to the promoters of essential fiber elongation regulatory genes. Moreover, both GhSMXL7 and GhSMXL8 directly bind to the promoter regions of the AUXIN RESPONSE FACTOR (ARF) genes GhARF18-10A, GhARF18-10D, and GhARF19-7D to suppress their expression. Cotton plants in which GhARF18-10A, GhARF18-10D, and GhARF19-7D transcript levels had been reduced by virus-induced gene silencing (VIGS) displayed reduced fiber length compared with control plants. Collectively, our findings reveal a mechanism illustrating how SL integrates GA and auxin signaling to coordinately regulate plant cell elongation at the single-cell level.

Exploring the plasmodesmata callose-binding protein gene family in upland cotton: unraveling insights for enhancing fiber length.

Plasmodesmata are transmembrane channels embedded within the cell wall that can facilitate the intercellular communication in plants. Plasmodesmata callose-binding (PDCB) protein that associates with the plasmodesmata contributes to cell wall extension. Given that the elongation of cotton fiber cells correlates with the dynamics of the cell wall, this protein can be related to the cotton fiber elongation. This study sought to identify PDCB family members within the Gossypium. hirsutum genome and to elucidate their expression profiles. A total of 45 distinct family members were observed through the identification and screening processes. The analysis of their physicochemical properties revealed the similarity in the amino acid composition and molecular weight across most members. The phylogenetic analysis facilitated the construction of an evolutionary tree, categorizing these members into five groups mainly distributed on 20 chromosomes. The fine mapping results facilitated a tissue-specific examination of group V, revealing that the expression level of GhPDCB9 peaked five days after flowering. The VIGS experiments resulted in a marked decrease in the gene expression level and a significant reduction in the mature fiber length, averaging a shortening of 1.43-4.77 mm. The results indicated that GhPDCB9 played a pivotal role in the cotton fiber development and served as a candidate for enhancing cotton yield.

GhATL68b regulates cotton fiber cell development by ubiquitinating the enzyme required for β-oxidation of polyunsaturated fatty acids

E3 ligases are key enzymes required for protein degradation. Here, we identified a C3H2C3 RING domain-containing E3 ubiquitin ligase gene named GhATL68b. It is preferentially and highly expressed in developing cotton fiber cells and shows greater conservation in plants than in animals or archaea. The four orthologous copies of this gene in various diploid cottons and eight in the allotetraploid G. hirsutum were found to have originated from a single common ancestor that can be traced back to Chlamydomonas reinhardtii at about 992 million years ago. Structural variations in the GhATL68b promoter regions of G. hirsutum, G. herbaceum, G. arboreum, and G. raimondii are correlated with significantly different methylation patterns. Homozygous CRISPR-Cas9 knockout cotton lines exhibit significant reductions in fiber quality traits, including upper-half mean length, elongation at break, uniformity, and mature fiber weight. In vitro ubiquitination and cell-free protein degradation assays revealed that GhATL68b modulates the homeostasis of 2,4-dienoyl-CoA reductase, a rate-limiting enzyme for the β-oxidation of polyunsaturated fatty acids (PUFAs), via the ubiquitin proteasome pathway. Fiber cells harvested from these knockout mutants contain significantly lower levels of PUFAs important for production of glycerophospholipids and regulation of plasma membrane fluidity. The fiber growth defects of the mutant can be fully rescued by the addition of linolenic acid (C18:3), the most abundant type of PUFA, to the ovule culture medium. This experimentally characterized C3H2C3 type E3 ubiquitin ligase involved in regulating fiber cell elongation may provide us with a new genetic target for improved cotton lint production.

GhFAD3-4 Promotes Fiber Cell Elongation and Cell Wall Thickness by Increasing PI and IP3 Accumulation in Cotton.

The omega-3 fatty acid desaturase enzyme gene FAD3 is responsible for converting linoleic acid to linolenic acid in plant fatty acid synthesis. Despite limited knowledge of its role in cotton growth, our study focused on GhFAD3-4, a gene within the FAD3 family, which was found to promote fiber elongation and cell wall thickness in cotton. GhFAD3-4 was predominantly expressed in elongating fibers, and its suppression led to shorter fibers with reduced cell wall thickness and phosphoinositide (PI) and inositol triphosphate (IP3) levels. Transcriptome analysis of GhFAD3-4 knock-out mutants revealed significant impacts on genes involved in the phosphoinositol signaling pathway. Experimental evidence demonstrated that GhFAD3-4 positively regulated the expression of the GhBoGH3B and GhPIS genes, influencing cotton fiber development through the inositol signaling pathway. The application of PI and IP6 externally increased fiber length in GhFAD3-4 knock-out plants, while inhibiting PI led to a reduced fiber length in GhFAD3-4 overexpressing plants. These findings suggest that GhFAD3-4 plays a crucial role in enhancing fiber development by promoting PI and IP3 biosynthesis, offering the potential for breeding cotton varieties with superior fiber quality.

PagEXPA1 combines with PagCDKB2;1 to regulate plant growth and the elongation of fibers in Populus alba × Populus glandulosa

Expansins are important plant cell wall proteins. They can loosen and soften the cell walls and lead to wall extension and cell expansion. To investigate their role in wood formation and fiber elongation, the PagEXPA1 that highly expressed in cell differentiation and expansion tissues was cloned from 84K poplar (Populus alba × P. glandulosa). The subcellular localization showed that PagEXPA1 located in the cell wall and it was highly expressed in primary stems and young leaves. Compared with non-transgenic 84K poplar, overexpression of PagEXPA1 can promote plant-growth, lignification, and fiber cell elongation, while PagEXPA1 Cas9-editing mutant lines exhibited the opposite phenotype. Transcriptome analysis revealed that DEGs were mainly enriched in some important processes, which are associated with cell wall formation and cellulose synthesis. The protein interaction prediction and expression analysis showed that PagCDKB2:1 and PagEXPA1 might have an interaction relationship. The luciferase complementary assay and bimolecular fluorescence complementary assay validated that PagEXPA1 can combined with PagCDKB2;1. So they promoted the expansion of xylem vascular tissues and the development of poplar though participating in the regulation of cell division and differentiation by programming the cell-cycle. It provides good foundation for molecular breeding of fast-growing and high-quality poplar varieties.

Cotton sphingosine kinase GhLCBK1 participates in fiber cell elongation by affecting sphingosine-1-phophate and auxin synthesis

Sphingolipids serve as essential components of biomembrane and possess significant bioactive properties. Sphingosine-1-phophate (S1P) plays a key role in plant resistance to stress, but its specific impact on plant growth and development remains to be fully elucidated. Cotton fiber cells are an ideal material for investigating the growth and maturation of plant cells. In this study, we examined the content and composition of sphingosine (Sph) and S1P throughout the progression of fiber cell development. The content of S1P elevated gradually during fiber elongation but declined during the transition stage. Exogenous application of S1P promoted fiber elongation while using of FTY720 (an antagonist of S1P), and DMS (an inhibitor of LCBK) hindered fiber elongation. Cotton Long Chain Base Kinase 1 (GhLCBK1) was notably expressed during the fiber elongation stage, containing all conserved domains of LCBK protein and localized in the endoplasmic reticulum. Overexpression GhLCBK1 increased the S1P content and promoted fiber elongation while retarded secondary cell wall (SCW) deposition. Conversely, downregulation of GhLCBK1 reduced the S1P levels, and suppressed fiber elongation, and accelerated SCW deposition. Transcriptome analysis revealed that upregulating GhLCBK1 or applying S1P induced the expression of GhEXPANSIN and auxin related genes. Furthermore, the levels of IAA were elevated and reduced in the fibers when up-regulating or down-regulating GhLCBK1, respectively. Our investigation demonstrated that GhLCBK1 and its product S1P facilitated the elongation of fiber cells by affecting auxin biosynthesis. This study contributes novel insights into the intricate regulatory pathways involved in fiber cell elongation, identifying GhLCBK1 as a potential target gene and laying the groundwork for enhancing fiber quality via genetic manipulation.

