Strigolactones modulate cotton fiber elongation and secondary cell wall thickening

Cotton is one of the most important economic crops in the world,and it is a major source of fiber in the textile industry.Strigolactones(SLs)are a class of carotenoid-derived plant hormones involved in many processes of plant growth and development,although the functions of SL in fiber development remain largely unknown.Here,we found that the endogenous SLs were significantly higher in fibers at 20 days post-anthesis(DPA).Exogenous SLs significantly increased fiber length and cell wall thickness.Furthermore,we cloned three key SL biosynthetic genes,namely GhD27,GhMAX3,and GhMAX4,which were highly expressed in fibers,and subcellular localization analyses revealed that GhD27,GhMAX3,and GhMAX4 were localized in the chloroplast.The exogenous expression of GhD27,GhMAX3,and GhMAX4 complemented the physiological phenotypes of d27,max3,and max4 mutations in Arabidopsis,respectively.Knockdown of GhD27,GhMAX3,and GhMAX4 in cotton resulted in increased numbers of axillary buds and leaves,reduced fiber length,and significantly reduced fiber thickness.These findings revealed that SLs participate in plant growth,fiber elongation,and secondary cell wall formation in cotton.These results provide new and effective genetic resources for improving cotton fiber yield and plant architecture.

Genetic dissection and origin of pleiotropic loci underlying multilevel fiber quality traits in upland cotton(Gossypium hirsutum L.)

Cotton fiber quality is a persistent concern that determines planting benefits and the quality of finished textile products.However,the limitations of measurement instruments have hindered the accurate evaluation of some important fiber characteristics such as fiber maturity,fineness,and neps,which in turn has impeded the genetic improvement and industrial utilization of cotton fiber.Here,12 single fiber quality traits were measured using Advanced Fiber Information System(AFIS)equipment among 383 accessions of upland cotton(Gossypium hirsutum L.).In addition,eight conventional fiber quality traits were assessed by the High Volume Instrument(HVI)System.Genome-wide association study(GWAS),linkage disequilibrium(LD)block genotyping and functional identification were conducted sequentially to uncover the associated elite loci and candidate genes of fiber quality traits.As a result,the previously reported pleiotropic locus FL_D11 regulating fiber length-related traits was identified in this study.More importantly,three novel pleiotropic loci(FM_A03,FF_A05,and FN_A07)regulating fiber maturity,fineness and neps,respectively,were detected based on AFIS traits.Numerous highly promising candidate genes were screened out by integrating RNA-seq and qRT-PCR analyses,including the reported GhKRP6 for fiber length,the newly identified GhMAP8 for maturity and GhDFR for fineness.The origin and evolutionary analysis of pleiotropic loci indicated that the selection pressure on FL_D11,FM_A03 and FF_A05 increased as the breeding period approached the present and the origins of FM_A03 and FF_A05 were traced back to cotton landraces.These findings reveal the genetic basis underlying fiber quality and provide insight into the genetic improvement and textile utilization of fiber in G.hirsutum.

The DUF579 proteins GhIRX15s regulate cotton fiber development by interacting with proteins involved in xylan synthesis

Cotton provides the most abundant natural fiber for the textile industry.The mature cotton fiber largely consists of secondary cell walls with the highest proportion of cellulose and a small amount of hemicellulose and lignin.To dissect the roles of hemicellulosic polysaccharides during fiber development,four IRREGULAR XYLEM 15(IRX15)genes,GhIRX15-1/-2/-3/-4,were functionally characterized in cotton.These genes encode DUF579 domain-containing proteins,which are homologs of AtIRX15 involved in xylan biosynthesis.The four GhIRX15 genes were predominantly expressed during fiber secondary wall thickening,and the encoded proteins were localized to the Golgi apparatus.Each GhIRX15 gene could restore the xylan deficient phenotype in the Arabidopsis irx15irx15l double mutant.Silencing of GhIRX15s in cotton resulted in shorter mature fibers with a thinner cell wall and reduced cellulose content as compared to the wild type.Intriguingly,GhIRX15-2 and GhIRX15-4 formed homodimers and heterodimers.In addition,the GhIRX15s showed physical interaction with glycosyltransferases GhGT43C,GhGT47A and GhGT47B,which are responsible for synthesis of the xylan backbone and reducing end sequence.Moreover,the GhIRX15s can form heterocomplexes with enzymes involved in xylan modification and side chain synthesis,such as GhGUX1/2,GhGXM1/2 and GhTBL1.These findings suggest that GhIRX15s participate in fiber xylan biosynthesis and modulate fiber development via forming large multiprotein complexes.

