Secondary Cell Wall Research Articles

Dielectric barrier discharge plasma delayed the textural hardening of bamboo shoots by regulating cell wall metabolism

Postharvest bamboo shoots may undergo a hardening process even under low-temperature storage. Dielectric barrier discharge plasma (DBDP) is a promising non-thermal preservation technology, which reportedly delays senescence and improves the texture of plants. The influences of DBDP treatment on the changes of quality attributes, cell wall components, and cell wall modifying enzymes in Lei bamboo (Phyllostachys praecox) shoots were investigated. DBDP treatment improved the shelf life, texture, and energy level while decreasing the cell membrane permeability, malondialdehyde content, and hydrogen peroxide contents of bamboo shoots. DBDP treatment obtained a higher ratio of water-soluble pectin to CDTA-soluble pectin contents as well as lower levels of cellulose and hemicellulose contents by regulating the cell wall modifying enzymes, inhibiting the self-assembly of pectin gels and cellulose-xyloglucan networks. Scanning and transmission electron microscopy showed that DBDP treatment slightly destabilized the cell wall and inhibited secondary cell wall formation. The results showed that DBDP treatment inhibited the hardening process and maintained a better texture of bamboo shoots under low-temperature storage.

A group III patatin-like phospholipase gene pPLAIIIδ regulates lignin biosynthesis and influences the rate of seed germination in Arabidopsis thaliana.

The lignification of plant secondary walls is an important process that provides plants with mechanical support. However, the presence of lignin in the secondary walls affects the readily availability of cellulose required in various industries, including the biofuel, paper, and textile industries. Thus, plants with less lignin are ideal for usage in such industries. Molecular studies have identified genes that regulate plant lignification, including group III plant-specific patatin-related phospholipase genes. Recent studies have reported decreased lignin content when pPLAIIIα, pPLAIIIγ (from Arabidopsis thaliana), and pPLAIIIβ (from Panax ginseng) were overexpressed in Arabidopsis. However, the role played by a closely related gene pPLAIIIδ in lignin biosynthesis has not yet been reported. In this study, we found that overexpression of the pPLAIIIδ significantly reduced the lignin content in secondary cell walls, whereas the silencing of the gene increased secondary walls lignification. Transcript level analysis showed that the key structural and regulatory genes involved in the lignin biosynthesis pathway decreased in overexpression, and increased in plants with silenced pPLAIIIδ. Further analysis revealed that pPLAIIIδ played an influential role in several physiological processes including seed germination, and chlorophyll accumulation. Moreover, the gene also influenced the size of plants and plant organs, including leaves, seeds, and root hairs. Generally, our study provides important insights toward the use of genetic engineering for lignin reduction in plants and provides information about the agronomical and physiological suitability of pPLAIIIδ transgenic plants for utilization in biomass processing industries.

High temperature inhibits vascular development via the PIF4-miR166-HB15 module in Arabidopsis

The plant vascular system is an elaborate network of conducting and supporting tissues that extends throughout the plant body, and its structure and function must be orchestrated with different environmental conditions. Under high temperature, plants display thin and lodging stems that may lead to decreased yield and quality of crops. However, the molecular mechanism underlying high-temperature-mediated regulation of vascular development is not known. Here, we show that Arabidopsis plants overexpressing the basic-helix-loop-helix (bHLH) transcription factor PHYTOCHROME INTERACTING FACTOR 4 (PIF4), a central regulator of high-temperature signaling, display fewer vascular bundles (VBs) and decreased secondary cell wall (SCW) thickening, mimicking the lodging inflorescence stems of high-temperature-grown wild-type plants. Rising temperature and elevated PIF4 expression reduced the expression of MIR166 and, concomitantly, elevated the expression of the downstream class III homeodomain leucine-zipper (HD-ZIP III) family gene HB15. Consistently, knockdown of miR166 and overexpression of HB15 led to inhibition of vascular development and SCW formation, whereas the hb15 mutant displayed the opposite phenotype in response to high temperature. Moreover, invitro and invivo assays verified that PIF4 binds to the promoters of several MIR166 genes and represses their expression. Our study establishes a direct functional link between PIF4 and the miR166-HB15 module in modulating vascular development and SCW thickening and consequently stem-lodging susceptibility at elevated temperatures.

Genome-Wide Identification, Expansion, Evolution, and Expression Analysis Reveals ABCB Genes Important for Secondary Cell Wall Development in Moso Bamboo (Phyllostachys edulis)

The ATP-binding cassette subfamily B (ABCB) is an important transporter family, and many members are well known for their auxin transport function. However, reports on the function of the ABCB genes during Moso bamboo development are few. In this study, we identified and characterized 37 PhABCB genes in Moso bamboo and classified them into five subgroups, Ⅰ–Ⅴ. We further observed gene family expansion and gene loss events during the evolution of the PhABCB gene family. It was found that the expansion of the PhABCB family was mainly attributed to the whole-genome duplication and DNA-transposed duplication models. Gene co-expression analysis and quantitative real-time PCR revealed that several PhABCB genes may be involved in the development of the secondary cell wall (SCW) during the rapid growth of Moso bamboo. Through examining their expression in different parts of the bamboo internode where the cell walls exhibited different developmental stages, the roles of eight candidate PhABCBs in the SCW development were further characterized. Of the eight PhABCB genes, PhABCB7, PhABCB11, PhABCB14, and PhABCB21 may be involved in the SCW biogenesis in Moso bamboo. This study provides the basis for discovering the potential role of PhABCB genes in Moso bamboo cell wall development; further studies are needed to elucidate how these PhABCBs function in SCW development by regulating the polar transport of auxin.

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.

MicroRNA397 regulates tolerance to drought and fungal infection by regulating lignin deposition in chickpea root.

Plants deposit lignin in the secondary cell wall as a common response to drought and pathogen attacks. Cell wall localised multicopper oxidase family enzymes LACCASES (LACs) catalyse the formation of monolignol radicals and facilitate lignin formation. We show an upregulation of the expression of several LAC genes and a downregulation of microRNA397 (CamiR397) in response to natural drought in chickpea roots. CamiR397 was found to target LAC4 and LAC17L out of twenty annotated LACs in chickpea. CamiR397 and its target genes are expressed in the root. Overexpression of CamiR397 reduced expression of LAC4 and LAC17L and lignin deposition in chickpea root xylem causing reduction in xylem wall thickness. Downregulation of CamiR397 activity by expressing a short tandem target mimic (STTM397) construct increased root lignin deposition in chickpea. CamiR397-overexpressing and STTM397 chickpea lines showed sensitivity and tolerance, respectively, towards natural drought. Infection with a fungal pathogen Macrophomina phaseolina, responsible for dry root rot (DRR) disease in chickpea, induced local lignin deposition and LAC gene expression. CamiR397-overexpressing and STTM397 chickpea lines showed more sensitivity and tolerance, respectively, to DRR. Our results demonstrated the regulatory role of CamiR397 in root lignification during drought and DRR in an agriculturally important crop chickpea.

The genome of the glasshouse plant noble rhubarb (Rheum nobile) provides a window into alpine adaptation

Glasshouse plants are species that trap warmth via specialized morphology and physiology, mimicking a human glasshouse. In the Himalayan alpine region, the highly specialized glasshouse morphology has independently evolved in distinct lineages to adapt to intensive UV radiation and low temperature. Here we demonstrate that the glasshouse structure – specialized cauline leaves – is highly effective in absorbing UV light but transmitting visible and infrared light, creating an optimal microclimate for the development of reproductive organs. We reveal that this glasshouse syndrome has evolved at least three times independently in the rhubarb genus Rheum. We report the genome sequence of the flagship glasshouse plant Rheum nobile and identify key genetic network modules in association with the morphological transition to specialized glasshouse leaves, including active secondary cell wall biogenesis, upregulated cuticular cutin biosynthesis, and suppression of photosynthesis and terpenoid biosynthesis. The distinct cell wall organization and cuticle development might be important for the specialized optical property of glasshouse leaves. We also find that the expansion of LTRs has likely played an important role in noble rhubarb adaptation to high elevation environments. Our study will enable additional comparative analyses to identify the genetic basis underlying the convergent occurrence of glasshouse syndrome.

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.

Impact of hemicelluloses and crystal size on X-ray scattering from atomistic models of cellulose microfibrils

X-ray scattering methods allow efficient characterization of cellulosic materials, but interpreting their results is challenging. By creating molecular dynamics models of cellulose microfibrils and calculating the scattering from them, we investigated how different properties of the structures affect their scattering intensities. We studied the effects of hemicelluloses and crystal size on small-angle and wide-angle X-ray scattering (SAXS, WAXS). Microfibril models with and without surface-bound hemicelluloses were built based on the chemical composition of spruce secondary cell walls. The effect of fibril size was investigated by comparing the scattering from fibrils with 14 to 40 cellulose chains. The hemicelluloses appeared in the SAXS region as an increase in the fibril radius and as a clear contribution of a shell around the fibril. The hemicelluloses also increased the crystal size as determined from the broadening of the 200 diffraction peak of cellulose textrm{I}_upbeta. The SAXS and WAXS analysis provided consistent estimates for the size of the microfibrils, and their special features and challenges were discussed. In particular, the results of 18-chain microfibrils were consistent with prior experimental results. Carrying out the simulations in wet and dry environments had the most pronounced effect on fibrils with a hemicellulose coating. Twisting of the fibril had very little impact on most properties, except for a minor effect on the WAXS peaks. The results allow for more correct interpretation of experimental scattering results, leading to more accurate descriptions of microfibril structures in natural and processed cellulosic materials.

Two R2R3-MYB transcription factors from Chinese cedar (Cryptomeria fortunei Hooibrenk) are involved in the regulation of secondary cell wall formation

As the most abundant renewable energy source, wood comprises the secondary cell wall (SCW). SCW biosynthesis involves lignin and cellulose deposition. Increasing studies have illustrated that R2R3-MYB transcription factors (TFs) play pivotal roles in affecting lignin accumulation and SCW formation. Nevertheless, the regulatory roles of R2R3-MYBs are still unresolved in Cryptomeria fortunei Hooibrenk cambium and wood formation. To dissect the potentials of CfMYBs, we successfully cloned and intensively studied the functions of CfMYB4 and CfMYB5 in SCW formation and abiotic stress response. They both contained the conserved MYB domain capable of forming a special structure that could bind to the core motifs of downstream genes. The phylogenetic tree implied that two CfMYBs clustered into different evolutionary branches. They were predominantly expressed in the stem and were localized to the nucleus. Furthermore, CfMYB4 functioned as an activator to enhance lignin and cellulose accumulation, and increase the SCW thickness by elevating the expression levels of SCW-related genes. By contrast, CfMYB5 negatively regulated lignin and cellulose biosynthesis, and decreased SCW formation by reducing the expression of SCW biosynthetic genes. Our data not only highlight the regulatory functions of CfMYBs in lignin deposition but also provide critical insights into the development of strategies for the genetic improvement of Cryptomeria fortunei wood biomass.

IQ domain-containing protein ZmIQD27 modulates water transport in maize.

Plant metaxylem vessels provide physical support to promote upright growth and the transport of water and nutrients. A detailed characterization of the molecular network controlling metaxylem development is lacking. However, knowledge of the events that regulate metaxylem development could contribute to the development of germplasm with improved yield. In this paper, we screened an ethyl methane sulfonate (EMS)-induced B73 mutant library, which covers 92% of maize (Zea mays) genes, to identify drought-sensitive phenotypes. Three mutants were identified, named iqd27-1, iqd27-2, and iqd27-3, and genetic crosses showed that they were allelic to each other. The causal gene in these three mutants encodes the IQ domain-containing protein ZmIQD27. Our study showed that defective metaxylem vessel development likely causes the drought sensitivity and abnormal water transport phenotypes in the iqd27 mutants. ZmIQD27 was expressed in the root meristematic zone where secondary cell wall deposition is initiated, and loss-of-function iqd27 mutants exhibited a microtubular arrangement disorder. We propose that association of functional ZmIQD27 with microtubules is essential for correct targeted deposition of the building blocks for secondary cell wall development in maize.