Cotton BLH1 and KNOX6 antagonistically modulate fiber elongation via regulation of linolenic acid biosynthesis

BEL1-LIKE HOMEODOMAIN (BLH) proteins are known to function in various plant developmental processes. However, the role of BLHs in regulating plant cell elongation is still unknown. Here, we identify a BLH gene, GhBLH1, that positively regulates fiber cell elongation. Combined transcriptomic and biochemical analyses reveal that GhBLH1 enhances linolenic acid accumulation to promote cotton fiber cell elongation by activating the transcription of GhFAD7A-1 via binding of the POX domain of GhBLH1 to the TGGA cis-element in the GhFAD7A-1 promoter. Knockout of GhFAD7A-1 in cotton significantly reduces fiber length, whereas overexpression of GhFAD7A-1 results in longer fibers. The K2 domain of GhKNOX6 directly interacts with the POX domain of GhBLH1 to form a functional heterodimer, which interferes with the transcriptional activation of GhFAD7A-1 via the POX domain of GhBLH1. Overexpression of GhKNOX6 leads to a significant reduction in cotton fiber length, whereas knockout of GhKNOX6 results in longer cotton fibers. An examination of the hybrid progeny of GhBLH1 and GhKNOX6 transgenic cotton lines provides evidence that GhKNOX6 negatively regulates GhBLH1-mediated cotton fiber elongation. Our results show that the interplay between GhBLH1 and GhKNOX6 modulates regulation of linolenic acid synthesis and thus contributes to plant cell elongation.

GhWDL3 is involved in the formation and development of fiber cell morphology in upland cotton (Gossypium hirsutum L.)

BackgroundCotton fiber is a model tissue for studying microtubule-associated proteins (MAPs). The Xklp2 (TPX2) proteins that belong to the novel MAPs member mainly participate in the formation and development of microtubule (MT). However, there is a lack of studies concerning the systematic characterization of the TPX2 genes family in cotton. Therefore, the identification and portrayal of G. hirsutum TPX2 genes can provide key targets for molecular manipulation in the breeding of cotton fiber improvement.ResultIn this study, TPX2 family genes were classified into two distinct subclasses TPXLs and MAP genes WAVE DAMPENED2-LIKE (WDLs) and quite conservative in quantity. GhWDL3 was significantly up-regulated in 15 days post anthesis fibers of ZRI-015 (an upland cotton with longer and stronger fiber). GhWDL3 promotes all stem hairs to become straight when overexpressed in Arabidopsis, which may indirectly regulate cotton fiber cell morphology during fiber development. Virus induced gene silencing (VIGS) results showed that GhWDL3 inhibited fiber cell elongation at fiber development periods through regulating the expression of cell wall related genes.ConclusionThese results reveal that GhWDL3 regulated cotton fiber cell elongation and provide crucial information for the further investigation in the regulatory mechanisms/networks of cotton fiber length.

Gibberellic acid promotes single-celled fiber elongation through the activation of two signaling cascades in cotton

The agricultural green revolution spectacularly enhanced crop yield through modification of gibberellin (GA) signaling. However, in cotton, the GA signaling cascades remain elusive, limiting our potential to cultivate new cotton varieties and improve yield and quality. Here, we identified that GA prominently stimulated fiber elongation through the degradation of DELLA protein GhSLR1, thereby disabling GhSLR1's physical interaction with two transcription factors, GhZFP8 and GhBLH1. Subsequently, the resultant free GhBLH1 binds to GhKCS12 promoter and activates its expression to enhance VLCFAs biosynthesis. With a similar mechanism, the free GhZFP8 binds to GhSDCP1 promoter and activates its expression. As a result, GhSDCP1 upregulates the expression of GhPIF3 gene associated with plant cell elongation. Ultimately, the two parallel signaling cascades synergistically promote cotton fiber elongation. Our findings outline the mechanistic framework that translates the GA signal into fiber cell elongation, thereby offering a roadmap to improve cotton fiber quality and yield.

Fibroblast growth factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac.

The spheroidal shape of the eye lens is crucial for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that, in the mouse lens, membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating that lamellipodium formation is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controlling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin and actin reduced the height of both early and later fibers, indicating that elongation of these fibers relies on actomyosin contractility. Consistent with this, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose that it does so through regulation of Rho activity.