Identification of new cotton fiber-quality QTL by multiple genomic analyses and development of markers for genomic breeding

Cotton fiber is one of the main raw materials for the textile industry.In recent years,many cotton fiber quality QTL have been identified,but few were applied in breeding.In this study,a genome wide association study(GWAS)of fiber-quality traits in 265 upland cotton breeding intermediate lines(GhBreeding),combined with genome-wide selective sweep analysis(GSSA)and genomic selection(GS),revealed 25 QTL.Most of these QTL were ignored by only using GWAS.The CRISPR/Cas9 mutants of GhMYB_D13 had shorter fiber,which indicates the credibility of QTL to a certain extent.Then these QTL were verified in other cotton natural populations,5 stable QTL were found having broad potential for application in breeding.Additionally,among these 5 stable QTL,superior genotypes of 4 showed an enrichment in most improved new varieties widely cultivated currently.These findings provide insights for how to identify more QTL through combined multiple genomic analysis to apply in breeding.

Exogenous application of bio-stimulants and growth retardants improve nutrient absorption and fiber quality in upland cotton

Background Natural and synthetic plant growth regulators are essential for plant health,likewise these regulators also play a role in increasing organic production productivity and improving quality and yield stability.In the present study,we have evaluated the effects of foliar applied plant growth regulators,i.e.,moringa leaf extract(MLE)and mepiquat chloride(MC)alone and in combination MC and MLE on the conventional cotton cultivar(CIM 573)and transgenic one(CIM 598).The growth regulators were applied at the start of bloom,45 and 90 days after blooming.Results The application of MC and MLE at 90 days after blooming significantly improved the relative growth rate,net assimilation rate,the number of bolls per plant,and seed cotton yield.Likewise,the combined application of MLE and MC at 90 days after blooming significantly boosted the nitrogen uptake in locules,as well as the phosphorus and potassium uptake in the leaves of both cotton cultivars.The application of MLE alone has considerably improved the nitrogen uptake in leaves,and phosphorus and potassium contents in locules of Bt and conventional cotton cultivars.Similarly,Bt cotton treated with MLE at 90 days after blooming produced significantly higher ginning out turn and oil contents.Treatment in combination(MLE+MC)at 90 days after blooming produced considerably higher micronaire value,fiber strength,and staple length in conventional cultivar.Conclusion The natural growth enhancer,MLE is a rich source of minerals and zeatin,improving the nutrient absorption and quality of cotton fiber in both conventional and Bt cotton cultivars.

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

Background Cotton 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 manipula-tion in the breeding of cotton fiber improvement.Result In this study,TPX2 family genes were classified into two distinct subclasses TPXLs and MAP genes WAVE DAMP-ENED2-LIKE(WDLs)and quite conservative in quantity.GhWDL3 was significantly up-regulated in 15 days post anthe-sis 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.Conclusion These 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.

