Potato is the world's most important vegetable crop, with nearly 400 million tons produced worldwide every year, lending to stability in food supply and socioeconomic impact. In general, potato is an intensively managed crop, requiring irrigation, fertilization, and frequent pesticide applications in order to obtain the highest yields possible. Important traits are easy to find in wild relatives of potato, but their introduction using traditional breeding can take 15–20 years. This is due to sexual incompatibility between some wild and cultivated species, a desire to remove undesirable wild species traits from adapted germplasm, and difficulty in identifying broadly applicable molecular markers. Fortunately, potato is amenable to propagation via tissue culture and it is relatively easy to introduce new traits using currently available biotech transformation techniques. For these reasons, potato is arguably the crop that can benefit most by modern biotechnology. The benefits of biotech potato, such as limited gene flow to conventionally grown crops and weedy relatives, the opportunity for significant productivity and nutritional quality gains, and reductions in production cost and environmental impact, have the potential to influence the marketability of newly developed varieties. In this review we will discuss current and past efforts to develop biotech potato varieties, traits that could be impacted, and the potential effects that biotech potato could have on the industry.

Despite intensive breeding efforts, potato late blight, caused by the oomycete pathogen Phytophthora infestans, remains a threat to potato production worldwide because newly evolved pathogen strains have consistently overcome major resistance genes. The potato RB gene, derived from the wild species Solanum bulbocastanum, confers resistance to most P. infestans strains through recognition of members of the pathogen effector family IPI-O. While the majority of IPI-O proteins are recognized by RB to elicit resistance (e.g. IPI-O1, IPI-O2), some family members are able to elude detection (e.g. IPI-O4). In addition, IPI-O4 blocks recognition of IPI-O1, leading to inactivation of RB-mediated programmed cell death. Here, we report results that elucidate molecular mechanisms governing resistance elicitation or suppression of RB by IPI-O. Our data indicate self-association of the RB coiled coil (CC) domain as well as a physical interaction between this domain and the effectors IPI-O4 and IPI-O1. We identified four amino acids within IPI-O that are critical for interaction with the RB CC domain and one of these amino acids, at position 129, determines hypersensitive response (HR) elicitation in planta. IPI-O1 mutant L129P fails to induce HR in presence of RB while IPI-O4 P129L gains the ability to induce an HR. Like IPI-O4, IPI-O1 L129P is also able to suppress the HR mediated by RB, indicating a critical step in the evolution of this gene family. Our results point to a model in which IPI-O effectors can affect RB function through interaction with the RB CC domain. The potato late blight pathogen, Phytophthora infestans, is able to rapidly evolve to overcome resistance genes. The pathogen accomplishes this by secreting an arsenal of proteins, termed effectors, that function to modify host cells. Although hundreds of candidate effectors have been identified in P. infestans, their roles in pathogenicity or virulence remains basically unknown. Our results showed that one of these effectors functions to turn off resistance mediated by the potato gene RB. This effector accomplishes this by directly interacting with RB, which likely modifies its ability to turn on host resistance. Further molecular analysis identified two amino acids within the effector that determine interaction, which can assist in developing appropriate disease control strategies.

The destructive plant disease potato late blight is caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary. This disease has remained particularly problematic despite intensive breeding efforts to integrate resistance into cultivated potato, largely because of the pathogen's ability to quickly evolve to overcome major resistance genes. The RB gene, identified in the wild potato species S. bulbocastanum, encodes a protein that confers broad-spectrum resistance to most P. infestans isolates through its recognition of highly conserved members of the corresponding pathogen effector family IPI-O. IpiO is a multigene family of effectors and while the majority of IPI-O proteins are recognized by RB to elicit host resistance, some variants exist that are able to elude detection (e.g. IPI-O4). In the present study, analysis of ipiO variants among 40 different P. infestans isolates collected from Guatemala, Thailand, and the United States revealed a high degree of complexity within this gene family. Isolate aggressiveness was correlated with increased ipiO diversity and especially the presence of the ipiO4 variant. Furthermore, isolates expressing IPI-O4 overcame RB-mediated resistance in transgenic potato plants even when the resistance-eliciting IPI-O1 variant was present. In support of this finding, we observed that expression of IPI-O4 via Agrobacterium blocked recognition of IPI-O1, leading to inactivation of RB-mediated programmed cell death in Nicotiana benthamiana. In this study we definitively demonstrate and provide the first evidence that P. infestans can defeat an R protein through inhibition of recognition of the corresponding effector protein.

