Abstract
In this study, an EST library (EH663598–EH666265) obtained from xylogenic tissue cultures of tobacco that had been previously generated was annotated. The library proved to be enriched in transcripts related to the synthesis and modification of secondary cell walls. The xylem-specific transcripts for most of the genes of the lignification and xylan pathways were identified and several full-length sequences obtained. Gene expression was determined in available tobacco lines down-regulated for enzymes of the phenylpropanoid pathway: CINNAMATE 4-HYDROXYLASE (sc4h), CINNAMOYL-COA REDUCTASE (asccr) and lignification-specific peroxidase (asprx). In addition, lines down-regulated in the nucleotide-sugar pathway to xylan formation through antisense expression of UDP-GLUCURONIC ACID DECARBOXYLASE (asuxs) were also analysed. It is shown herein that most transcripts were down-regulated for both lignin and xylan synthesis pathways in these lines, while CELLULOSE SYNTHASE A3 was up-regulated in lignin-modified lines. The analysis indicates the existence of interdependence between lignin and xylan pathways at the transcriptional level and also shows that levels of cellulose, xylan and lignin are not necessarily directly correlated to differences in transcription of the genes involved upstream, as shown by cell wall fractionation and sugar analysis. It is therefore suggested that cell wall biosynthesis regulation occurs at different levels, and not merely at the transcriptional level. In addition, all lines analyzed showed improved enzymic saccharification of secondary but not primary walls. Nevertheless, this demonstrates potential industrial applicability for the approach undertaken to improve biomass utility.
Highlights
The efficiency of extraction and recovery of cellulose from cell walls influences many industrial processes including fibre production, pulp and paper-making and utilisation of biomass for biofuel
The cell wall is a complex laminate structure, which can be classified in dicots into three distinct zones, the middle lamella, the Abbreviations: ADH-like UDP-glucose dehydrogenase (ADH), bifunctional alcohol/UDP glucose dehydrogenase; AIM, acetone-insoluble material; CESA3, cellulose synthase; CSLD, cellulose synthaselike D; PHENYLALANINE AMMONIA-LYASE (PAL), phenylalanine ammonia lyase; CINNAMATE 4-HYDROXYLASES (C4H), cinnamate 4-hydroxylase; C3H, coumaroyl-ester-3-hydroxylase; Catechol O-methyltransferase (COMT), caffeic acid O-methyl transferase; Caffeoyl CoA O-methyltransferase (CCOMT), caffeoyl-CoA methyl-transferase; Cinnamoyl CoA reductase (CCR), cinnamoyl-CoA reductase; Cinnamyl alcohol dehydrogenase (CAD), cinnamyl alcohol dehydrogenase; HQT, hydroxycinnamoyl-CoA:quinate hydroxycinnamoyltransferase; Sucrose synthase (SUSY), sucrose synthase; UDP-glucose 6-dehydrogenase (UGD), UDP-glucose dehydrogenase; UDP-glucuronate decarboxylase (UXS), UDPglucuronate decarboxylase
These lines include: the sense orientation transgenic tobacco line for CINNAMATE 4-HYDROXYLASE, altered for the flux into the lignin pathway (Blee et al, 2001); the antisense transgenic lines for the CINNAMOYL-COA REDUCTASE, altered for monolignol composition (Piquemal et al, 1998); the lignification specific peroxidase TOBACCO PEROXIDASE 60, which was modified for lignin polymerisation (Blee et al, 2003; Kavousi et al, 2010) and the UDP-GLUCURONATE DECARBOXYLASE, modified for flux into the xylan synthesis pathway (Bindschedler et al, 2007)
Summary
The efficiency of extraction and recovery of cellulose from cell walls influences many industrial processes including fibre production, pulp and paper-making and utilisation of biomass for biofuel. An EST library generated using this system by Blee et al (2001a) is used here to direct transcriptional profiling of a panel of transgenic lines altered in lignin or hemicelluloses These lines include: the sense orientation transgenic tobacco line for CINNAMATE 4-HYDROXYLASE (referred to in the text as sc4h), altered for the flux into the lignin pathway (Blee et al, 2001); the antisense transgenic lines for the CINNAMOYL-COA REDUCTASE (asccr), altered for monolignol composition (Piquemal et al, 1998); the lignification specific peroxidase TOBACCO PEROXIDASE 60 (asprx), which was modified for lignin polymerisation (Blee et al, 2003; Kavousi et al, 2010) and the UDP-GLUCURONATE DECARBOXYLASE (asuxs), modified for flux into the xylan synthesis pathway (Bindschedler et al, 2007). All these lines showed improved enzymic saccharification demonstrating potential industrial applicability
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