Forces on and in the cell walls of living plants.

Environmental influences and differential growth subject plants to mechanical forces. Forces on the whole plant resolve into tensile forces on its primary cell walls and both tensile and compression forces on the secondary cell wall layers of woody tissues. Forces on cell walls are further resolved into forces on cellulose microfibrils and the noncellulosic polymers between them. Many external forces on plants oscillate, with time constants that vary from seconds to milliseconds. Sound waves are a high-frequency example. Forces on the cell wall lead to responses that direct the oriented deposition of cellulose microfibrils and the patterned expansion of the cell wall, leading to complex cell and tissue morphology. Recent experiments have established many of the details of which cell wall polymers associate with one another in both primary and secondary cell walls, but questions remain about which of the interconnections are load bearing, especially in primary cell walls. Direct cellulose-cellulose interactions appear to have a more important mechanical role than was previously thought, and some of the noncellulosic polymers may have a role in keeping microfibrils apart rather than cross-linking them as formerly envisaged.

Transcriptome features of stone cell development in weevil-resistant and susceptible Sitka spruce.

Stone cells are a specialized, highly lignified cell type found in both angiosperms and gymnosperms. In conifers, abundance of stone cells in the cortex provides a robust constitutive physical defense against stem feeding insects. Stone cells are a major insect-resistance trait in Sitka spruce (Picea sitchensis), occurring in dense clusters in apical shoots of trees resistant (R) to spruce weevil (Pissodes strobi) but being rare in susceptible (S) trees. To learn more about molecular mechanisms of stone cell formation in conifers, we used laser microdissection and RNA sequencing to develop cell-type-specific transcriptomes of developing stone cells from R and S trees. Using light, immunohistochemical, and fluorescence microscopy, we also visualized the deposition of cellulose, xylan, and lignin associated with stone cell development. A total of 1293 genes were differentially expressed at higher levels in developing stone cells relative to cortical parenchyma. Genes with potential roles in stone cell secondary cell wall formation (SCW) were identified and their expression evaluated over a time course of stone cell formation in R and S trees. The expression of several transcriptional regulators was associated with stone cell formation, including a NAC family transcription factor and several genes annotated as MYB transcription factors with known roles in SCW formation.

Overexpression of REDUCED WALL ACETYLATION C increases xylan acetylation and biomass recalcitrance in Populus.

Plant lignocellulosic biomass, i.e. secondary cell walls of plants, is a vital alternative source for bioenergy. However, the acetylation of xylan in secondary cell walls impedes the conversion of biomass to biofuels. Previous studies have shown that REDUCED WALL ACETYLATION (RWA) proteins are directly involved in the acetylation of xylan but the regulatory mechanism of RWAs is not fully understood. In this study, we demonstrate that overexpression of a Populus trichocarpa PtRWA-C gene increases the level of xylan acetylation and increases the lignin content and S/G ratio, ultimately yielding poplar woody biomass with reduced saccharification efficiency. Furthermore, through gene coexpression network and expression quantitative trait loci (eQTL) analysis, we found that PtRWA-C was regulated not only by the secondary cell wall hierarchical regulatory network but also by an AP2 family transcription factor HARDY (HRD). Specifically, HRD activates PtRWA-C expression by directly binding to the PtRWA-C promoter, which is also the cis-eQTL for PtRWA-C. Taken together, our findings provide insights into the functional roles of PtRWA-C in xylan acetylation and consequently saccharification and shed light on synthetic biology approaches to manipulate this gene and alter cell wall properties. These findings have substantial implications for genetic engineering of woody species, which could be used as a sustainable source of biofuels, valuable biochemicals, and biomaterials.

Characterization of chromatin accessibility and gene expression reveal the key genes involved in cotton fiber elongation.