Combining ability of Egyptian cotton(Gossypium barbadense L.)reveals genetic potential for improved yield and fiber quality

Background As the most widely cultivated fiber crop,cotton production depends on hybridization to unlock the yield potential of current varieties.A deep understanding of genetic dissection is crucial for the cultivation of enhanced hybrid plants with desired traits,such as high yield and fine fiber quality.In this study,the general combining ability(GCA)and specific combining ability(SCA)of yield and fiber quality of nine cotton parents(six lines and three testers)and eighteen F1 crosses produced using a line×tester mating design were analyzed.Results The results revealed significant effects of genotypes,parents,crosses,and interactions between parents and crosses for most of the studied traits.Moreover,the effects of both additive and non-additive gene actions played a notably significant role in the inheritance of most of the yield and fiber quality attributes.The F1 hybrids of(Giza 90×Aust)×Giza 86,Uzbekistan 1×Giza 97,and Giza 96×Giza 97 demonstrated superior performance due to their favorable integration of high yield attributes and premium fiber quality characteristics.Path analysis revealed that lint yield has the highest positive direct effect on seed cotton yield,while lint percentage showed the highest negative direct effect on seed cotton yield.Principal component analysis identified specific parents and hybrids associated with higher cotton yield,fiber quality,and other agronomic traits.Conclusion This study provides insights into identifying potential single-and three-way cross hybrids with superior cotton yield and fiber quality characteristics,laying a foundation for future research on improving fiber quality in cotton.

Growth, yield and fiber quality characteristics of Bt and non-Bt cotton cultivars in response to boron nutrition

Background Boron(B)deficiency is an important factor for poor seed cotton yield and fiber quality.However,it is often missing in the plant nutrition program,particularly in developing countries.The current study investigated B’s effect on growth,yield,and fiber quality of Bt(CIM-663)and non-Bt(Cyto-124)cotton cultivars.The experimental plan consisted of twelve treatments:Control(CK);B at 1 mg·kg^(−1) soil application(SB1);2 mg·kg^(−1) B(SB2);3 mg·kg^(−1) B(SB3);0.2%B foliar spray(FB1);0.4%B foliar spray(FB2);1 mg·kg^(−1) B+0.2%B foliar spray(SB1+FB1);1 mg·kg^(−1) B+0.4%B foliar spray(SB1+FB2);2 mg·kg^(−1) B+0.2%B foliar spray(SB2+FB1);2 mg·kg^(−1) B+0.4%B foliar spray(SB2+FB2);3 mg·kg^(−1) B+0.2%B foliar spray(SB3+FB1);3 mg·kg^(−1) B+0.4%B foliar spray(SB3+FB2).Each treat-ment has three replications,one pot having two plants per replication.Results B nutrition at all levels and methods of application significantly(P≤0.05)affected the growth,physiological,yield,and fiber quality characteristics of both cotton cultivars.However,SB2 either alone or in combination with foliar spray showed superiority over others,particularly in the non-Bt cultivar which responded better to B nutrition.Maxi-mum improvement in monopodial branches(345%),sympodial branches(143%),chlorophyll-a(177%),chlorophyll-b(194%),photosynthesis(169%),and ginning out turn(579%)in the non-Bt cultivar was found with SB2 compared with CK.In Bt cultivar,although no consistent trend was found but integrated use of SB3 with foliar spray performed relatively better for improving cotton growth compared with other treatments.Fiber quality characteristics in both cultivars were improved markedly but variably with different B treatments.Conclusion B nutrition with SB2 either alone or in combination with foliar spray was found optimum for improving cotton’s growth and yield characteristics.

GhIQD10 interacts with GhCaM7 to control cotton fiber elongation via calcium signaling

IQ67-domain(IQD)proteins function in plant defense and in organ development.The mechanisms by which they influence cotton fiber development are unknown.In the present study,GhIQD10 was expressed mainly in the transition period of cotton fiber development,and GhIQD10-overexpression lines showed shorter fibers.GhIQD10 interacted with GhCaM7 and the interaction was inhibited by Ca^(2+).In in vitro ovule culture,Ca^(2+)rescued the shorter-fiber phenotype of GhIQD10-overexpression lines,which were insensitive to the Ca^(2+)channel inhibitor verapamil and the Ca^(2+)pool release channel blocker 2-aminoethoxydiphenyl borate.We conclude that GhIQD10 affects cotton fiber elongation via Ca^(2+)signaling by interacting with GhCaM7.Brassinosteroid(BR)biosynthesis and signaling genes were up-regulated in GhIQD10-overexpression lines.Fiber development in these lines was not affected by epibrassinolide or the BR biosynthesis inhibitor brassinozole,indicating that the influence of GhIQD10 on fiber elongation was not associated with BR.

