Lignin Pathway Research Articles

StMYB44 negatively regulates anthocyanin biosynthesis at high temperatures in tuber flesh of potato.

High temperatures are known to reduce anthocyanin accumulation in a number of diverse plant species. In potato (Solanum tuberosum L.), high temperature significantly reduces tuber anthocyanin pigment content. However, the mechanism of anthocyanin biosynthesis in potato tuber under heat stress remains unknown. Here we show that high temperature causes reduction of anthocyanin biosynthesis in both potato tuber skin and flesh, with white areas forming between the vasculature and periderm. Heat stress reduced the expression of the R2R3 MYB transcription factors (TFs) StAN1 and StbHLH1, members of the transcriptional complex responsible for coordinated regulation of the skin and flesh pigmentation, as well as anthocyanin biosynthetic pathway genes in white regions. However, the core phenylpropanoid pathway, lignin, and chlorogenic acid (CGA) pathway genes were up-regulated in white areas, suggesting that suppression of the anthocyanin branch may result in re-routing phenylpropanoid flux into the CGA or lignin biosynthesis branches. Two R2R3 MYB TFs, StMYB44-1 and StMYB44-2, were highly expressed in white regions under high temperature. In transient assays, StMYB44 represses anthocyanin accumulation in leaves of Nicotiana tabacum and N. benthamiana by directly suppressing the activity of the dihydroflavonol reductase (DFR) promoter. StMYB44-1 showed stronger repressive capacity than StMYB44-2, with both predicted proteins containing the repression-associated EAR motif with some variation. StMYB44-1 conferred repression without a requirement for a basic helix-loop-helix (bHLH) partner, suggesting a different repression mechanism from that of reported anthocyanin repressors. We propose that temperature-induced reduction of anthocyanin accumulation in potato flesh is caused by down-regulation of the activating anthocyanin regulatory complex, by enhancing the expression of flesh-specific StMYB44 and alteration of phenylpropanoid flux.

A comprehensive analysis of the Lactuca sativa, L. transcriptome during different stages of the compatible interaction with Rhizoctonia solani

The leafy green vegetable Lactuca sativa, L. is susceptible to the soil-born fungus Rhizoctonia solani AG1-IB. In a previous study, we reported on the transcriptional response of R. solani AG1-IB (isolate 7/3/14) during the interspecies interaction with L. sativa cv. Tizian by means of RNA sequencing. Here we present the L. sativa transcriptome and metabolome from the same experimental approach. Three distinct interaction zones were sampled and compared to a blank (non-inoculated) sample: symptomless zone 1, zone 2 showing light brown discoloration, and a dark brown zone 3 characterized by necrotic lesions. Throughout the interaction, we observed a massive reprogramming of the L. sativa transcriptome, with 9231 unique genes matching the threshold criteria for differential expression. The lettuce transcriptome of the light brown zone 2 presents the most dissimilar profile compared to the uninoculated zone 4, marking the main stage of interaction. Transcripts putatively encoding several essential proteins that are involved in maintaining jasmonic acid and auxin homeostasis were found to be negatively regulated. These and other indicator transcripts mark a potentially inadequate defence response, leading to a compatible interaction. KEGG pathway mapping and GC-MS metabolome data revealed large changes in amino acid, lignin and hemicellulose related pathways and related metabolites.

4-Coumarate 3-hydroxylase in the lignin biosynthesis pathway is a cytosolic ascorbate peroxidase

Lignin biosynthesis is evolutionarily conserved among higher plants and features a critical 3-hydroxylation reaction involving phenolic esters. However, increasing evidence questions the involvement of a single pathway to lignin formation in vascular plants. Here we describe an enzyme catalyzing the direct 3-hydroxylation of 4-coumarate to caffeate in lignin biosynthesis as a bifunctional peroxidase that oxidizes both ascorbate and 4-coumarate at comparable rates. A combination of biochemical and genetic evidence in the model plants Brachypodium distachyon and Arabidopsis thaliana supports a role for this coumarate 3-hydroxylase (C3H) in the early steps of lignin biosynthesis. The subsequent efficient O-methylation of caffeate to ferulate in grasses is substantiated by in vivo biochemical assays. Our results identify C3H as the only non-membrane bound hydroxylase in the lignin pathway and revise the currently accepted models of lignin biosynthesis, suggesting new gene targets to improve forage and bioenergy crops.

