Holzforschung, Vol. 66, pp. 105–110, 2012 • Copyright  by Walter de Gruyter • Berlin • Boston. DOI 10.1515/HF.2011.144 2010/212 Article in press - uncorrected proof Fungal biodegradation of genetically modified and lignin-altered quaking aspen (Populus tremuloides Michx.) Richard Giles 1,a , Ilona Peszlen 1, *, Perry Peralta 1 , Hou-Min Chang 1 , Roberta Farrell 2 , Larry Grand 3 and Balazs Horvath 1 1 Department of Forest Biomaterials, North Carolina State University, Campus Box 8005, Raleigh, NC 27695-8005, USA 2 Department of Biological Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand 3 Department of Plant Pathology, North Carolina State University, Campus Box 7616, Raleigh, NC 27695-7616, USA *Corresponding author. Department of Forest Biomaterials, North Carolina State University, Campus Box 8005, Raleigh, NC 27695-8005, USA E-mail: ilona_peszlen@ncsu.edu Abstract Better access to wood carbohydrates as a result of reduced, or altered, lignin is a goal of biopulping, as well as biofuel research. In the present article, woods from three transgenic trees and one wild-type quaking aspen (Populus tremuloides Michx.) were analyzed in terms of mass loss of cellulose and lignin after incubation with lignocellulolytic fungi. The transgenic trees had reduced lignin content through transfer of an antisense -4CL gene, elevated syringyl/guaiacyl (S/G) ratio through insertion of a sense CAld5H gene and low lig- nin content and elevated S/G ratio through simultaneous insertion of -4CL and CAld5H genes, respectively. The lignocellulolytic fungi employed were a lignin-selective white rot fungus Ceriporiopsis subvermispora, a simultane- ous white rot fungus Trametes versicolor and a brown rot fungus Postia placenta. Reduced lignin degradation was observed in woods with increased S/G ratios indicating that this analytical feature influences decay resistance, regardless of the fungal decay mechanism. Keywords: biopulping; fungi; lignin; transgenic aspen. Introduction Lignin is a branched, and partly 3D-cross linked, aromatic polymer that arises from the radical co-polymerizations of the three monolignols: 4-hydroxy-cinnamic alcohol (H lignin), coniferyl alcohol (G lignin) and sinapyl alcohol (S lignin). The G lignins (in softwoods), the GS lignins (in hard- Present Address: Department of Biology, University of North Car- a olina at Charlotte, 365 Woodward Hall, Charlotte, NC 28223-0001, USA woods) and HGS lignins (in gramineaen) are combined with the polysaccharides within the cell wall into a special supra- molecular arrangement (Sarkanen and Ludwig 1971; Salme ´n and Burgert 2009; Stevanic and Salme ´n 2009). The lignin content of woods amounts to 15–36%, depending upon the species (Sarkanen and Ludwig 1971; Fengel and Wegener 1984; Eriksson et al. 1990). Lignin imparts to wood com- pressive strength and is also a physical and chemical barrier to lignocellulolytic enzymes. It was demonstrated that energy reduction and improve- ment of production efficiency are possible when pulping is performed by fungal pretreatment (biopulping) (Akhtar et al. 1992; Scott et al. 1998; Hakala et al. 2004; Ferraz et al. 2007; Masarin and Ferraz 2008; Vicentim and Ferraz 2008; Masa- rin et al. 2009; Vicentim et al. 2009; Xu et al. 2010). Fungal species suited to this purpose belong to the white rot decay that selectively metabolize lignin and largely leave carbo- hydrates intact; however, Ferraz et al. (2003) demonstrated that the carbohydrates are partly modified. The lignin type may also influence the efficiency of fungal decay (Obst et al. 1994); it was found that lignin-selective fungi prefer syringyl over guaiacyl lignin (Choi et al. 2006). The emerg- ing field of biorefinery and biofuel utilization (see overview by Dautzenberg et al. 2011) would benefit from wood spe- cies with diminished lignin content and/or altered lignin composition. A fungal pretreatment to this purpose would increase the efficiency of cellulolytic enzymes. In the last decade, several publications dealt with various aspects of transgenic trees, such as their specific problems of analysis (Akim et al. 2001; Yamada et al. 2006; Kasal et al. 2007), suitability for pulping (Tamura et al. 2001), or tissue development (Du ¨nisch et al. 2006). Transgenic aspens with reduced lignin content were also addressed (Hu et al. 1999; Li et al. 2001, 2003), which were produced by the insertion of the antisense 4CL gene. Expression of the insert- ed 4CL gene results in a block of one pathway for lignin monolignol production, resulting in reduced lignin content (Hu et al. 1999). The type of lignin produced has also been altered by the insertion of the sense CAld5H gene, which increases the syringyl/guaiacyl (S/G) lignin ratio (Li et al. 2001). Insertion of both genes leads to trees with lower lignin content and a higher S/G ratio (Li et al. 2003). Fungal pretreatment of transgenic trees with lowered lignin content could provide a novel solution to problems associated with the complex nature of polymers under par- ticipation of lignins and polysaccharides in the cell wall. Therefore, this exploratory study was conducted to evaluate the accessibility of the cell wall components to fungal activ- ity on genetically modified quaking aspen (Populus tremu- loides Michx.) with modified lignin contents and types. The specific objective was to determine the differences among Brought to you by | Michigan State University Authenticated | 35.8.11.2 Download Date | 11/27/13 12:12 PM