Lignin Biosynthetic Pathway Research Articles

A Molecular Blueprint of Lignin Repression.

Although lignin is essential to ensure the correct growth and development of land plants, it may be an obstacle to the production of lignocellulosics-based biofuels, and reduces the nutritional quality of crops used for human consumption or livestock feed. The need to tailor the lignocellulosic biomass for more efficient biofuel production or for improved plant digestibility has fostered considerable advances in our understanding of the lignin biosynthetic pathway and its regulation. Most of the described regulators are transcriptional activators of lignin biosynthesis, but considerably less attention has been devoted to the repressors of this pathway. We provide a comprehensive overview of the molecular factors that negatively impact on the lignification process at both the transcriptional and post-transcriptional levels.

R2R3-MYB transcription factor MYB6 promotes anthocyanin and proanthocyanidin biosynthesis but inhibits secondary cell wall formation in Populus tomentosa.

The secondary cell wall is an important carbon sink in higher plants and its biosynthesis requires coordination of metabolic fluxes in the phenylpropanoid pathway. In Arabidopsis (Arabidopsis thaliana), MYB75 and the KNOX transcription factor KNAT7 form functional complexes to regulate secondary cell wall formation in the inflorescence stem. However, the molecular mechanism by which these transcription factors control different branches of the phenylpropanoid pathway remains poorly understood in woody species. We isolated an R2R3-MYB transcription factor MYB6 from Populus tomentosa and determined that it was expressed predominately in young leaves. Overexpression of MYB6 in transgenic poplar upregulated flavonoid biosynthetic gene expression, resulting in significantly increased accumulation of anthocyanin and proanthocyanidins. MYB6-overexpression plants showed reduced secondary cell wall deposition, accompanied by repressed expression of secondary cell wall biosynthetic genes. We further showed that MYB6 interacted physically with KNAT7 and formed functional complexes that acted to repress secondary cell wall development in poplar and Arabidopsis. The results provide an insight into the transcriptional mechanisms involved in the regulation of the metabolic fluxes between the flavonoid and lignin biosynthetic pathways in poplar.

Imaging Changes in Cell Walls of Engineered Poplar by Stimulated Raman Scattering and Atomic Force Microscopy

Lignin is a major impediment in the deconstruction of plant biomass to its soluble monomeric constituents. Modification of the lignin biosynthetic pathway has proven to be an effective means of red...

Low Lignin Mutants and Reduction of Lignin Content in Grasses for Increased Utilisation of Lignocellulose

Biomass rich in lignocellulose from grasses is a major source for biofuel production and animal feed. However, the presence of lignin in cell walls limits its efficient utilisation such as in its bioconversion to biofuel. Reduction of the lignin content or alteration of its structure in crop plants have been pursued, either by regulating genes encoding enzymes in the lignin biosynthetic pathway using biotechnological techniques or by breeding naturally-occurring low lignin mutant lines. The aim of this review is to provide a summary of these studies, focusing on lignin (monolignol) biosynthesis and composition in grasses and, where possible, the impact on recalcitrance to bioconversion. An overview of transgenic crops of the grass family with regulated gene expression in lignin biosynthesis is presented, including the effect on lignin content and changes in the ratio of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units. Furthermore, a survey is provided of low-lignin mutants in grasses, including cereals in particular, summarising their origin and phenotypic traits together with genetics and the molecular function of the various genes identified.

Combining loss of function of FOLYLPOLYGLUTAMATE SYNTHETASE1 and CAFFEOYL-COA 3-O-METHYLTRANSFERASE1 for lignin reduction and improved saccharification efficiency in Arabidopsis thaliana

