Inoculation of Transgenic Resistant Potato by Phytophthora infestans Affects Host Plant Choice of a Generalist Moth

Pathogen attack and the plant’s response to this attack affect herbivore oviposition preference and larval performance. Introduction of major resistance genes against Phytophthora infestans (Rpi-genes), the cause of the devastating late blight disease, from wild Solanum species into potato changes the plant-pathogen interaction dynamics completely, but little is known about the effects on non-target organisms. Thus, we examined the effect of P. infestans itself and introduction of an Rpi-gene into the crop on host plant preference of the generalist insect herbivore, Spodoptera littoralis (Lepidoptera: Noctuidae). In two choice bioassays, S. littoralis preferred to oviposit on P. infestans-inoculated plants of both the susceptible potato (cv. Desiree) and an isogenic resistant clone (A01-22: cv. Desiree transformed with Rpi-blb1), when compared to uninoculated plants of the same genotype. Both cv. Desiree and clone A01-22 were equally preferred for oviposition by S. littoralis when uninoculated plants were used, while cv. Desiree received more eggs compared to the resistant clone when both were inoculated with the pathogen. No significant difference in larval and pupal weight was found between S. littoralis larvae reared on leaves of the susceptible potato plants inoculated or uninoculated with P. infestans. Thus, the herbivore’s host plant preference in this system was not directly associated with larval performance. The results indicate that the Rpi-blb1 based resistance in itself does not influence insect behavior, but that herbivore oviposition preference is affected by a change in the plant-microbe interaction.     

Genome Analyses of an Aggressive and Invasive Lineage of the Irish Potato Famine Pathogen

Pest and pathogen losses jeopardise global food security and ever since the 19^th century Irish famine, potato late blight has exemplified this threat. The causal oomycete pathogen, Phytophthora infestans, undergoes major population shifts in agricultural systems via the successive emergence and migration of asexual lineages. The phenotypic and genotypic bases of these selective sweeps are largely unknown but management strategies need to adapt to reflect the changing pathogen population. Here, we used molecular markers to document the emergence of a lineage, termed 13_A2, in the European P. infestans population, and its rapid displacement of other lineages to exceed 75% of the pathogen population across Great Britain in less than three years. We show that isolates of the 13_A2 lineage are among the most aggressive on cultivated potatoes, outcompete other aggressive lineages in the field, and overcome previously effective forms of plant host resistance. Genome analyses of a 13_A2 isolate revealed extensive genetic and expression polymorphisms particularly in effector genes. Copy number variations, gene gains and losses, amino-acid replacements and changes in expression patterns of disease effector genes within the 13_A2 isolate likely contribute to enhanced virulence and aggressiveness to drive this population displacement. Importantly, 13_A2 isolates carry intact and in planta induced Avrblb1, Avrblb2 and Avrvnt1 effector genes that trigger resistance in potato lines carrying the corresponding R immune receptor genes Rpi-blb1, Rpi-blb2, and Rpi-vnt1.1. These findings point towards a strategy for deploying genetic resistance to mitigate the impact of the 13_A2 lineage and illustrate how pathogen population monitoring, combined with genome analysis, informs the management of devastating disease epidemics.     

Effects of Plant Nutrition on Susceptibility of Potato Leaves to Phytophthora infestans

A complete NPK fertilizer applied at planting, but not at later times, influenced the resistance of potato leaves to infection by Phytophthora infestans and the subsequent growth of lesions. Lesion size (7 days after inoculation) and lesion growth rate (between 7 and 9 days after inoculation) increased linearly with increasing fertilizer rates. Increasing rates of phosphate or potash, applied separately, did not significantly affect the development of blight lesions but a linear increase in lesion size was associated with increasing application rates of nitrogen.     