GhSMO2-2 is regulated by brassinosteroid signal and involved in cotton fiber elongation via influencing phytosterol and sphingolipid biosynthesis

Cotton fiber cell is an extremely elongated single cell and is regarded as an ideal material to study the growth and development of plant cell. Phytohormone brassinosteroids (BRs) play crucial roles in fiber cell development. However, its action mechanism in fiber growth is largely unknown. In this study, we identified a homologue of Arabidopsis SMO2–2 (Sterol C-4α Methyl Oxidase), GhSMO2–2, in upland cotton (Gossypium hirsutum L.), which predominantly expressed in fiber cell and peaked at the rapid elongation stage, and responded to BR signal. The GhBES1, a transcription factor in BR signaling could directly bind to the promoter of GhSMO2–2 and promoted its expression. Overexpression of GhSMO2–2 significantly promoted fiber cell elongation and phytosterol synthesis in cotton, and elevated some sphingolipid species that was important for fiber elongation. On the contrary, down-regulating GhSMO2–2 suppressed fiber elongation and blocked these chemicals accumulation. These results indicated that GhSMO2–2 is an important gene involved in fiber cell elongation, and is valuable for genetic engineering to improve fiber quality and yield. Taken together, our study revealed that BR regulated fiber cell elongation by influencing phytosterol and sphingolipid biosynthesis, the key components of membrane lipid raft and provided a new clue for further revealing the function and mechanism of phytosterols, sphingolipids, and BRs in plant cell development.

LIPID TRANSFER PROTEIN4 regulates cotton ceramide content and activates fiber cell elongation.

Cell elongation is a fundamental process for plant growth and development. Studies have shown lipid metabolism plays important role in cell elongation; however, the related functional mechanisms remain largely unknown. Here, we report that cotton (Gossypium hirsutum) LIPID TRANSFER PROTEIN4 (GhLTP4) promotes fiber cell elongation via elevating ceramides (Cers) content and activating auxin-responsive pathways. GhLTP4 was preferentially expressed in elongating fibers. Over-expression and down-regulation of GhLTP4 led to longer and shorter fiber cells, respectively. Cers were greatly enriched in GhLTP4-overexpressing lines and decreased dramatically in GhLTP4 down-regulating lines. Moreover, auxin content and transcript levels of indole-3-acetic acid (IAA)-responsive genes were significantly increased in GhLTP4-overexpressing cotton fibers. Exogenous application of Cers promoted fiber elongation, while NPA (N-1-naphthalic acid, a polar auxin transport inhibitor) counteracted the promoting effect, suggesting that IAA functions downstream of Cers in regulating fiber elongation. Furthermore, we identified a basic helix-loop-helix transcription factor, GhbHLH105, that binds to the E-box element in the GhLTP4 promoter region and promotes the expression of GhLTP4. Suppression of GhbHLH105 in cotton reduced the transcripts level of GhLTP4, resulting in smaller cotton bolls and decreased fiber length. These results provide insights into the complex interactions between lipids and auxin-signaling pathways to promote plant cell elongation.

A cell wall-localized β-1,3-glucanase promotes fiber cell elongation and secondary cell wall deposition.

β-1,3-glucanase functions in plant physiological and developmental processes. However, how β-1,3-glucanase participates in cell wall development remains largely unknown. Here, we answered this question by examining the role of GhGLU18, a β-1,3-glucanase, in cotton (Gossypium hirsutum) fibers, in which the content of β-1,3-glucan changes dynamically from 10% of the cell wall mass at the onset of secondary wall deposition to <1% at maturation. GhGLU18 was specifically expressed in cotton fiber with higher expression in late fiber elongation and secondary cell wall (SCW) synthesis stages. GhGLU18 largely localized to the cell wall and was able to hydrolyze β-1,3-glucan in vitro. Overexpression of GhGLU18 promoted polysaccharide accumulation, cell wall reconstruction, and cellulose synthesis, which led to increased fiber length and strength with thicker cell walls and shorter pitch of the fiber helix. However, GhGLU18-suppressed cotton resulted in opposite phenotypes. Additionally, GhGLU18 was directly activated by GhFSN1 (fiber SCW-related NAC1), a NAC transcription factor reported previously as the master regulator in SCW formation during fiber development. Our results demonstrate that cell wall-localized GhGLU18 promotes fiber elongation and SCW thickening by degrading callose and enhancing polysaccharide metabolism and cell wall synthesis.