Cotton pads-derived carbon materials/reduced graphene oxide modified with polypyrrole for electrode of supercapacitors

This study investigates the influence of electropolymerization conditions on the deposition of polypyrrole(PPy)onto cotton-derived carbon fiber(CF)modified with reduced graphene oxide(rGO)for supercapacitors applications using an experimental/theorical approach.The surface modification of CF by rGO and/or by PPy electrodeposited at 10,25 and 50 mV s^(-1) was thoroughly examined physicochemical and electrochemically.Composite electrodes comprising CF-rGo-PPy,synthesized via electropolymerization at 25 mV s^(-1),demonstrated a remarkable increase in capacitance,showcasing~742 F g^(-1) compared to 153 F g^(-1) for CF.SEM,N_(2)-surface area,XPS,and TD-DFT approach revealed that the higher capacitance observed in CF-rGo-PPy electrodes underscores the influence of morphology and charged nitrogen species on the electrochemical performance of these modified electrodes.Notably,this electrode material achieves a specific capacitance retention of~96%of their initial capacitance after 10000 cycles at 0.5 A g^(-1) measured in a two-electrodes cell configuration.This work also discusses the influence of the scan rate used for pyrrole electropolymerization on the pseudocapacitance contribution of PPy and its possible effect on the porosity of the material.These results highlight the importance of appropriate electropolymerization conditions that allow obtaining the synergistic effect between CF,rGO and PPy.

Flavanone and flavonoid hydroxylase genes regulate fiber color formation in naturally colored cotton

Using naturally colored cotton(NCC)can eliminate dyeing,printing and industrial processing,and reduce sewage discharge and energy consumption.Proanthocyanidins(PAs),the primary coloration components in brown fibers,are polyphenols formed by oligomers or polymers of flavan-3-ol units derived from anthocyanidins.Three essential structural genes for flavanone and flavonoid hydroxylation encoding flavanone-3-hydroxylase(F3H),flavonoid 3’-hydroxylase(F3’H)and flavonoid 3’5’-hydroxylase(F3’5’H)are initially committed in the flavonoid biosynthesis pathway to produce common precursors.The three genes were all expressed predominantly in developing fibers of NCCs,and their expression patterns varied temporally and spatially among NCC varieties.In GhF3Hi,GhF3’Hi and GhF3’5’Hi silenced lines of NCC varieties XC20 and ZX1,the expression level of the three genes decreased in developing cotton fiber,negatively correlated with anthocyanidin content and fiber color depth.Fiber color depth and type in RNAi lines changed with endogenous gene silencing efficiency and expression pattern,the three hydroxylase genes functioned in fiber color formation.GhF3H showed functional differentiation among NCC varieties and GhF3’H acted in the accumulation of anthocyanin in fiber.Compared with GhF3’H,GhF3’5’H was expressed more highly in brown fiber with a longer duration of expression and caused lighter color of fibers in GhF3’5’H silenced lines.These three genes regulating fiber color depth and type could be used to improve these traits by genetic manipulation.

Comparative transcriptome and lipidome reveal that a low K^(+) signal effectively alleviates the effect induced by Ca^(2+) deficiency in cotton fibers