A 51 kDa Protein Kinase of Potato Activated with Hyphal Wall Components from Phytophthora infestans

In potato tuber tissue, treatment of fungal elicitor, hyphalwall components (HWC) induces various plant defense reactions.As treatment of protein kinase inhibitor prior to HWC treatmentblocks some of defense reactions induced by HWC, involvementof protein kinases in plant defense induction is proposed. Here,we demonstrate HWC-induced activation of a 51-kDa protein kinase(abbreviated p51-PK) using myelin basic protein as a substratein potato tuber discs. The activity of p51-PK was not detectedin the absence of phosphatase inhibitor, NaF, and p51-PK wasimmuroprecipitated with antibody against phosphotyrosine. Pretreatmentof phospholipase C inhibitor, neomycin, and GTP-binding proteinactivator, mastoparan, partially inhibited the HWC-induced activationof p51-PK, suggesting possible involvement of phospholipaseC and GTP-binding protein in the activation of p51-PK. Exogenouslysupplied elicitors, salicylic acid and arachidonic acid, whichare known to induce various defense responses in potato plants,also activated the protein kinase showing the same migrationas p51-PK on SDS-PAGE and different activation patterns. Theseresults implied that p51-PK might be involved in several signaltransduction pathways leading to plant defense responses initiatedby different stimuli. (Received January 11, 1999; Accepted May 25, 1999)     

The Role of Autophagy during Development of the Oomycete Pathogen Phytophthora infestans

Phytophthora infestans is a highly destructive plant path- ogen that causes late blight disease in plants such as potato and tomato （Fry and Goodwin, 1997）. As a typical oomycete, the primary infective propagule of P. infestans is the sporangium, which can either germinate directly or release biflagellate zoospores that encyst and germinate on the host subsequently （Grenville-Briggs et al., 2005）. Due to abundant formation of the sporangia and prolific sporulation, P. infestans can spread quickly in the host tissues and cause extensive necrosis of the infected plants （Kamoun and Smart, 2005）.     

Tracking historic migrations of the Irish potato famine pathogen,Phytophthora infestans

The plant pathogen Phytophthora infestans causes late blight, a devastating disease on potato that led to the Irish potato famine during 1845-1847. The disease is considered a reemerging problem and still causes major epidemics on both potato and tomato crops worldwide. Theories on the origin of the disease based on an examination of the genetic diversity and structure of P. infestans populations and use of historic specimens to understand modern day epidemics are discussed.     

The plant pathogen Phytophthora andina emerged via hybridization of an unknown Phytophthora species and the Irish potato famine pathogen, P. infestans

Emerging plant pathogens have largely been a consequence of the movement of pathogens to new geographic regions. Another documented mechanism for the emergence of plant pathogens is hybridization between individuals of different species or subspecies, which may allow rapid evolution and adaptation to new hosts or environments. Hybrid plant pathogens have traditionally been difficult to detect or confirm, but the increasing ease of cloning and sequencing PCR products now makes the identification of species that consistently have genes or alleles with phylogenetically divergent origins relatively straightforward. We investigated the genetic origin of Phytophthora andina, an increasingly common pathogen of Andean crops Solanum betaceum, S. muricatum, S. quitoense, and several wild Solanum spp. It has been hypothesized that P. andina is a hybrid between the potato late blight pathogen P. infestans and another Phytophthora species. We tested this hypothesis by cloning four nuclear loci to obtain haplotypes and using these loci to infer the phylogenetic relationships of P. andina to P. infestans and other related species. Sequencing of cloned PCR products in every case revealed two distinct haplotypes for each locus in P. andina, such that each isolate had one allele derived from a P. infestans parent and a second divergent allele derived from an unknown species that is closely related but distinct from P. infestans, P. mirabilis, and P. ipomoeae. To the best of our knowledge, the unknown parent has not yet been collected. We also observed sequence polymorphism among P. andina isolates at three of the four loci, many of which segregate between previously described P. andina clonal lineages. These results provide strong support that P. andina emerged via hybridization between P. infestans and another unknown Phytophthora species also belonging to Phytophthora clade 1c.     

Pyrophosphate-stimulated uptake of calcium into the germlings of Phytophthora infestans.

The uptake of 1 micrometer calcium into 6-h-old germination tubes of the fungus Phytophthora infestans follows Michaelis-Menten kinetics with a Km of 33 +/- 4 micrometer and a V of 0.3 nmol.min-1.(5 x 10(4) cells)-1.Uptake is inhibited by ruthenium red and lanthanum (both at 1 micrometer) and by the proton conductors 2,4-dinitrophenol (1 mM) and carbonylcyanide m-chlorophenylhydrazone and carbonylcyanide p-trifluoromethoxyphenylhydrazone (1--10 micrometer) and also by sodium azide. These data suggest that calcium uptake is dependent on energy and on a carrier. Calcium uptake is stimulated by pyrophosphate but not by ATP, orthophosphate, or polyphosphate. This stimulation is prevented by proton conductors or by incubation at 0 degrees C.     