Cotton (Gossypium hirsutum L.) is an important economic crop, and cotton fiber is one of the longest plant cells, which provides an ideal model for the study of cell elongation and secondary cell wall synthesis. Cotton fiber length is regulated by a variety of transcription factors (TF) and their target genes; however, the mechanism of fiber elongation mediated by transcriptional regulatory networks is still unclear to a large extent. Here, we used a comparative assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) assay and RNA-seq analysis to identify fiber elongation transcription factors and genes using the short-fiber mutant ligon linless-2 (Li2 ) and wild type (WT). A total of 499 differential target genes were identified and GO analysis shows that differential genes are mainly involved in plant secondary wall synthesis and microtubule-binding processes. Analysis of the genomic regions preferentially accessible (Peak) has identified a number of overrepresented TF-binding motifs, highlighting sets of TFs that are important for cotton fiber development. Using ATAC-seq and RNA-seq data, we have constructed a functional regulatory network of each TF regulatory target gene and also the network pattern of TF regulating differential target genes. Further, to obtain the genes related to fiber length, the differential target genes were combined with FLGWAS data to identify the genes highly related to fiber length. Our work provides new insights into cotton fiber elongation.

A Pectate Lyase Gene Plays a Critical Role in Xylem Vascular Development in Arabidopsis.

As a major component of the plant primary cell wall, structure changes in pectin may affect the formation of the secondary cell wall and lead to serious consequences on plant growth and development. Pectin-modifying enzymes including pectate lyase-like proteins (PLLs) participate in the remodeling of pectin during organogenesis, especially during fruit ripening. In this study, we used Arabidopsis as a model system to identify critical PLL genes that are of particular importance for vascular development. Four PLL genes, named AtPLL15, AtPLL16, AtPLL19, and AtPLL26, were identified for xylem-specific expression. A knock-out T-DNA mutant of AtPLL16 displayed an increased amount of pectin, soluble sugar, and acid-soluble lignin (ASL). Interestingly, the atpll16 mutant exhibited an irregular xylem phenotype, accompanied by disordered xylem ray cells and an absence of interfascicular phloem fibers. The xylem fiber cell walls in the atpll16 mutant were thicker than those of the wild type. On the contrary, AtPLL16 overexpression resulted in expansion of the phloem and a dramatic change in the xylem-to-phloem ratios. Altogether, our data suggest that AtPLL16 as a pectate lyase plays an important role during vascular development in Arabidopsis.

The OsbHLH002/OsICE1-OSH1 module orchestrates secondary cell wall formation in rice

Transcriptional regulation of secondary cell wall (SCW) formation is strictly controlled by a complex network of transcription factors in vascular plants and has been shown to be mediated by a group of NAC master switches. In this study, we show that in a bHLH transcription factor, OsbHLH002/OsICE1, its loss-of-function mutant displays a lodging phenotype. Further results show that OsbHLH002 and Oryza sativa homeobox1 (OSH1) interact and share a set of common targets. In addition, the DELLA protein SLENDER RICE1, rice ortholog of KNOTTED ARABIDOPSIS THALIANA7, and OsNAC31 interact with OsbHLH002 and OSH1 and regulate their binding capacity on OsMYB61, a key regulatory factor in SCW development. Collectively, our results indicate OsbHLH002 and OSH1 as key regulators in SCW formation and shed light on molecular mechanisms of how active and repressive factors precisely orchestrate SCW synthesis in rice, which may provide a strategy for manipulating plant biomass production.

Rice-Magnaporthe transcriptomics reveals host defense activation induced by red seaweed-biostimulant in rice plants.

Red seaweed extracts have been shown to trigger the biotic stress tolerance in several crops. However, reports on transcriptional modifications in plants treated with seaweed biostimulant are limited. To understand the specific response of rice to blast disease in seaweed-biostimulant-primed and non-primed plants, transcriptomics of a susceptible rice cultivar IR-64 was carried out at zero and 48h post inoculation with Magnaporthe oryzae (strain MG-01). A total of 3498 differentially expressed genes (DEGs) were identified; 1116 DEGs were explicitly regulated in pathogen-inoculated treatments. Functional analysis showed that most DEGs were involved in metabolism, transport, signaling, and defense. In a glass house, artificial inoculation of MG-01 on seaweed-primed plants resulted in the restricted spread of the pathogen leading to the confined blast disease lesions, primarily attributed to reactive oxygen species (ROS) accumulation. The DEGs in the primed plants were defense-related transcription factors, kinases, pathogenesis-related genes, peroxidases, and growth-related genes. The beta-D-xylosidase, a putative gene that helps in secondary cell wall reinforcement, was downregulated in non-primed plants, whereas it upregulated in the primed plants indicating its role in the host defense. Additionally, Phenylalanine ammonia-lyase, pathogenesis-related Bet-v-I family protein, chalcone synthase, chitinases, WRKY, AP2/ERF, and MYB families were upregulated in seaweed and challenge inoculated rice plants. Thus, our study shows that priming rice plants with seaweed bio-stimulants resulted in the induction of the defense in rice against blast disease. This phenomenon is contributed to early protection through ROS, protein kinase, accumulation of secondary metabolites, and cell wall strengthening.