Proteomics Reveal the Profiles of Color Change in Brunfelsia acuminata Flowers.

Brunfelsia acuminata is a popular ornamental plant with different colors resulted from the rapid change of color after blooming. The petals at day one (purple), day three (white and purple) and day five (white) were used to analyze the reason of flower color change by a comparative proteomics approach, gas chromatography coupled to a time-of-flight mass analyzer (GC-TOF-MS) and quantitative real-time PCR (qRT-PCR). The results showed that the 52 identified proteins were classified into eight functional groups, 6% of which were related to the anthocyanin metabolic pathway. The expression levels of all anthocyanin proteins from the first day to fifth day were remarkably down-regulated, which was consistent with the changing patterns of the key genes (CHS, CHI and F3′5′H) in petals. Simultaneously, the main floral volatile components including Linalool and 2-Hexenal (E) were identified, and the contents of 2-Hexenal at day five increased dramatically. Moreover, the content of flavonoids and total phenolic increased at day five. The majority of the proteins associated with stress defense and senescence proteins were up-regulated and the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in the petals at day five were significantly higher than others. It was concluded that the competition in the precursors of metabolic pathways occurs and causes the flow of metabolite to the pathways of floral scent and lignin derived from the shikimate pathway or degrade into others. Therefore, the anthocyanin content significantly decreased, and the petal color changed from deep purple to white.

Deposition of lignin in four species of Saccharum

We used primers designed on conserved gene regions of several species to isolate the most expressed genes of the lignin pathway in four Saccharum species. S. officinarum and S. barberi have more sucrose in the culms than S. spontaneum and S. robustum, but less polysaccharides and lignin in the cell wall. S. spontaneum, and S. robustum had the lowest S/G ratio and a lower rate of saccharification in mature internodes. Surprisingly, except for CAD, 4CL, and CCoAOMT for which we found three, two, and two genes, respectively, only one gene was found for the other enzymes and their sequences were highly similar among the species. S. spontaneum had the highest expression for most genes. CCR and CCoAOMT B presented the highest expression; 4CL and F5H showed increased expression in mature tissues; C3H and CCR had higher expression in S. spontaneum, and one of the CADs isolated (CAD B) had higher expression in S. officinarum. The similarity among the most expressed genes isolated from these species was unexpected and indicated that lignin biosynthesis is conserved in Saccharum including commercial varieties Thus the lignin biosynthesis control in sugarcane may be only fully understood with the knowledge of the promotor region of each gene.

A Multilevel Study of Melon Fruit Reticulation Provides Insight into Skin Ligno-Suberization Hallmarks.

The skin of fleshy fruit is typically covered by a thick cuticle. Some fruit species develop different forms of layers directly above their skin. Reticulation, for example, is a specialized suberin-based coating that ornaments some commercially important melon (Cucumis melo) fruit and is an important quality trait. Despite its importance, the structural, molecular, and biochemical features associated with reticulation are not fully understood. Here, we performed a multilevel investigation of structural attributes, chemical composition, and gene expression profiles on a set of reticulated and smooth skin melons. High-resolution microscopy, surface profiling, and histochemical staining assays show that reticulation comprises cells with heavily suberized walls accumulating large amounts of typical suberin monomers, as well as lignified cells localized underneath the specialized suberized cell layer. Reticulated skin was characterized by induced expression of biosynthetic genes acting in the core phenylpropanoid, suberin, lignin, and lignan pathways. Transcripts of genes associated with lipid polymer assembly, cell wall organization, and loosening were highly enriched in reticulated skin tissue. These signatures were exclusive to reticulated structures and absent in both the smooth surfaces observed in between reticulated regions and in the skin of smooth fruit. Our data provide important insights into the molecular and metabolic bases of reticulation and its tight association with skin ligno-suberization during melon fruit development. Moreover, these insights are likely to contribute to melon breeding programs aimed at improving postharvest qualities associated with fleshy fruit surface layers.

Transcriptomic and Metabolic Profiling Reveals 'Green Ring' and 'Red Ring' on Jujube Fruit upon Postharvest Alternaria alternata Infection.

