All Plant Breeding Technologies Are Equal, but Some Are More Equal Than Others: The Case of GM and Mutagenesis

A pervasive opposition to genetically modified (GM) foods has developed from the notion that they pose a risk to human and environmental health. Other techniques for the genetic modification of plants, such as sexual crossing and mutagenesis breeding, have mostly remained unchallenged. This research aims to investigate public perception of plant breeding technologies. Specifically, sexual crossing, mutagenesis, transgenics (GM) and gene editing. It was expected that attitudes and intentions would be most positive and the perception of risk lowest for plant genetic modification through sexual crosses. Scores on these variables were expected to be similar between mutagenesis, GM and gene editing. It was also expected that attitudes, intentions and risk perception would change (becoming more positive) once participants learned about foods developed through these technologies. Participants reported their attitudes, intentions and risk perception at two points in time. At Time 2, they were presented with pictures of food items developed through sexual crossing, GM and mutagenesis. The results showed that mutagenesis stood out as the most negatively perceived technology, whereas genetic development via sexual crosses was generally perceived as positive. The results highlight the importance of messaging, framing in consumer attitudes.

The history of Botrytis taxonomy, the rise of phylogenetics, and implications for species recognition

Botrytis is one of the most well-studied, economically-important, and oldest fungal taxa. Nonetheless, many species in this genus have remained obscured for nearly 300 years due to the difficulty in distinguishing these species by conventional mycological methods. Aided by the use of phylogenetic tools, the genus is currently undergoing a taxonomic revolution. The number of putative species in the genus has nearly doubled over the last 10 years and more species are likely to be discovered into the future. The implementation of phylogenetic species recognition concepts in genus Botrytis is providing for more resolution on the relatedness among species than ever before and has helped to overcome issues in historical species recognition using morphology, sexual crosses, and pathogenicity trials. Meanwhile, the use of genetic tools is helping to reveal surprising insight into this archetypal necrotroph’s behavior, making these approaches increasingly important in species recognition and identification. As Botrytis taxonomy continues to evolve at a rapid pace, researchers should be encouraged to continue to employ the powerful tool of phylogenetics while considering how it fits into a larger framework of classical Botrytis species recognition. Starting points for discussion on how to move forward with Botrytis species recognition are included herein, with an emphasis on the implications and utility of new species descriptions.

Obtaining monokaryotic and dikaryotic mycelial cultures of two Amazonian strains of Geastrum (Geastraceae, Basidiomycota)

ABSTRACT The high diversity of the genus Geastrum and the difficulty of obtaining mycelial cultures impairs the study of the ecophysiology and the exploration of the biotechnological potential of the taxon. In this study, different culture media were tested to obtain mycelial cultures for G. lloydianum and G. subiculosum collected in the Brazilian Amazon. Data on spore germination, and isolation of monokaryotic cultures and in vitro sexual reproduction are presented, as well as a brief morphological description of the cultures obtained. For both species, Potato Dextrose Agar (PDA) was the most promising of the tested culture media. The highest growth in agar culture ever recorded for this genus is reported (4.9 mm per week for G. lloydianum and 7.5 mm for G. subiculosum). In the PDA culture medium, spores germinated after 35-40 days of incubation and the isolation of monokaryotic cultures of the two species, as well as in vitro sexual crosses, were successfully performed.

Diminishing-returns epistasis among random beneficial mutations in a multicellular fungus

Adaptive evolution ultimately is fuelled by mutations generating novel genetic variation. Non-additivity of fitness effects of mutations (called epistasis) may affect the dynamics and repeatability of adaptation. However, understanding the importance and implications of epistasis is hampered by the observation of substantial variation in patterns of epistasis across empirical studies. Interestingly, some recent studies report increasingly smaller benefits of beneficial mutations once genotypes become better adapted (called diminishing-returns epistasis) in unicellular microbes and single genes. Here, we use Fisher's geometric model (FGM) to generate analytical predictions about the relationship between the effect size of mutations and the extent of epistasis. We then test these predictions using the multicellular fungus Aspergillus nidulans by generating a collection of 108 strains in either a poor or a rich nutrient environment that each carry a beneficial mutation and constructing pairwise combinations using sexual crosses. Our results support the predictions from FGM and indicate negative epistasis among beneficial mutations in both environments, which scale with mutational effect size. Hence, our findings show the importance of diminishing-returns epistasis among beneficial mutations also for a multicellular organism, and suggest that this pattern reflects a generic constraint operating at diverse levels of biological organization.