Calcium(Ca^(2+))plays an important role in determining plant growth and development because it maintains cell wall and membrane integrity.Therefore,understanding the role of Ca^(2+)in carbon and lipid metabolism could provide insights into the dynamic changes in cell membranes and cell walls during the rapid elongation of cotton fibers.In the present study,we found that the lack of Ca^(2+)promoted fiber elongation and rapid ovule expansion,but it also caused tissue browning in the ovule culture system.RNA-sequencing revealed that Ca^(2+)deficiency induced cells to be highly oxidized,and the expression of genes related to carbon metabolism and lipid metabolism was activated significantly.All gene members of nine key enzymes involved in glycolysis were up-regulated,and glucose was significantly reduced in Ca^(2+)deficiency-treated tissues.Ca^(2+)deficiency adjusted the flowing of glycolysis metabolic.However,low K^(+)recovered the expression levels of glycolysis genes and glucose content caused by Ca^(2+)deficiency.Electrospray ionizationtandem mass spectrometry technology was applied to uncover the dynamic profile of lipidome under Ca^(2+)and K^(+)interacted conditions.Ca^(2+)deficiency led to the decrease of fatty acid(FA),diacylglycerol(DAG),glycolipid and the significant increase of triacylglycerol(TAG),phospholipid phosphatidylethanolamine(PE),phosphatidylglycerol(PG),and PC(phosphatidylcholine).Low K^(+)restored the contents of FA,phospholipids,and glycolipids,effectively relieved the symptoms caused by Ca^(2+)deficiency,and recovered the development of fiber cells.This study revealed dynamic changes in transcript and metabolic levels and uncovered the signaling interaction of Ca^(2+)deficiency and low K^(+)in glycolysis and lipid metabolism during fiber development.

Fiber-specific increase of carotenoid content promotes cotton fiber elongation by increasing abscisic acid and ethylene biosynthesis

Cotton fiber is a raw material for the global textile industry and fiber quality is essential to its industrial application.Carotenoids are plant secondary metabolites that may serve as dietary components,regulate light harvesting,and scavenge reactive oxygen species.Although carotenoids accumulate predominantly in rapidly elongating cotton fibers,their roles in cotton fiber development remain poorly understood.In this study,a fiber-specific promoter proSCFP was applied to drive the expression of GhOR1Del,a positive regulator of carotenoid accumulation,to upregulate the carotenoid level in cotton fiber in planta.Fiber length,strength,and fineness were increased in proSCFP:GhOR1Del transgenic cotton and abscisic acid(ABA)and ethylene contents were increased in elongating fibers.The ABA downstream regulator GhbZIP27a stimulated the expression of the ethylene synthase gene GhACO3 by binding to its promoter,suggesting that ABA promoted fiber elongation by increasing ethylene production.These findings suggest the involvement of carotenoids and ABA signaling in promoting cotton fiber elongation and provide a strategy for improving cotton fiber quality.

Feasibility study of assessing cotton fiber maturity from near infrared hyperspectral imaging technique

Background Fiber maturity is a key cotton quality property,and its variability in a sample impacts fiber processing and dyeing performance.Currently,the maturity is determined by using established protocols in laboratories under a controlled environment.There is an increasing need to measure fiber maturity using low-cost(in general less than $20000)and small portable systems.In this study,a laboratory feasibility was performed to assess the ability of the shortwave infrared hyperspectral imaging(SWIR HSI)technique for determining the conditioned fiber maturity,and as a comparison,a bench-top commercial and expensive(in general greater than $60000)near infrared(NIR)instrument was used.Results Although SWIR HSI and NIR represent different measurement technologies,consistent spectral characteristics were observed between the two instruments when they were used to measure the maturity of the locule fiber samples in seed cotton and of the well-defined fiber samples,respectively.Partial least squares(PLS)models were established using different spectral preprocessing parameters to predict fiber maturity.The high prediction precision was observed by a lower root mean square error of prediction(RMSEP)(<0.046),higher R_(p)^(2)(>0.518),and greater percentage(97.0%)of samples within the 95% agreement range in the entire NIR region(1000-2500 nm)without the moisture band at 1940 nm.Conclusion SWIR HSI has a good potential for assessing cotton fiber maturity in a laboratory environment.