Late blight (LB) of potato is considered one of the most devastating plant diseases in the world. Most cultivated potatoes are susceptible to this disease. However, wild relatives of potatoes are an excellent source of LB resistance. We screened 384 accessions of 72 different wild potato species available from the U.S. Potato GeneBank against the LB pathogen Phytophthora infestans in a detached leaf assay (DLA). P. infestans isolates US-23 and NL13316 were used in the DLA to screen the accessions. Although all plants in 273 accessions were susceptible, all screened plants in 39 accessions were resistant. Resistant and susceptible plants were found in 33 accessions. All tested plants showed a partial resistance phenotype in two accessions, segregation of resistant and partial resistant plants in nine accessions, segregation of partially resistant and susceptible plants in four accessions, and segregation of resistant, partially resistant, and susceptible individuals in 24 accessions. We found several species that were never before reported to be resistant to LB: Solanum albornozii, S. agrimoniifolium, S. chomatophilum, S. ehrenbergii, S. hypacrarthrum, S. iopetalum, S. palustre, S. piurae, S. morelliforme, S. neocardenasii, S. trifidum, and S. stipuloideum. These new species could provide novel sources of LB resistance. P. infestans clonal lineage-specific screening of selected species was conducted to identify the presence of RB resistance. We found LB resistant accessions in Solanum verrucosum, Solanum stoloniferum, and S. morelliforme that were susceptible to the RB overcoming isolate NL13316, indicating the presence of RB-like resistance in these species.

The goal of germplasm enhancement is to introgress traits from wild crop relatives into cultivated material and eventually cultivars. It seeks to restore genetic diversity that has been lost over time or to augment cultivated material with novel alleles that improve parents in breeding programs. This paper discusses potato germplasm enhancement efforts in the past, focusing on effective examples such as disease resistance and processing quality. In addition, it outlines new strategies for enhancement efforts, shifting the focus from evaluating phenotypes to tracking and manipulating specific DNA sequences. In the genomics era, germplasm enhancement will increasingly be focused on identifying and introgressing alleles rather than traits. Alleles will come from a broad pool of genetic resources that include wild species relatives of potato, landraces, cultivated potato itself, and distantly-related species. Genomics tools will greatly increase the efficiency of introgressing multi-genic traits and will make it possible to identify rare alleles and utilize recessive alleles.

Plants possess a robust and sophisticated innate immune system against pathogens and must balance growth with rapid pathogen detection and defense. The intracellular receptors with nucleotide-binding leucine-rich repeat (NLR) motifs recognize pathogen-derived effector proteins and thereby trigger the immune response. The expression of genes encoding NLR receptors is precisely controlled in multifaceted ways. The alternative splicing (AS) of introns in response to infection is recurrently observed but poorly understood. Here we report that the potato (Solanum tuberosum) NLR gene RB undergoes AS of its intron, resulting in two transcriptional isoforms, which coordinately regulate plant immunity and growth homeostasis. During normal growth, RB predominantly exists as intron-retained isoform RB_IR, encoding a truncated protein containing only the N-terminus of the NLR. Upon late blight infection, the pathogen induces intron splicing of RB, increasing the abundance of RB_CDS, which encodes a full-length and active R protein. By deploying the RB splicing isoforms fused with a luciferase reporter system, we identified IPI-O1 (also known as Avrblb1), the RB cognate effector, as a facilitator of RB AS. IPI-O1 directly interacts with potato splicing factor StCWC15, resulting in altered localization of StCWC15 from the nucleoplasm to the nucleolus and nuclear speckles. Mutations in IPI-O1 that eliminate StCWC15 binding also disrupt StCWC15 re-localization and RB intron splicing. Thus, our study reveals that StCWC15 serves as a surveillance facilitator that senses the pathogen-secreted effector and regulates the trade-off between RB-mediated plant immunity and growth, expanding our understanding of molecular plant–microbe interactions.