BackgroundDownregulation of genes involved in lignin biosynthesis and related biochemical pathways has been used as a strategy to improve biofuel production. Plant C1 metabolism provides the methyl units used for the methylation reactions carried out by two methyltransferases in the lignin biosynthetic pathway: caffeic acid 3-O-methyltransferase (COMT) and caffeoyl-CoA 3-O-methyltransferase (CCoAOMT). Mutations in these genes resulted in lower lignin levels and altered lignin compositions. Reduced lignin levels can also be achieved by mutations in the C1 pathway gene, folylpolyglutamate synthetase1 (FPGS1), in both monocotyledons and dicotyledons, indicating a link between the C1 and lignin biosynthetic pathways. To test if lignin content can be further reduced by combining genetic mutations in C1 metabolism and the lignin biosynthetic pathway, fpgs1ccoaomt1 double mutants were generated and functionally characterized.ResultsDouble fpgs1ccoaomt1 mutants had lower thioacidolysis lignin monomer yield and acetyl bromide lignin content than the ccoaomt1 or fpgs1 mutants and the plants themselves displayed no obvious long-term negative growth phenotypes. Moreover, extracts from the double mutants had dramatically improved enzymatic polysaccharide hydrolysis efficiencies than the single mutants: 15.1% and 20.7% higher than ccoaomt1 and fpgs1, respectively. The reduced lignin and improved sugar release of fpgs1ccoaomt1 was coupled with changes in cell-wall composition, metabolite profiles, and changes in expression of genes involved in cell-wall and lignin biosynthesis.ConclusionOur observations demonstrate that additional reduction in lignin content and improved sugar release can be achieved by simultaneous downregulation of a gene in the C1 (FPGS1) and lignin biosynthetic (CCOAOMT) pathways. These improvements in sugar accessibility were achieved without introducing unwanted long-term plant growth and developmental defects.

The soybean cinnamate 4-hydroxylase gene GmC4H1 contributes positively to plant defense via increasing lignin content

Lignification is a key event in plant defense against pathogens. In the plant lignin biosynthetic pathway, cinnamate 4-hydroxylase (C4H) catalyzes the conversion of trans-cinnamic acid to p-coumaric acid. However, the potential role of C4H in plant defense remains elusive. In this research, a soybean C4H gene, GmC4H1, was identified via microarray-based comparative transcriptome analysis of genes responsive to Phytophthora sojae infection. The accumulation of GmC4H1 transcripts increased significantly upon P. sojae infection. Nicotiana benthamiana plants overexpressing GmC4H1 demonstrated enhanced lignin accumulation and elevated resistance to both Phytophthora parasitica and Verticillium dahliae. The silencing of GmC4H1 in soybean hairy roots resulted in decreased resistance to P. sojae. These results together suggest that GmC4H1 contributes positively to plant defense against various pathogens, possibly by enhancing lignin biosynthesis.

Transcriptome analysis provides insights into the regulation of metabolic processes during postharvest cold storage of loquat (Eriobotrya japonica) fruit

Loquat (Eriobotrya japonica) fruit accumulates lignin during postharvest storage under chilling conditions (0 °C), while low-temperature conditioning (LTC; 5 °C for 6 days followed by transfer to 0 °C) or heat treatment (HT; 40 °C for 4 h followed by transfer to 0 °C) can alleviate lignification. Here we compared transcriptome profiles of loquat fruit samples under LTC or HT to those stored at 0 °C at five time points from day 1 to day 8 after treatment. High-throughput transcriptome sequences were de novo assembled into 53,319 unique transcripts with an N50 length of 1306 bp. A total of 2235 differentially expressed genes were identified in LTC, and 1020 were identified in HT compared to 0 °C. Key genes in the lignin biosynthetic pathway, including EjPAL2, EjCAD1, EjCAD3, 4CL, COMT, and HCT, were responsive to LTC or HT treatment, but they showed different expression patterns during the treatments, indicating that different structural genes could regulate lignification at different treatment stages. Coexpression network analysis showed that these candidate biosynthetic genes were associated with a number of transcription factors, including those belonging to the AP2, MYB, and NAC families. Gene ontology (GO) enrichment analysis of differentially expressed genes indicated that biological processes such as stress responses, cell wall and lignin metabolism, hormone metabolism, and metal ion transport were significantly affected under LTC or HT treatment when compared to 0 °C. Our analyses provide insights into transcriptome responses to postharvest treatments in loquat fruit.

Overexpression of cinnamyl alcohol dehydrogenase gene from sweetpotato enhances oxidative stress tolerance in transgenic Arabidopsis

Cinnamyl alcohol dehydrogenase (CAD) is the enzyme in the last step of lignin biosynthetic pathway and is involved in the generation of lignin monomers. IbCAD1 gene in sweetpotato (Ipomoea batatas) was identified, and its expression was induced by abiotic stresses based on promoter analysis. In this study, transgenic Arabidopsis plants overexpressing IbCAD1 directed by CaMV 35S promoter were developed to determine the physiological function of IbCAD1. IbCAD1-overexpressing transgenic plants exhibited better plant growth and higher biomass compared to wild type (WT), under normal growth conditions. CAD activity was increased in leaves and roots of transgenic plants. Sinapyl alcohol dehydrogenase activity was induced to a high level in roots, which suggests that IbCAD1 may regulate biosynthesis of syringyl-type (S) lignin. Lignin content was increased in stems and roots of transgenic plants; this increase was in S lignin rather than guaiacyl (G) lignin. Overexpression of IbCAD1 in Arabidopsis resulted in enhanced seed germination rates and tolerance to reactive oxygen species (ROS), such as hydrogen peroxide (H2O2). Taken together, our results show that IbCAD1 controls lignin content by biosynthesizing S units and plays an important role in plant responses to oxidative stress.