A conserved brassinosteroid-mediated BES1-CERP-EXPA3 signaling cascade controls plant cell elongation

Continuous plant growth is achieved by cell division and cell elongation. Brassinosteroids control cell elongation and differentiation throughout plant life. However, signaling cascades underlying BR-mediated cell elongation are unknown. In this study, we introduce cotton fiber, one of the most representative single-celled tissues, to decipher cell-specific BR signaling. We find that gain of function of GhBES1, a key transcriptional activator in BR signaling, enhances fiber elongation. The chromatin immunoprecipitation sequencing analysis identifies a cell-elongation-related protein, GhCERP, whose transcription is directly activated by GhBES1. GhCERP, a downstream target of GhBES1, transmits the GhBES1-mediated BR signaling to its target gene, GhEXPA3-1. Ultimately, GhEXPA3-1 promotes fiber cell elongation. In addition, inter-species functional analysis of the BR-mediated BES1-CERP-EXPA3 signaling cascade also promotes Arabidopsis root and hypocotyl growth. We propose that the BES1-CERP-EXPA3 module may be a broad-spectrum pathway that is universally exploited by diverse plant species to regulate BR-promoted cell elongation.

Correction to: Strigolactones act downstream of gibberellins to regulate fiber cell elongation and cell wall thickness in cotton (Gossypium hirsutum)

Correction to: Strigolactones act downstream of gibberellins to regulate fiber cell elongation and cell wall thickness in cotton (Gossypium hirsutum)

Down-regulating a fiber-specific KCR like gene GhKCRL1 suppressed fiber elongation through blocking the synthesis of sphingolipids in fiber cell

Cotton is an important natural fiber crop in the world. Cotton fiber cell is an extremely elongated single-cell trichome of seeds. Therefore, the fiber cell is an ideal model for studying plant cell elongation (polar expansion) and secondary wall deposition. Moreover, the two processes determine the quality (length, strength and fineness) of mature cotton fiber. However, the regulatory mechanism of fiber elongation remains unclear. Ligon lintless-1 ( Li-1 ) mutant is a fiber elongation mutant and a good material to study fiber elongation. In the present study, through analyzing the different expression genes in 10-DPA (day post anthesis) fiber cell of Li-1 mutant and its wild type (TM-1), we found a KCR (3-Ketoacyl-Coenzyme A Reductase) like gene, GhKCRL1 , was strikingly down-regulated in Li-1 mutant. GhKCRL1 shared low sequence identity with the 17 beta-hydroxysteroid dehydrogenase 12 of animal and the reported GhKCR1, GhKCR2, and GhKCR3 of upland cotton. GhKCRL1 was specifically expressed in fiber cells and its expression level peaked in 10-DPA fiber cells. GhKCRL1 is located in the endoplasmic reticulum . Down-regulating the expression of GhKCRL1 suppressed fiber elongation and significantly shortened mature fiber length. The sphingolipids contained VLCFA and LCFA strikingly declined in RNAi fiber cells. Consistently, the expression levels of most genes involved in sphingolipid biosynthesis and very long chain fatty acid (VLCFA) biosynthesis decreased in GhKCRL1 down-regulated cotton fibers. And the exogenous application of VLCFA (C24 FA) could rescue the elongation of GhKCRL1 down-regulated fiber cells. Taken together, the results revealed that the fiber-specific GhKCRL1 play some roles in cotton fiber elongation by regulating sphingolipid biosynthesis. Pattern diagram of the GhKCRL regulating fiber elongation. • GhKCRL1 is a novel KCR gene in upland cotton. • GhKCRL1 specifically expressed in fibers cells. • Down-regulating GhKCRL1 expression suppressed fiber cell elongation. • Down-regulating GhKCRL1 blocking the synthesis of sphingolipids in fiber cell.