Effect of linoleic acid on reproduction and yeast–mycelium dimorphism in the Dutch elm disease pathogens

Elm populations from North America and Europe were devastated by Dutch elm disease (DED), which is a vascular disease caused by fungi from the genus Ophiostoma (Ascomycota). These pathogens feature a yeast–mycelium dimorphism that may be related to virulence by facilitating colonization of the host xylem. Cyclooxygenases (COX) have been proposed to modulate yeast–mycelium dimorphism of DED fungi, and homologs of cox genes have been found in the nuclear genome of O. novo-ulmi subsp. novo-ulmi. Linoleic acid, a substrate for COX, was reported to stimulate the formation of asexual and sexual reproduction structures in DED strains grown on complex media. We hypothesized that linoleic acid also induced mycelium production in liquid shake culture conditions. Linoleic acid was found to enhance the production of reproductive structures in sexual crosses conducted on a complex medium (elm sapwood agar), but was not sufficient for these structures to form on a minimal medium. In liquid shake cultures grown in a minimal medium, the addition of linoleic acid stimulated mycelial formation. Our results suggest that linoleic acid plays a role in reproduction and dimorphism in the DED pathogens.

Virulence, Host-Selective Toxin Production, and Development of Three Cochliobolus Phytopathogens Lacking the Sfp-Type 4′-Phosphopantetheinyl Transferase Ppt1

The Sfp-type 4′-phosphopantetheinyl transferase Ppt1 is required for activation of nonribosomal peptide synthetases, including α-aminoadipate reductase (AAR) for lysine biosynthesis and polyketide synthases, enzymes that biosynthesize peptide and polyketide secondary metabolites, respectively. Deletion of the PPT1 gene, from the maize pathogen Cochliobolus heterostrophus and the rice pathogen Cochliobolus miyabeanus, yielded strains that were significantly reduced in virulence to their hosts. In addition, ppt1 mutants of C. heterostrophus race T and Cochliobolus victoriae were unable to biosynthesize the host-selective toxins (HST) T-toxin and victorin, respectively, as judged by bioassays. Interestingly, ppt1 mutants of C. miyabeanus were shown to produce tenfold higher levels of the sesterterpene-type non-HST ophiobolin A, as compared with the wild-type strain. The ppt1 strains of all species were also reduced in tolerance to oxidative stress and iron depletion; both phenotypes are associated with inability to produce extracellular siderophores biosynthesized by the nonribosomal peptide synthetase Nps6. Colony surfaces were hydrophilic, a trait previously associated with absence of C. heterostrophus Nps4. Mutants were decreased in asexual sporulation and C. heterostrophus strains were female-sterile in sexual crosses; the latter phenotype was observed previously with mutants lacking Nps2, which produces an intracellular siderophore. As expected, mutants were albino, since they cannot produce the polyketide melanin and were auxotrophic for lysine because they lack an AAR.

Rare interspecific breeding in Pseudo-nitzschia (Bacillariophyceae)

The biological species concept defines species based on sexual incompatibility between strains and the F1 sub-viability or inviability. However, to date, there is only a limited number of studies that formally deal with sexual incompatibility in unicellular protists and hence the rigorous application of biological species concept is fuzzy in these organisms. Here, we investigated interbreeding between two species of the planktonic pennate diatom Pseudo-nitzschia, P. arenysensis and P. pseudodelicatissima. We observed hybridization between these two species in controlled laboratory condition. The F1 generation showed: i) low viability; ii) morphological, ultrastructural, and morphometric features that resembled those of one of the parental strains (P. pseudodelicatissima); iii) intermediate maximum cell size to the one observed in intraspecific sexual crosses in the parental species. Our results may suggest that interbreeding between these two species is possible although likely rare. We invite a larger body of experimental evidence in unicellular protists to assess the applicability of the biological species concept to these organisms.

Evaluation of spontaneous generation of allelic variation in soybean in response to sexual hybridization and stress

Espinosa, K., Boelter, J., Lolle, S., Hopkins, M., Goggi, S., Palmer, R. G. and Sandhu, D. 2015. Evaluation of spontaneous generation of allelic variation in soybean in response to sexual hybridization and stress. Can. J. Plant Sci. 95: 405–415. Intra-cultivar variation reported in pure lines of soybean has been hypothesized to result from genetic mechanisms contributing to de novo genetic variation. In this study we have detected allele switching by following segregation patterns of Aconitase-4 isozyme in sexual crosses and pure lines. In sexual crosses, one F2 plant showed a switch at the Aconitase-4 (Aco4) locus from the expected heterozygous genotype Aco4-ac to Aco4-ab. In the pure lines grown in a honeycomb planting design and treated with an accelerated aging test, multiple cases of allele switching were detected at the Aco4 locus. Both single and double switches were detected that were stable and heritable. These findings indicate that the generation of endogenous variation continues in pure lines as a result of intrinsic genetic mechanisms. With a long-term goal of understanding the genetic nature of the changes, we genetically mapped the Aco4 gene to a 3.3 cM region on Chromosome 11. The corresponding physical region is ∼293 kb with 39 predicted genes. Of these, Glyma.11g080600 is of particular interest, as it shows 93% and 88% identity to Medicago truncatula and Arabidopsis aconitase genes, respectively. Further characterization of the soybean Aco4 gene may shed light on genetic mechanisms responsible for allele switching.