Deciphering the fiber quality of Gossypium barbadense L.var.brasiliensis in La Convención,Cusco,Perú

Background The quality of cotton fiber determines its value in the textile market,influencing agricultural profitability and the efficiency of textile processing.The selection of genotypes with superior fibers is a key factor for genetic improvement programs seeking adaptability and sustainability in the face of climate change.This demonstrates the strategic importance of this plant for sustainable agriculture and the global textile industry.The objective of this research was to decipher the fiber quality of Gossypium barbadense var.brasiliensis in the native Amazonian communities of La Convención,Cusco-Perú,and to evaluate other critical aspects of native cotton that have not yet been identified.The methodology included non-probability sampling for accessibility,qualitative and quantitative analyses,and multivariate analyses.The fiber length(mm),micronaire index(maturity/fineness),fiber strength(gf/tex),length uniformity index(%),fiber elongation(%),maturation index(%),and short fiber index(%)were the fiber characteristics evaluated using the HVI method in cotton genotypes.Results Cotton accessions collected from Koribeni(Gossypium spp.)and Shivankoreni(Gossypium barbadense var.brasiliensis)stood out for their fiber quality properties,especially length,strength,and uniformity,which highlights their relevance for advanced textile applications and potential for use in plant genetic improvement programs.Conclusion These findings reinforce the need to conserve and study these native cotton accessions from the Peruvian Amazon region,which can offer promising perspectives for the textile industry and agricultural biodiversity.

Alterations of Root and Fiber in Transgenic Cotton Plants with Chimeric Ph/P-ipt Gene Expression

The seed_specific phaseolin promoter (Ph/P) was fused to an ipt gene, then was cloned to a plant expression vector containing a gus gene driven by a 35S promoter. Cotton (Gossypium hirsutum L.) plants were transformed through pollen tube pathway methods. After seed germination, histochemical staining of the roots demonstrated that 32 GUS positive plants were obtained and three of which contained the chimeric Ph/P_ ipt transgene as confirmed by PCR analysis. An immunosorbent assay showed that two of the three transgenic cotton lines contained higher levels of zeatin equivalents in seeds than the control. Seedling development of these two transgenic lines differed from the control in a reduction of the shoot growth, showing a stunted phenotype as expected, but a surprisingly developed root system with a 3-4 fold fast_growing lateral roots. In addition, fibers (seed_hairs) of the two transgenic cotton lines were considerably shorter than those of the control. These results indicate that genetic engineering may be used to manipulate the development of cotton plants, particularly cotton fibers.

Comparison of Biochemical Substances in the Fiber Development of Different Cotton Varieties

Zhongmian 42 and Xinluzao 36 were used as raw materials to determine the contents of soluble sugar and protein, as well as dynamic changes of enzyme activities after flowering during cotton fiber growth. The results showed that contents of soluble protein in the two species sharply declined 7 to 21 days after flowering, as the soluble sugar in Zhongmian 42 leveling off after 21 days of flowering while the soluble sugar in Xinluzao 36 dropped notably after 21 days of flowering before remaining stable after seven days later. The soluble sugar decreased 7 to 14 days after flowering before sharply rising to the maximum seven days later, and then began to decline quickly. The soluble sugar was the minimum after 35 days of flowering and then remaining stable. Peroxidase activity generally increased. Indole-3- acetic acid oxidase activities were low at 7 days after flowering. IAAO activity reached to the peaks on the 14th and 28th day after flowering. IAAO activity of two varieties decreased with the same trend 35 days after flowering.

Effect of N fertilization rate on soil alkalihydrolyzable N, subtending leaf N concentration,fiber yield, and quality of cotton

