Research article

Phenolic compounds in ectomycorrhizal interaction of lignin modified silver birch

Suvi Sutela¹ , Karoliina Niemi² , Jaanika Edesi¹ , Tapio Laakso³ , Pekka Saranpää³ , Jaana Vuosku¹ , Riina Mäkelä¹ , Heidi Tiimonen⁴ , Vincent L Chiang⁵ , Janne Koskimäki¹ , Marja Suorsa¹ , Riitta Julkunen-Tiitto⁶ and Hely Häggman¹

¹Department of Biology, University of Oulu, PO Box 3000, 90014 Oulu, Finland

²Department of Applied Biology, University of Helsinki, PO Box 27, 00014 Helsinki, Finland

³Finnish Forest Research Institute, Vantaa Research Unit, Jokiniemenkuja 1, 01301 Vantaa, Finland

⁴Finnish Forest Research Institute, Punkaharju Research Unit, Finlandiantie 18, 58450 Punkaharju, Finland

⁵Forest Biotechnology Research Group, Department of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University, Campus Box 7247, 2500, Partners II Building, Raleigh, NC 27695-7247, USA

⁶Department of Biology, University of Joensuu, PO Box 111, 80101 Joensuu, Finland

author email corresponding author email

BMC Plant Biology 2009, 9:124doi:10.1186/1471-2229-9-124

Published:	29 September 2009

Abstract

Background

The monolignol biosynthetic pathway interconnects with the biosynthesis of other secondary phenolic metabolites, such as cinnamic acid derivatives, flavonoids and condensed tannins. The objective of this study is to evaluate whether genetic modification of the monolignol pathway in silver birch (Betula pendula Roth.) would alter the metabolism of these phenolic compounds and how such alterations, if exist, would affect the ectomycorrhizal symbiosis.

Results

Silver birch lines expressing quaking aspen (Populus tremuloides L.) caffeate/5-hydroxyferulate O-methyltransferase (PtCOMT) under the 35S cauliflower mosaic virus (CaMV) promoter showed a reduction in the relative expression of a putative silver birch COMT (BpCOMT) gene and, consequently, a decrease in the lignin syringyl/guaiacyl composition ratio. Alterations were also detected in concentrations of certain phenolic compounds. All PtCOMT silver birch lines produced normal ectomycorrhizas with the ectomycorrhizal fungus Paxillus involutus (Batsch: Fr.), and the formation of symbiosis enhanced the growth of the transgenic plants.

Conclusion

The down-regulation of BpCOMT in the 35S-PtCOMT lines caused a reduction in the syringyl/guaiacyl ratio of lignin, but no significant effect was seen in the composition or quantity of phenolic compounds that would have been caused by the expression of PtCOMT under the 35S or UbB1 promoter. Moreover, the detected alterations in the composition of lignin and secondary phenolic compounds had no effect on the interaction between silver birch and P. involutus.