Alternaria alternata is the major threat to postharvest storage of jujube (Ziziphus jujuba Mill.) fruit. We found that natural A. alternata infection can cause very typical phenotype of 'green ring' and 'red ring' surrounding the disease spot on the jujube fruit. The phenotype was successfully modeled and constructed on jujubes by artificial inoculation with the pathogen. Furthermore, the pathogenic infection is evidenced essential to the onset of the phenotype. The 'red ring' circle is proved to be pre-fixed to block the 'green ring' area as a battlefield combating the pathogen's attack. We monitored the global transcriptomic profiling of 'green ring' and 'red ring' tissues from jujubes infected with A. alternata, in comparison with the mock-inoculated fruit and the control intact fruit. Large amount of differentially expressed genes were obtained in 'green ring', followed by 'red ring'. Transcriptional alterations associated with the core and peripheral phenylpropanoid and lignin pathways, plant hormonal metabolisms were greatly influenced in the 'green ring' and 'red ring' by the A. alternata infection. The integrated analysis of transcriptomic profiling and metabolic changes revealed the differentially but delicately coordinated activation of these biological processes in the 'green ring' and 'red ring' on jujubes in defensing the fungal infection.

Genomics and biochemistry investigation on the metabolic pathway of milled wood and alkali lignin-derived aromatic metabolites of Comamonas serinivorans SP-35

BackgroundThe efficient depolymerization and utilization of lignin are one of the most important goals for the renewable use of lignocelluloses. The degradation and complete mineralization of lignin by bacteria represent a key step for carbon recycling in land ecosystems as well. However, many aspects of this process remain unclear, for example, the complex network of metabolic pathways involved in the degradation of lignin and the catabolic pathway of intermediate aromatic metabolites. To address these subjects, we characterized the deconstruction and mineralization of lignin with milled wood lignin (MWL, the most representative molecule of lignin in its native state) and alkali lignin (AL), and elucidated metabolic pathways of their intermediate metabolites by a bacterium named Comamonas serinivorans SP-35.ResultsThe degradation rate of MWL reached 30.9%, and its particle size range was decreased from 6 to 30 µm to 2–4 µm—when cultured with C. serinivorans SP35 over 7 days. FTIR analysis showed that the C–C and C–O–C bonds between the phenyl propane structures of lignin were oxidized and cleaved and the side chain structure was modified. More than twenty intermediate aromatic metabolites were identified in the MWL and AL cultures based on GC–MS analysis. Through genome sequencing and annotation, and from GC–MS analysis, 93 genes encoding 33 enzymes and 5 regulatory factors that may be involved in lignin degradation were identified and more than nine metabolic pathways of lignin and its intermediates were predicted. Of particular note is that the metabolic pathway to form the powerful antioxidant 3,4-dihydroxyphenylglycol is described for the first time in bacteria.ConclusionElucidation of the β-aryl ether cleavage pathway in the strain SP-35 indicates that the β-aryl ether catabolic system is not only present in the family of Sphingomonadaceae, but also other species of bacteria kingdom. These newly elucidated catabolic pathways of lignin in strain SP-35 and the enzymes responsible for them provide exciting biotechnological opportunities for lignin valorization in future.

Regulation of cell wall development in Brachypodium distachyon in vitro as affected by cytokinin and gas exchange

Brachypodium distachyon is successfully used as a model grass species. The present study used molecular and chemical approaches to investigate the effects of the addition of the cytokinin 6-benzyladenine (BA) and two levels of gas exchange on the transcriptional regulation of lignin biosynthesis in B. distachyon. It was observed that the control of lignin biosynthesis is affected by both BA and the in vitro gas exchange rate, by sealing the vial with absence or presence of membranes. These observations are supported by anatomical and antioxidant enzyme activity analyses. However, the hyperhydricity caused by BA did not affect cell wall properties in B. distachyon. Interestingly, the CCR1 gene presented 70-fold increase in expression under the effect of BA and without membranes in addition to a significant increase in the peroxidases activity and total lignin content. Treatments with gas exchange showed higher qualitative accumulation of lignin S/G. Lignin pathway genes were transcriptionally coordinated according to the imposed treatment with apparent co-expression. Low expression of these genes was observed in the sealing treatment without membranes, while the opposite was verified in the condition of sealing with two membranes. CESA4 and CESA7 genes responded positively to gas exchange, without altering the cell wall cellulose/lignin ratio in B. distachyon. These results contribute to a better understanding of how cell wall-related gene expression is regulated by exogenous factors, as well as the many possibilities of cell wall manipulation due to its plasticity in adaptive responses.