Ectopic Expression of PtoMYB74 in Poplar and Arabidopsis Promotes Secondary Cell Wall Formation.

In vascular plants, R2R3-MYB transcription factors are important regulators of secondary cell wall formation. Although 192 annotated R2R3 MYB genes were identified in the poplar genome, only a few members were characterized to participate in the regulation of the secondary cell wall biosynthesis. In this paper, we identify an R2R3-MYB transcription factor, PtoMYB74, which is predicted to be an ortholog of Arabidopsis AtMYB61, a transcription activator that regulates the secondary cell wall formation, lignin biosynthesis, stomatal aperture, and the mucilage of seed coat. PtoMYB74 is mainly expressed in the stems, especially in the xylem tissues and organs. PtoMYB74 as a transcriptional activator is localized to the nucleus. The overexpression of PtoMYB74 increased the secondary cell wall thickness of vessels in transgenic poplar and changed the secondary cell wall compositions. The expression levels of lignin and cellulose biosynthetic genes were elevated in the transgenic poplar overexpressing PtoMYB74 compared to the wild type, while there was no change in the xylan biosynthetic genes. Transcriptional activation assays demonstrated that PtoMYB74 could activate the promoters of structural genes in the lignin and cellulose biosynthetic pathways. Taken together, our data show that PtoMYB74 positively regulates the secondary cell wall biosynthesis in poplar.

Trichoderma mediate early and enhanced lignifications in chickpea during Fusarium oxysporum f. sp. ciceris infection.

Lignifications in secondary cell walls play a significant role in defense mechanisms of plants against the invading pathogens. In the present study, we investigated Trichoderma strain specific lignifications in chickpea plants pre-treated with 10 potential Trichoderma strains and subsequently challenged with the wilt pathogen Fusarium oxysporum f. sp. ciceris (Foc). Trichoderma-induced lignifications in chickpea were observed through histochemical staining and expression of some genes of the lignin biosynthetic pathway. Lignifications were observed in transverse sections of shoots near the soil line through histochemical staining and expression pattern of the target genes was observed in root tissues through semi quantitative RT-PCR at different time intervals after inoculation of F. oxysporum f. sp. ciceris. Lignin deposition and expression pattern of the target genes were variable in each treatment. Lignifications were enhanced in all 10 Trichoderma strain treated and F. oxysporum f. sp. ciceris challenged chickpea plants. However, four Trichoderma strains viz., T-42, MV-41, DFL, and RO, triggered significantly high lignifications compared to the other six strains. Time course studies showed that effective Trichoderma isolates induced lignifications very early compared to the other strains and the process of lignifications nearly completes within 6 days of pathogen challenge. Thus, from the results it can be concluded that effective Trichoderma strains trigger lignifications very early in chickpea under Foc challenge and provide better protection to chickpea plants.

A dynamic model of lignin biosynthesis in Brachypodium distachyon

BackgroundLignin is a crucial molecule for terrestrial plants, as it offers structural support and permits the transport of water over long distances. The hardness of lignin reduces plant digestibility by cattle and sheep; it also makes inedible plant materials recalcitrant toward the enzymatic fermentation of cellulose, which is a potentially valuable substrate for sustainable biofuels. Targeted attempts to change the amount or composition of lignin in relevant plant species have been hampered by the fact that the lignin biosynthetic pathway is difficult to understand, because it uses several enzymes for the same substrates, is regulated in an ill-characterized manner, may operate in different locations within cells, and contains metabolic channels, which the plant may use to funnel initial substrates into specific monolignols.ResultsWe propose a dynamic mathematical model that integrates various datasets and other information regarding the lignin pathway in Brachypodium distachyon and permits explanations for some counterintuitive observations. The model predicts the lignin composition and label distribution in a BdPTAL knockdown strain, with results that are quite similar to experimental data.ConclusionGiven the present scarcity of available data, the model resulting from our analysis is presumably not final. However, it offers proof of concept for how one may design integrative pathway models of this type, which are necessary tools for predicting the consequences of genomic or other alterations toward plants with lignin features that are more desirable than in their wild-type counterparts.