Root and Leaf Anatomy, Ion Accumulation, and Transcriptome Pattern under Salt Stress Conditions in Contrasting Genotypes of Sorghum bicolor.

Roots from salt-susceptible ICSR-56 (SS) sorghum plants display metaxylem elements with thin cell walls and large diameter. On the other hand, roots with thick, lignified cell walls in the hypodermis and endodermis were noticed in salt-tolerant CSV-15 (ST) sorghum plants. The secondary wall thickness and number of lignified cells in the hypodermis have increased with the treatment of sodium chloride stress to the plants (STN). Lignin distribution in the secondary cell wall of sclerenchymatous cells beneath the lower epidermis was higher in ST leaves compared to the SS genotype. Casparian thickenings with homogenous lignin distribution were observed in STN roots, but inhomogeneous distribution was evident in SS seedlings treated with sodium chloride (SSN). Higher accumulation of K+ and lower Na+ levels were noticed in ST compared to the SS genotype. To identify the differentially expressed genes among SS and ST genotypes, transcriptomic analysis was carried out. Both the genotypes were exposed to 200 mM sodium chloride stress for 24 h and used for analysis. We obtained 70 and 162 differentially expressed genes (DEGs) exclusive to SS and SSN and 112 and 26 DEGs exclusive to ST and STN, respectively. Kyoto Encyclopaedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analysis unlocked the changes in metabolic pathways in response to salt stress. qRT-PCR was performed to validate 20 DEGs in each SSN and STN sample, which confirms the transcriptomic results. These results surmise that anatomical changes and higher K+/Na+ ratios are essential for mitigating salt stress in sorghum apart from the genes that are differentially up- and downregulated in contrasting genotypes.

Bnt05G007257, a Novel NAC Transcription Factor, Predicts Developmental and Synthesis Capabilities of Fiber Cells in Ramie (Boehmeria nivea L.)

NAC transcription factors are one of the largest transcription factor families in plants, and they play a key role in the growth and development of a secondary cell wall. Despite the fact that ramie is well-known for its high fiber yield, the role of NAC transcription factors in ramie secondary cell wall synthesis and fiber development remains unknown. In this study, based on our previous study, we describe the characterization, physicochemical property analysis, protein structure and function prediction, subcellular localization, and functional validation of Bnt05G007257, which encodes an NAC transcription factor from ramie, in transgenic A. thaliana. Our findings show that the open reading frame of Bnt05G007257 was 1035 bp long and encodes for a protein comprising 344 amino acids, having a relative molecular mass of 39.0945 kDa and a theoretical isoelectric point of 6.55. The secondary structure of the encoded protein mainly consisted of random coiling, with a typical conserved structural domain of NAC. The phylogenetic tree revealed that Bnt05G007257 is a homolog of the NAC transcription factor SND2, which regulates secondary wall biosynthesis in A. thaliana. Subcellular localization showed that Bnt05G007257 was tentatively predicted to be localized in the cytoplasm. Furthermore, in stem sections, the secondary wall fiber cells’ thickness in Bnt05G007257 transgenic plants was 31.50% thicker than that in wild-type plants, and the radial width was significantly increased by approximately 21.75%. This indicates that the NAC family homolog Bnt05G007257 may have the potential function of promoting fiber cell development and secondary cell wall synthesis, providing a theoretical basis for the selection of high-fiber-yielding ramie varieties in the future.