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.

ChIP-Seq reveals that QsMYB1 directly targets genes involved in lignin and suberin biosynthesis pathways in cork oak (Quercus suber)

BackgroundGene activity is largely controlled by transcriptional regulation through the action of transcription factors and other regulators. QsMYB1 is a member of the R2R3-MYB transcription factor family related to secondary growth, and in particular, with the cork development process. In order to identify the putative gene targets of QsMYB1 across the cork oak genome we developed a ChIP-Seq strategy.ResultsResults provide direct evidence that QsMY1B targets genes encoding for enzymes involved in the lignin and suberin pathways as well as gene encoding for ABCG transporters and LTPs implicated in the transport of monomeric suberin units across the cellular membrane. These results highlight the role of QsMYB1 as a regulator of lignin and suberin biosynthesis, transport and assembly.ConclusionTo our knowledge, this work constitutes the first ChIP-Seq experiment performed in cork oak, a non-model plant species with a long-life cycle, and these results will contribute to deepen the knowledge about the molecular mechanisms of cork formation and differentiation.

Gene regulatory networks for lignin biosynthesis in switchgrass (Panicum virgatum).

SummaryCell wall recalcitrance is the major challenge to improving saccharification efficiency in converting lignocellulose into biofuels. However, information regarding the transcriptional regulation of secondary cell wall biogenesis remains poor in switchgrass (Panicum virgatum), which has been selected as a biofuel crop in the United States. In this study, we present a combination of computational and experimental approaches to develop gene regulatory networks for lignin formation in switchgrass. To screen transcription factors (TFs) involved in lignin biosynthesis, we developed a modified method to perform co‐expression network analysis using 14 lignin biosynthesis genes as bait (target) genes. The switchgrass lignin co‐expression network was further extended by adding 14 TFs identified in this study, and seven TFs identified in previous studies, as bait genes. Six TFs (PvMYB58/63, PvMYB42/85, PvMYB4, PvWRKY12, PvSND2 and PvSWN2) were targeted to generate overexpressing and/or down‐regulated transgenic switchgrass lines. The alteration of lignin content, cell wall composition and/or plant growth in the transgenic plants supported the role of the TFs in controlling secondary wall formation. RNA‐seq analysis of four of the transgenic switchgrass lines revealed downstream target genes of the secondary wall‐related TFs and crosstalk with other biological pathways. In vitro transactivation assays further confirmed the regulation of specific lignin pathway genes by four of the TFs. Our meta‐analysis provides a hierarchical network of TFs and their potential target genes for future manipulation of secondary cell wall formation for lignin modification in switchgrass.

Identification of genes revealed differential expression profiles and lignin accumulation during leaf and stem development in tea plant (Camellia sinensis (L.) O. Kuntze).

Lignin is a complex aromatic heteropolymer that plays essential roles in mechanical support, water transport, and response to biotic and abiotic stresses. The tea plant is a leaf-type beverage crop, which serves as a resource for non-alcoholic beverage tea. The content and distribution of lignin in tea plant leaves seriously affect the quality of tea. However, the biosynthetic pathways of lignin remain to be characterized in the tea plant. In the present study, lignin accumulation was investigated in tea plant leaves and stems at three developmental stages. The lignin content continuously increased during leaf and stem development in both tea plant cultivars 'Fudingdabai' and 'Suchazao.' The lignin distribution and anatomical characteristics of the tea plant leaves coincided with lignin accumulation and showed that lignin is mainly distributed in the epidermis, xylem, and vascular bundle sheath. 'Suchazao' exhibits a low lignin content and lacks a vascular bundle sheath. Twelve genes encoding the enzymes involved in the lignin biosynthesis of tea plant were identified and included CsPAL, CsC4H, Cs4CL, CsHCT, CsC3H, CsCCoAOMT, CsCCR, CsCAD, CsF5H, CsCOMT, CsPER, and CsLAC. The expression profiling of lignin biosynthesis-related genes and analysis of lignin accumulation may help elaborate the regulatory mechanisms of lignin biosynthesis in tea plant.

