The third most important food crop worldwide, potato (Solanum tuberosum L.) is a tetraploid outcrossing species propagated from tubers. Breeders have long been challenged by polyploidy, heterozygosity, and asexual reproduction. It has been assumed that tetraploidy is essential for high yield, that the creation of inbred potato is not feasible, and that propagation by seed tubers is ideal. In this paper, we question those assumptions and propose to convert potato into a diploid inbred line-based crop propagated by true seed. Although a conversion of this magnitude is unprecedented, the possible genetic gains from a breeding system based on inbred lines and the seed production benefits from a sexual propagation system are too large to ignore. We call on leaders of public and private organizations to come together to explore the feasibility of this radical and exciting new strategy in potato breeding.

The sphinganine analog mycotoxin, AAL-toxin, induces a death process in plant and animal cells that shows apoptotic morphology. In nature, the AAL-toxin is the primary determinant of the Alternaria stem canker disease of tomato, thus linking apoptosis to this disease caused by Alternaria alternata f. sp. lycopersici. The product of the baculovirus p35 gene is a specific inhibitor of a class of cysteine proteases termed caspases, and naturally functions in infected insects. Transgenic tomato plants bearing the p35 gene were protected against AAL-toxin-induced death and pathogen infection. Resistance to the toxin and pathogen co-segregated with the expression of the p35 gene through the T3 generation, as did resistance to A. alternata, Colletotrichum coccodes, and Pseudomonas syringae pv. tomato. The p35 gene, stably transformed into tomato roots by Agrobacterium rhizogenes, protected roots against a 30-fold greater concentration of AAL-toxin than control roots tolerated. Transgenic expression of a p35 binding site mutant (DQMD to DRIL), inactive against animal caspases-3, did not protect against AAL-toxin. These results indicate that plants possess a protease with substrate-site specificity that is functionally equivalent to certain animal caspases. A biological conclusion is that diverse plant pathogens co-opt apoptosis during infection, and that transgenic modification of pathways regulating programmed cell death in plants is a potential strategy for engineering broadspectrum disease resistance in plants.

Plant genetic engineering has, until now, relied on the incorporation of foreign DNA into plant genomes. Public concern about the extent to which transgenic crops differ from their traditionally bred counterparts has resulted in molecular strategies and gene choices that limit, but not eliminate, the introduction of foreign DNA. Here, we demonstrate that a plant-derived (P-) DNA fragment can be used to replace the universally employed Agrobacterium transfer (T-) DNA. Marker-free P-DNAs are transferred to plant cell nuclei together with conventional T-DNAs carrying a selectable marker gene. By subsequently linking a positive selection for temporary marker gene expression to a negative selection against marker gene integration, 29% of derived regeneration events contain P-DNA insertions but lack any copies of the T-DNA. Further refinements are accomplished by employing Ω-mutated virD2 and isopentenyl transferase cytokinin genes to impair T-DNA integration and select against backbone integration, respectively. The presented methods are used to produce hundreds of marker-free and backbone-free potato (Solanum tuberosum) plants displaying reduced expression of a tuber-specific polyphenol oxidase gene in potato. The modified plants represent the first example of genetically engineered plants that only contain native DNA

SummaryAcrylamide is produced in starchy foods that are baked, roasted or fried at high temperatures. Concerns about the potential health issues associated with the dietary intake of this reactive compound led us to reduce the accumulation of asparagine, one of its main precursors, in the tubers of potato ( Solanum tuberosum ). This metabolic change was accomplished by silencing two asparagine synthetase genes through 'all-native DNA' transformation. Glasshouse-grown tubers of the transformed intragenic plants contained up to 20-fold reduced levels of free asparagine. This metabolic change coincided with a small increase in the formation of glutamine and did not affect tuber shape or yield.Heat-processed products derived from the low-asparagine tubers were also indistinguishable from their untransformed counterparts in terms of sensory characteristics.However, both French fries and potato chips accumulated as little as 5% of the acrylamide present in wild-type controls. Given the important role of processed potato products in the modern Western diet, a replacement of current varieties with intragenic potatoes could reduce the average daily intake of acrylamide by almost one-third.

Summary