Chromosome-level reference genome and alternative splicing atlas of moso bamboo (Phyllostachys edulis)

BackgroundBamboo is one of the most important nontimber forestry products worldwide. However, a chromosome-level reference genome is lacking, and an evolutionary view of alternative splicing (AS) in bamboo remains unclear despite emerging omics data and improved technologies.ResultsHere, we provide a chromosome-level de novo genome assembly of moso bamboo (Phyllostachys edulis) using additional abundance sequencing data and a Hi-C scaffolding strategy. The significantly improved genome is a scaffold N50 of 79.90 Mb, approximately 243 times longer than the previous version. A total of 51,074 high-quality protein-coding loci with intact structures were identified using single-molecule real-time sequencing and manual verification. Moreover, we provide a comprehensive AS profile based on the identification of 266,711 unique AS events in 25,225 AS genes by large-scale transcriptomic sequencing of 26 representative bamboo tissues using both the Illumina and Pacific Biosciences sequencing platforms. Through comparisons with orthologous genes in related plant species, we observed that the AS genes are concentrated among more conserved genes that tend to accumulate higher transcript levels and share less tissue specificity. Furthermore, gene family expansion, abundant AS, and positive selection were identified in crucial genes involved in the lignin biosynthetic pathway of moso bamboo.ConclusionsThese fundamental studies provide useful information for future in-depth analyses of comparative genome and AS features. Additionally, our results highlight a global perspective of AS during evolution and diversification in bamboo.

Altered Lignin Content and Composition in Transgenic Populus trichocarpa Results in a Decrease of Modulus of Elasticity

Transgenic Populus trichocarpa wood was compared to the corresponding wild-type material. The static modulus of elasticity in three-point bending was measured and the chemical composition among the specimens were compared, including the glucose, xylose, and lignin contents as well as the S/G ratio. Changes in chemical composition, created by genetic manipulations of the lignin biosynthetic pathway, affect the mechanical properties of young small-diameter transgenic trees. There are indications that a decrease in lignin content causes severe reductions in mechanical properties. Changes in lignin structure, either from an increased S/G ratio or structural lignin modifications, also negatively influence the mechanical properties.

Overexpression of Sedum alfredii cinnamyl alcohol dehydrogenase increases the tolerance and accumulation of cadmium in Arabidopsis

Plant cell walls protect plants from heavy metal stress by resistance, transport and the adsorption process. Cell walls are impregnated with lignin, which enables structural integrity, long-distance water transport and protects plants from many types of stress. Cinnamyl alcohol dehydrogenase (CAD) is an essential enzyme that participates in the final step of the phenylpropanoid lignin biosynthetic pathway and plays an important role in the stress resistance process. In this study, we demonstrated that a CAD-encoding gene in the hyper-accumulating Sedum alfredii Hance, SaCAD, is constitutively expressed in all tissues. While the abundance of the SaCAD transcript is affected by cadmium (Cd) stress, it is upregulated in roots, stems and leaves during Cd treatment. Overexpression of SaCAD in transgenic Arabidopsis thaliana significantly increased CAD activities. Compared with the wild type (WT) plants, the Cd concentrations of SaCAD-overexpressing plants increased in the leaves and roots under Cd stress. The increased fixation of Cd to the thickened cell wall in the SaCAD-overexpressing A. thaliana plants resulted in better growth when the plants were grown in Cd stress conditions. In agreement with these data, SaCAD-overexpressing plants exhibited higher Cd tolerance compared to the wild type (WT) with higher chlorophyll and proline (Pro) contents and antioxidant enzyme activity, as well as a lower methane dicarboxylic aldehyde (MDA) content, electric conductivity and reactive oxygen species when exposed to Cd stress due to a lower amount of Cd distributed in the cytoplasm which is the most site of cytosolic metabolism. SaCAD was found to localize to the cytoplasm of tobacco cells. NMT analysis of the root tips from transgenic A. thaliana lines during Cd stress confirmed that SaCAD-overexpressing plants were capable of retaining more Cd in the cell wall in the Cd-supplied growth medium, which provided additional evidence for the potential role of SaCAD in heavy metal ion compartmentation and detoxification. In summary, we concluded that SaCAD performs critical functions in plants: Cd absorption and fixation to lignified cell wall during stress conditions.

Identification and expression profiling of genes governing lignin biosynthesis in Casuarina equisetifolia L.