ITRAQ-Based Identification of Proteins Related to Lignin Synthesis in the Pear Pollinated with Pollen from Different Varieties

Most pears in Anhui Province are a kind of self-incompatible fruit whose quality is strongly influenced by the male pollen. The proteomic variation of Dangshan Su pollinated by different varieties was analysed using the isobaric tag for relative and absolute quantitation (iTRAQ) to investigate the effect of pollination by different varieties on the pear lignin pathway. Among the 3980 proteins identified from the two samples, 139 proteins were identified as differentially expressed proteins (DEPs). Of these proteins, laccase-4 (LAC4), was found to be related with lignin synthesis, and β-glucosidase 15 (BGLU15) and peroxidase 47 (PER47) were involved in the phenylpropanoid pathway. Moreover, the lignin and stone cell contents were lower in DW (Dangshan Su pollinated by Wonhwang) than those in DJ (Dangshan Su pollinated by Jingbaili). The effect of pollination on the synthesis of lignin through the regulation of the expression of PER47, BGLU15 and LAC4 ultimately affects the formation of stone cells and the fruit quality. We report for the first time that different pollinations influence the protein expression profile in the Dangshan Su pear, and this result provides some new epididymal targets for regulating the synthesis of lignin, regulating the content of stone cells and improving the quality of the pears.

Characterization of Cinnamyl Alcohol Dehydrogenase gene family in lignifying tissues of Tectona grandis L.f.

Abstract The cinnamyl alcohol dehydrogenase (CAD) enzyme catalyzes the last step of monolignols synthesis in the lignin pathway. Tectona grandis (teak) is a tropical tree with high valuable tim­ber. As there is few genetic information about lignin formation in teak, the purpose of this study is to characterize members of CAD family in this species. As methodology, PCR amplification using cDNA samples, vector cloning, sequencing, bioinforma­tics analyses and gene expression studies using real time RT-qPCR were performed. As results, four members (TgCAD1- TgCAD4) were obtained. Comparative analyses showed that all of them have conserved residues for catalytic zinc action, structural zinc ligation, NADPH binding and substrate specifici­ty, consistent with the mechanism of alcohol dehydrogenases. Phylogenetic analysis showed that TgCADs are present in three main classes and seven groups. Expression analyses revealed that TgCAD1 was highly expressed in leaves and could be rela­ted with pathogen defense. TgCAD2 was more expressed in branches and roots. Differently, TgCAD3 and TgCAD4 were highly expressed in juvenile and mature sapwood, suggesting a crucial role in wood development and lignin biosynthesis, with tissue-specialized expression profiles. Furthermore, TgCAD4 could be related with teak maturation for being more expressed in sapwood of mature teak trees. As conclusion, this work is the first to characterize genes of CAD family in Tectona grandis. These genes could be interesting to develop transge­nic plants for basic research and field applications.

Peculiarities of Pyrolysis of Hydrolytic Lignin in Dispersed Gas Phase and in Solid State

The unique decomposition pathways of hydrolytic lignin (HL) dissolved in an acetone/water mixture (9:1) and dispersed by a droplet evaporation technique under nitrogen gas flow has been investigated in a conventional reactor at atmospheric condition, a temperature region of 400–550 °C, and a residence time of 0.12 s. The results validate the fact that dispersion of the lignin into the gas phase by decreasing the sample size (as well as “minimizing the char area to avoid catalytic contact” of molecular products/radicals with the surface) may open new perspectives in understanding the chemistry of the depolymerization of lignin. Using Laser Desorption Ionization-Time of Flight-Mass Spectrometry (LDI-TOF-MS) the intrinsic ion m/z = 550, as the major MS peak from fresh HL dissolved in an acetone/water mixture before pyrolysis, was detected. Surprisingly, the expected phenolic compounds after pyrolysis were in trace amounts at less than 15% conversion of lignin. Instead, oligomeric intermediate substances with...

Genome-Wide Association Mapping and Genomic Selection for Alfalfa (Medicago sativa) Forage Quality Traits.