Soil alkali-hydrolyzable nitrogen, which is sensitive to N fertilization rate, is one of the indicators of soil nitrogen supplying capacity. Two field experiments were conducted in Dongtai(120°19″ E, 32°52″ N), Jiangsu, China in 2009 and Dafeng(120°28″ E, 33°12″ N), Jiangsu province, China in 2010. Six nitrogen rates(0, 150, 300, 375, 450, and 600 kg ha^(-1)) were used to study the effect of N fertilization rate on soil alkali-hydrolyzable nitrogen content(SAHNC), subtending leaf nitrogen concentration(SLNC), yield, and fiber quality. In both Dongtai and Dafeng experiment station, the highest yield(1709 kg ha^(-1)), best quality(fiber length 30.6 mm, fiber strength 31.6 c N tex^(-1), micronaire 4.82), and highest N agronomic efficiency(2.03 kg kg^(-1)) were achieved at the nitrogen fertilization rate of 375 kg ha^(-1). The dynamics of SAHNC and SLNC could be simulated with a cubic and an exponential function,respectively. The changes in SAHNC were consistent with the changes in SLNC. Optimal average rate(0.276 mg day^(-1)) and duration(51.8 days) of SAHNC rapid decline were similar to the values obtained at the nitrogen rate of 375 kg ha^(-1)at which cotton showed highest fiber yield, quality, and N agronomic efficiency. Thus, the levels and strategies of nitrogen fertilization can affect SAHNC dynamics. The N fertilization rate that optimizes soil alkali-hydrolyzable nitrogen content would optimize the subtending leaf nitrogen concentration and thereby increase the yield and quality of the cotton fiber.

Gene expression and metabolite profiles of cotton fiber during cell elongation and secondary cell wall synthesis

Cotton fibers elongate rapidly after initiation of elongation, eventually leading to the deposit of a large amount of cellulose. To reveal features of cotton fiber cells at the fast elongation and the secondary cell wall synthesis stages, we compared the respective transcriptomes and metabolite profiles. Comparative analysis of transcriptomes by cDNA array identified 633 genes that were differentially regulated during fiber development. Principal component analysis （PCA） using expressed genes as variables divided fiber samples into four groups, which are diagnostic of developmental stages. Similar grouping results are also found if we use non-polar or polar metabolites as variables for PCA of developing fibers. Auxin signaling, wall-loosening and lipid metabolism are highly active during fiber elongation, whereas cellulose biosynthesis is predominant and many other metabolic pathways are downregulated at the secondary cell wall synthesis stage. Transcript and metabolite profiles and enzyme activities are consistent in demonstrating a specialization process of cotton fiber development toward cellulose synthesis. These data demonstrate that cotton fiber cell at a certain stage has its own unique feature, and developmental stages of cotton fiber cells can be distinguished by their transcript and metabolite profiles. During the secondary cell wall synthesis stage, metabolic pathways are streamed into cellulose synthesis.

Ameliorative effects of potassium on drought-induced decreases in fiber length of cotton(Gossypium hirsutum L.) are associated with osmolyte dynamics during fiber development

Fiber length of cotton(Gossypium hirsutum L.)decreases under drought stress,potassium(K)could diminish the decreased caused by drought,but the mechanism associated with this alleviation effect is not clear.We evaluated the effect of K on fiber elongation using two cotton cultivars,Simian 3 and Siza 3,grown in well-watered and drought-stressed conditions.Potassium fertilizer(K2O)was applied 0,150,or 300 kg ha?1 in each growing condition.Drought stress reduced the final fiber length due to a decline in the maximum rate of rapid elongation(Vmax,mmday?1).The application of K alleviated the droughtinduced fiber length reduction by increasing Vmax.At 10 and 15 days post-anthesis(DPA),drought significantly reduced osmotic potential(OP)and increased K+and malate contents at all K rates,relative to well-watered conditions,which was associated with increased activities of phosphoenolpyruvate carboxylase(PEPC),V-ATPase,PPase,and PM H+-ATPase in cotton fiber.However,the relative contribution of K+and malate to OP declined under drought in comparison with well-watered condition.Compared with control without K,K application decreased OP and increased the accumulation of osmolytes(K+,malate and soluble sugar)as well as the activities of related enzymes in fiber irrespective of water treatments.Moreover,K application increased osmotic adjustment during drought,and improved the contribution of K+and malate to OP,especially under drought stress.This study showed that drought decreased fiber length by reducing Vmax,and K application ameliorates the decline in fiber elongation due to drought by enhancing osmolytes accumulation and their contribution to OP in fiber cells.