Casuarina equisetifolia L. is an important multi-purpose, fast growing and widely planted tree species native to tropical and subtropical coastlines of Australia, Southeast Asia, Malaysia, Melanesia, Polynesia and New Caledonia. It is a nitrogen-fixing tree mainly used for charcoal making, construction poles, landscaping, timber, pulp, firewood, windbreaks, shelterbelts, soil erosion and sand dune stabilization. Casuarina wood is presently used for paper and pulp production. Raw material with reduced lignin is highly preferred to increase the pulp yield. Hence, understanding the molecular regulation of wood formation in this tree species is vital for selecting industrially suitable phenotypes for breeding programs. The lignin biosynthetic pathway has been extensively studied in tree species like Eucalypts, poplars, pines, Picea, Betula and Acacia sp. However, studies on wood formation at molecular level is presently lacking in casuarinas. Hence, in the present study, the transcriptome of the developing secondary tissues of 15 years old Casuarina equiseitfolia subsp. equisetifolia was sequenced, de novo assembled, annotated and mapped to functional pathways. Transcriptome sequencing generated a total of 26,985 transcripts mapped to 31 pathways. Mining of the annotated data identified nine genes involved in lignin biosynthesis pathway and relative expression of the transcripts in four tissues including scale-like leaves, needle-like brachlets, wood and root were documented. The expression of CeCCR1 and CeF5H were found to be significantly high in wood tissues, while maximum expression of CeHCT was documented in stem. Additionally, CeTUBA and CeH2A were identified as the most stable reference transcript for normalization of qRT-PCR data in C. equisetifolia. The present study is the first wood genomic resource in C. equisetifolia, which will be valuable for functional genomics research in this genus.

A wheat caffeic acid 3-O-methyltransferase TaCOMT-3D positively contributes to both resistance to sharp eyespot disease and stem mechanical strength

Plant caffeic acid 3-O-methyltransferase (COMT) has been implicated in the lignin biosynthetic pathway through catalyzing the multi-step methylation reactions of hydroxylated monomeric lignin precursors. However, genetic evidence for its function in plant disease resistance is poor. Sharp eyespot, caused primarily by the necrotrophic fungus Rhizoctonia cerealis, is a destructive disease in hexaploid wheat (Triticum aestivum L.). In this study, a wheat COMT gene TaCOMT-3D, is identified to be in response to R. cerealis infection through microarray-based comparative transcriptomics. The TaCOMT-3D gene is localized in the long arm of the chromosome 3D. The transcriptional level of TaCOMT-3D is higher in sharp eyespot-resistant wheat lines than in susceptible wheat lines, and is significantly elevated after R. cerealis inoculation. After R. cerealis inoculation and disease scoring, TaCOMT-3D-silenced wheat plants exhibit greater susceptibility to sharp eyespot compared to unsilenced wheat plants, whereas overexpression of TaCOMT-3D enhances resistance of the transgenic wheat lines to sharp eyespot. Moreover, overexpression of TaCOMT-3D enhances the stem mechanical strength, and lignin (particular syringyl monolignol) accumulation in the transgenic wheat lines. These results suggest that TaCOMT-3D positively contributes to both wheat resistance against sharp eyespot and stem mechanical strength possibly through promoting lignin (especially syringyl monolignol) accumulation.

Mathematical models of lignin biosynthesis

BackgroundLignin is a natural polymer that is interwoven with cellulose and hemicellulose within plant cell walls. Due to this molecular arrangement, lignin is a major contributor to the recalcitrance of plant materials with respect to the extraction of sugars and their fermentation into ethanol, butanol, and other potential bioenergy crops. The lignin biosynthetic pathway is similar, but not identical in different plant species. It is in each case comprised of a moderate number of enzymatic steps, but its responses to manipulations, such as gene knock-downs, are complicated by the fact that several of the key enzymes are involved in several reaction steps. This feature poses a challenge to bioenergy production, as it renders it difficult to select the most promising combinations of genetic manipulations for the optimization of lignin composition and amount.ResultsHere, we present several computational models than can aid in the analysis of data characterizing lignin biosynthesis. While minimizing technical details, we focus on the questions of what types of data are particularly useful for modeling and what genuine benefits the biofuel researcher may gain from the resulting models. We demonstrate our analysis with mathematical models for black cottonwood (Populus trichocarpa), alfalfa (Medicago truncatula), switchgrass (Panicum virgatum) and the grass Brachypodium distachyon.ConclusionsDespite commonality in pathway structure, different plant species show different regulatory features and distinct spatial and topological characteristics. The putative lignin biosynthes pathway is not able to explain the plant specific laboratory data, and the necessity of plant specific modeling should be heeded.

Characterization and analysis of CCR and CAD gene families at the whole-genome level for lignin synthesis of stone cells in pear (Pyrus bretschneideri) fruit.

ABSTRACTThe content of stone cells has significant effects on the flavour and quality of pear fruit. Previous research suggested that lignin deposition is closely related to stone cell formation. In the lignin biosynthetic pathway, cinnamoyl-CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), dehydrogenase/reductase family members, catalyse the last two steps in monolignol synthesis. However, there is little knowledge of the characteristics of the CCR and CAD families in pear and their involvement in lignin synthesis of stone cells. In this study, 31 CCRs and 26 CADs were identified in the pear genome. Phylogenetic trees for CCRs and CADs were constructed; key amino acid residues were analysed, and three-dimensional structures were predicted. Using quantitative real-time polymerase chain reaction (qRT-PCR), PbCAD2, PbCCR1, -2 and -3 were identified as participating in lignin synthesis of stone cells in pear fruit. Subcellular localization analysis showed that the expressed proteins (PbCAD2, PbCCR1, -2 and -3) are found in the cytoplasm or at the cell membrane. These results reveal the evolutionary features of the CCR and CAD families in pear as well as the genes responsible for regulation of lignin synthesis and stone cell development in pear fruit.

Dynamic metabolic reprogramming of steroidal glycol-alkaloid and phenylpropanoid biosynthesis may impart early blight resistance in wild tomato (Solanum arcanum Peralta).

Exploration with high throughput leaf metabolomics along with functional genomics in wild tomato unreveal potential role of steroidal glyco-alkaloids and phenylpropanoids during early blight resistance. Alternaria solani severely affects tomato (Solanum lycopersicum L.) yield causing early blight (EB) disease in tropical environment. Wild relative, Solanum arcanum Peralta could be a potential source of EB resistance; however, its underlying molecular mechanism largely remains unexplored. Hence, non-targeted metabolomics was applied on resistant and susceptible S. arcanum accessions upon A. solani inoculation to unravel metabolic dynamics during different stages of disease progression. Total 2047 potential metabolite peaks (mass signals) were detected of which 681 and 684 metabolites revealed significant modulation and clear differentiation in resistant and susceptible accessions, respectively. Majority of the EB-triggered metabolic changes were active from steroidal glycol-alkaloid (SGA), lignin and flavonoid biosynthetic pathways. Further, biochemical and gene expression analyses of key enzymes from these pathways positively correlated with phenotypic variation in the S. arcanum accessions indicating their potential role in EB. Additionally, transcription factors regulating lignin biosynthesis were also up-regulated in resistant plants and electrophoretic mobility shift assay revealed sequence-specific binding of rSaWRKY1 with MYB20 promoter. Moreover, transcript accumulation of key genes from phenylpropanoid and SGA pathways along with WRKY and MYB in WRKY1 transgenic tomato lines supported above findings. Overall, this study highlights vital roles of SGAs as phytoalexins and phenylpropanoids along with lignin accumulation unrevealing possible mechanistic basis of EB resistance in wild tomato.

Aluminum induced physiological and proteomic responses in tea (Camellia sinensis) roots and leaves

Tea (Camellia sinensis (L.) O. Kuntze), is an aluminum (Al) hyperaccumulator and grows well in acid soils. Although Al-induced growth of tea plant has been studied, the proteomic profiles of tea plants in response to Al are unclear. In the present study, the proteomic profiles in tea roots and leaves under Al stress were investigated using iTRAQ proteomics approach. In total, 755 and 1059 differentially expressed proteins were identified in tea roots and leaves, respectively. KEGG enrichment analysis showed that the differentially expressed proteins in roots were mainly involved in 11 pathways whereas those from leaves were mainly involved in 9 pathways. Abundance of most protein functions in glycolytic metabolism were enhanced in tea roots, and proteins involved in photosynthesis were stimulated in tea leaves. The protein ferulate-5-hydroxylase (F5H) in lignin biosynthetic pathway was down-regulated in both roots and leaves. Furthermore, antioxidant enzymes (ascorbate peroxidase, catalase and glutathione S-transferase) and citrate synthesis were accumulated in tea roots in response to Al. The results indicated that active photosynthesis and glycolysis as well as increased activities of antioxidant enzymes can be considered as a possible reason for the stimulatory effects of Al on the growth of tea plants. Additionally, the down-regulation of F5H and the binding of Al and phenolic acids may reduce the accumulation of lignin.