Genetic progress for forage quality has been poor in alfalfa (Medicago sativa L.), the most-grown forage legume worldwide. This study aimed at exploring opportunities for marker-assisted selection (MAS) and genomic selection of forage quality traits based on breeding values of parent plants. Some 154 genotypes from a broadly-based reference population were genotyped by genotyping-by-sequencing (GBS), and phenotyped for leaf-to-stem ratio, leaf and stem contents of protein, neutral detergent fiber (NDF) and acid detergent lignin (ADL), and leaf and stem NDF digestibility after 24 hours (NDFD), of their dense-planted half-sib progenies in three growing conditions (summer harvest, full irrigation; summer harvest, suspended irrigation; autumn harvest). Trait-marker analyses were performed on progeny values averaged over conditions, owing to modest germplasm × condition interaction. Genomic selection exploited 11,450 polymorphic SNP markers, whereas a subset of 8,494 M. truncatula-aligned markers were used for a genome-wide association study (GWAS). GWAS confirmed the polygenic control of quality traits and, in agreement with phenotypic correlations, indicated substantially different genetic control of a given trait in stems and leaves. It detected several SNPs in different annotated genes that were highly linked to stem protein content. Also, it identified a small genomic region on chromosome 8 with high concentration of annotated genes associated with leaf ADL, including one gene probably involved in the lignin pathway. Three genomic selection models, i.e., Ridge-regression BLUP, Bayes B and Bayesian Lasso, displayed similar prediction accuracy, whereas SVR-lin was less accurate. Accuracy values were moderate (0.3–0.4) for stem NDFD and leaf protein content, modest for leaf ADL and NDFD, and low to very low for the other traits. Along with previous results for the same germplasm set, this study indicates that GBS data can be exploited to improve both quality traits (by genomic selection or MAS) and forage yield.

Rapid Py-GC/MS assessment of the structural alterations of lignins in genetically modified plants

Genetic modifications for perturbing the lignin pathway in three different species of angiosperm plants, including non-woody (Arabidopsis and alfalfa) and woody (poplar) plants, were readily evaluated by analytical pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS). Pyrolysis showed that the composition of Arabidopsis plants was severely altered when the expression of the gene encoding the enzyme caffeic acid O-methyltransferase (COMT) was downregulated, resulting in a lignin largely enriched in guaiacyl (G) units (88%). Alfalfa plants in which lignin biosynthesis was modified by down-regulation of the p-coumarate 3-hydroxylase (C3H) gene, showed extremely high proportions of p-hydroxyphenyl (H) units (71%) relative to the naturally prevailing guaiacyl (G) and syringyl (S) units. Finally, Py-GC/MS analyses indicated that overexpression in poplar of the gene that encodes the enzyme ferulate 5-hydroxylase (F5H) resulted in a lignin with a higher content of syringyl lignin units (88%) compared to the wild-type control (71%). In conclusion, Py-GC/MS is a useful and convenient tool for the rapid evaluation of compositional changes in lignin from genetically modified plants.

Expression of phenylpropanoid and flavonoid pathway genes in oil palm roots during infection by Ganoderma boninense

The phenylpropanoid and flavonoid pathways are well known for their function towards plant development and defense. Oil palm seedlings from a single cross challenged with Ganoderma boninense displayed different severity of infection after six and fourteen months post inoculation (mpi). Transcripts from phenylpropanoid and flavonoid pathways, and transcription factors related to secondary cell wall formation were compared based on external and internal symptom classification. This long term infection study revealed that the oil palm roots responded to G. boninense and regulated both phenylpropanoid and flavonoid pathways during infection. The expression of PAL2 and PAL3 were significantly higher at 6mpi in symptomatic compared to asymptomatic and control seedlings. However, the expression of all PAL genes were down-regulated at 14mpi for both symptomatic and asymptomatic seedlings. In the monolignol and lignin pathways, down-regulation of COMT in symptomatic and CCR in asymptomatic seedlings was observed at 14mpi but not at 6mpi suggesting a possible change in lignin composition likely related to observed resistance. The expression of transcription factors for secondary cell wall and monolignol (MYB58, MYB63 and SND1) biosynthesis showed down-regulation in symptomatic seedlings, also suggesting a link between cell wall biosynthesis and disease resistance. Genes that regulate the flavonoid pathway were mostly down-regulated in both symptomatic seedlings at both 6mpi and 14mpi indicating a possibility of pathway suppression after challenge with G. boninense. Prolonged G. boninense exposure suggested that oil palm seedlings responded differently in terms of phenylpropanoid and flavonoid pathway expression in conferring defense and disease resistance.

ChemInform Abstract: The Occurrence of Tricin and Its Derivatives in Plants

AbstractReview: 186 refs.