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Doctoral thesis2021Open access

Modification of forest trees by genetic engineering : from design to the field

Donev, Evgeniy


Developing viable genetic engineering methods for cell wall modification in trees is important to improve in a timely manner the properties of lignocellulose for biorefinery applications. New wood cell wall functionalities can be introduced by altered expression of native enzymes or by expressing microbial enzymes in planta. However, cell wall-modified plants could exhibit altered growth or other off-target effects. Understanding mechanisms of such effects will help to design better strategies for cell wall modification in woody crops dedicated to biorefinery. Hybrid aspen (Populus tremula L. x tremuloides Michx.) constitutively expressing glucuronoyl esterase from Phanerochaete carnosa Burt (PcGCE) has improved cellulose-to-glucose conversion but exhibits premature leaf senescence and immune defence reactions. Here I show that the observed untargeted effects are triggered by perception of PcGCE protein as a pathogen-associated molecular pattern (PAMP), and that these effects are avoided when PcGCE expression is limited to developing xylem cells by the wood-specific promoter. The findings stress importance of testing different microbial enzymes and using tissue-specific strategies of cell wall modification. Wood cell wall modification itself can trigger off-target effects by perception of damage-associated molecular patterns (DAMPs). This prompted a genome-wide identification and expression analysis of Populus malectin/malectin-like domaincontaining proteins, which include candidate receptors involved in secondary cell wall damage perception. Co-expression network analysis was used to identify their putative partners participating in cell wall damage signaling in developing wood. This knowledge will be important to develop strategies of wood cell wall modification, which will disarm the DAMP signaling pathway. Field conditions expose plants to multitude of biotic and abiotic stresses, revealing off-target phenotypes of genetically modified plants, which are not easily detected in greenhouse experiments. We have carried out two five-year trials with transgenic and intragenic hybrid aspen. The first one reports effects of reducing xylan acetylation using different methods. The second one describes growth and saccharification of lines having altered expression of xylogenesis-related genes, selected by large-scale greenhouse screenings. We found that reducing acetylation and avoiding off-target effects is possible with a right strategy. Further, tree growth was affected more by some genetic minipulations in the field than in the greenhouse. Saccharification analyses revealed that tree productivity plays most important role in determining glucose (Glc) yields per stem. The findings will help to design future biotechnological approaches to optimize trees for biorefinery.


transgenic trees; hybrid aspen; secondary cell wall; xylan; fungal enzymes; saccharification; field trial

Published in

Acta Universitatis Agriculturae Sueciae
2021, number: 2021:67
ISBN: 978-91-7760-811-0, eISBN: 978-91-7760-812-7
Publisher: Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences