Transgenic<i>Betula pendula</i>expressing sugar beet chitinase IV forms normal ectomycorrhizae with<i>Paxillus involutus in vitro</i>

bAmerican chestnut (Castanea dentata [Marsh.] Borkh.) dominated the eastern forests of North America, serving as a keystone species both ecologically and economically until the introduction of the chestnut blight, Cryphonectria parasitica, functionally eradicated the species. Restoration efforts include genetic transformation utilizing genes such as oxalate oxidase to produce potentially blight-resistant chestnut trees that could be released back into the native range. However, before such a release can be undertaken, it is necessary to assess nontarget impacts. Since oxalate oxidase is meant to combat a fungal pathogen, we are particularly interested in potential impacts of this transgene on beneficial fungi. This study compares ectomycorrhizal fungal colonization on a transgenic American chestnut clone expressing enhanced blight resistance to a wild-type American chestnut, a conventionally bred American-Chinese hybrid chestnut, and other Fagaceae species. A greenhouse bioassay used soil from two field sites with different soil types and land use histories. The number of colonized root tips was counted, and fungal species were identified using morphology, restriction fragment length polymorphism (RFLP), and DNA sequencing. Results showed that total ectomycorrhizal colonization varied more by soil type than by tree species. Individual fungal species varied in their colonization rates, but there were no significant differences between colonization on transgenic and wild-type chestnuts. This study shows that the oxalate oxidase gene can increase resistance against Cryphonectria parasitica without changing the colonization rate for ectomycorrhizal species. These findings will be crucial for a potential deregulation of blight-resistant American chestnuts containing the oxalate oxidase gene. E xotic pests and pathogens in North American forests have become increasingly significant problems, resulting in economic and ecological losses (1-5). One of the most famous is the introduction of chestnut blight, caused by the fungal pathogen Cryphonectria parasitica (Murr.) Barr, that nearly brought the American chestnut (Castanea dentata [Marsh.] Borkh.) to extinction (6). Prior to the blight, American chestnut dominated eastern U.S. hardwood forests, commonly comprising more than 25% and sometimes as much as 70% of the canopy (7,8). Following its removal as a top succession canopy species, many of the chestnut's former roles in the ecosystem were disrupted, resulting in both short-term effects and long-term impacts (2, 9).Chestnut was not only important ecologically but also played a significant role in the American economy. Fast growth and high tannin content made chestnut an asset to the lumber and leather industries (10). In addition to use in the leather industry, the high level of tannins in the wood and its resistance to water penetration due to extensive tylose formation (11) make it highly rot resistant and ideal for uses such as telephone poles, railway ties, and fencing (10, 12). American chestnut wood also was use...

Section: Discussionsupporting

confidence: 75%

Comparisons of Ectomycorrhizal Colonization of Transgenic American Chestnut with Those of the Wild Type, a Conventionally Bred Hybrid, and Related Fagaceae Species

D'Amico

Horton

Maynard

et al. 2015

“…Pleiotropic effects from GM trees coexpressing such selectable markers have also been recorded. For example, Pasonen et al (56) showed a significant decrease in the number of root tips colonized by Paxillus involutus associated with a line of chitinase-transformed silver birch in vitro. Similar results have been observed in vivo with P. involutus associated with a line of lignin-modified silver birches (72).…”

mentioning

confidence: 99%

Impact of an 8-Year-Old Transgenic Poplar Plantation on the Ectomycorrhizal Fungal Community

Stefani

Moncalvo

Séguin

et al. 2009

The long-term impact of field-deployed genetically modified trees on soil mutualistic organisms is not well known. This study aimed at evaluating the impact of poplars transformed with a binary vector containing the selectable nptII marker and ␤-glucuronidase reporter genes on ectomycorrhizal (EM) fungi 8 years after field deployment. We generated 2,229 fungal internal transcribed spacer (ITS) PCR products from 1,150 EM root tips and 1,079 fungal soil clones obtained from the organic and mineral soil horizons within the rhizosphere of three control and three transformed poplars. Fifty EM fungal operational taxonomic units were identified from the 1,706 EM fungal ITS amplicons retrieved. Rarefaction curves from both the root tips and soil clones were close to saturation, indicating that most of the EM species present were recovered. Based on qualitative and/or quantitative ␣-and ␤-diversity measurements, statistical analyses did not reveal significant differences between EM fungal communities associated with transformed poplars and the untransformed controls. However, EM communities recovered from the root tips and soil cloning analyses differed significantly from each other. We found no evidence of difference in the EM fungal community structure linked to the long-term presence of the transgenic poplars studied, and we showed that coupling root tip analysis with a soil DNA cloning strategy is a complementary approach to better document EM fungal diversity.

“…Crops, fruits, and forest trees exhibit mycorrhizal colonization by arbuscular mycorrhizae, ectomycorrhizae, and ectendomycorrhizae (EEM). While numerous studies have addressed the impact of transgenic plants on arbuscular mycorrhizae (10,26,64,68,72,73) and ectomycorrhizae (32,43,50,60), no previous study focused on EEM.…”

mentioning

confidence: 99%

Impact of Endochitinase-Transformed White Spruce on Soil Fungal Biomass and Ectendomycorrhizal Symbiosis

Stefani

Tanguay

Pelletier

et al. 2010

The impact of transgenic white spruce [Picea glauca (Moench) Voss] containing the endochitinase gene (ech42) on soil fungal biomass and on the ectendomycorrhizal fungi Wilcoxina spp. was tested using a greenhouse trial. The measured level of endochitinase in roots of transgenic white spruce was up to 10 times higher than that in roots of nontransformed white spruce. The level of endochitinase in root exudates of three of four ech42-transformed lines was significantly greater than that in controls. Analysis soil ergosterol showed that the amount of fungal biomass in soil samples from control white spruce was slightly larger than that in soil samples from ech42-transformed white spruce. Nevertheless, the difference was not statistically significant. The rates of mycorrhizal colonization of transformed lines and controls were similar. Sequencing the internal transcribed spacer rRNA region revealed that the root tips were colonized by the ectendomycorrhizal fungi Wilcoxina spp. and the dark septate endophyte Phialocephala fortinii. Colonization of root tips by Wilcoxina spp. was monitored by real-time PCR to quantify the fungus present during the development of ectendomycorrhizal symbiosis in ech42-transformed and control lines. The numbers of Wilcoxina molecules in the transformed lines and the controls were not significantly different (P > 0.05, as determined by analysis of covariance), indicating that in spite of higher levels of endochitinase expression, mycorrhization was not inhibited. Our results indicate that the higher levels of chitinolytic activity in root exudates and root tissues from ech42-transformed lines did not alter the soil fungal biomass or the development of ectendomycorrhizal symbiosis involving Wilcoxina spp.