利用抑制差减杂交技术分离马铃薯晚疫病抗性相关基因

以晚疫病病原菌混合小种接种处理48h的马铃薯水平抗性材料(R-gene-free)叶片为目的材料,以未处理材料作为对照,用抑制差减杂交技术构建了一个富集晚疫病抗性相关基因的差减文库。应用反向Northern技术对840个克隆进行斑点杂交筛选,筛选出150个病原诱导后信号明显增强的克隆。26个片段测序结果表明：部分片段基因功能与抗病性明显相关。7个差异表达片段与GenBank EST数据库中已有晚疫病原诱导马铃薯叶片得到的EST有很高同源性(达95％～100％);部分片段核苷酸或氨基酸序列分别与番茄、烟草、拟南芥等的EST序列或氨基酸序列有较高同源性;另有4个基因片段在GenBank EST数据库中未找到明显的同源序列,可能为新发现的基因片段。     

Nucleotide-binding leucine-rich repeat network underlies nonhost resistance of pepper against the Irish potato famine pathogen Phytophthora infestans

Nonhost resistance (NHR) is a robust plant immune response against non-adapted pathogens. A number of nucleotide-binding leucine-rich repeat (NLR) proteins that recognize non-adapted pathogens have been identified, although the underlying molecular mechanisms driving robustness of NHR are still unknown. Here, we screened 57 effectors of the potato late blight pathogen Phytophthora infestans in nonhost pepper (Capsicum annuum) to identify avirulence effector candidates. Selected effectors were tested against 436 genome-wide cloned pepper NLRs, and we identified multiple functional NLRs that recognize P. infestans effectors and confer disease resistance in the Nicotiana benthamiana as a surrogate system. The identified NLRs were homologous to known NLRs derived from wild potatoes that recognize P. infestans effectors such as Avr2, Avrblb1, Avrblb2, and Avrvnt1. The identified CaRpi-blb2 is a homologue of Rpi-blb2, recognizes Avrblb2 family effectors, exhibits feature of lineage-specifically evolved gene in microsynteny and phylogenetic analyses, and requires pepper-specific NRC (NLR required for cell death)-type helper NLR for proper function. Moreover, CaRpi-blb2–mediated hypersensitive response and blight resistance were more tolerant to suppression by the PITG_15 278 than those mediated by Rpi-blb2. Combined results indicate that pepper has stacked multiple NLRs recognizing effectors of non-adapted P. infestans, and these NLRs could be more tolerant to pathogen-mediated immune suppression than NLRs derived from the host plants. Our study suggests that NLRs derived from nonhost plants have potential as untapped resources to develop crops with durable resistance against fast-evolving pathogens by stacking the network of nonhost NLRs into susceptible host plants.     

Trade‐offs and evolution of thermal adaptation in the Irish potato famine pathogen Phytophthora infestans

Temperature is one of the most important environmental parameters with crucial impacts on nearly all biological processes. Due to anthropogenic activity, average air temperatures are expected to increase by a few degrees in coming decades, accompanied by an increased occurrence of extreme temperature events. Such global trends are likely to have various major impacts on human society through their influence on natural ecosystems, food production and biotic interactions, including diseases. In this study, we used a combination of statistical genetics, experimental evolution and common garden experiments to investigate the evolutionary potential for thermal adaptation in the potato late blight pathogen, Phytophthora infestans, and infer its likely response to changing temperatures. We found a trade‐off associated with thermal adaptation to heterogeneous environments in P. infestans, with the degree of the trade‐off peaking approximately at the pathogen's optimum growth temperature. A genetic trade‐off in thermal adaptation was also evidenced by the negative association between a strain's growth rate and its thermal range for growth, and warm climates selecting for a low pathogen growth rate. We also found a mirror effect of phenotypic plasticity and genetic adaptation on growth rate. At below the optimum, phenotypic plasticity enhances pathogen's growth rate but nature selects for slower growing genotypes when temperature increases. At above the optimum, phenotypic plasticity reduces pathogen's growth rate but natural selection favours for faster growing genotypes when temperature increases further. We conclude from these findings that the growth rate of P. infestans will only be marginally affected by global warming.     

Local adaptation to temperature in populations and clonal lineages of the Irish potato famine pathogen Phytophthora infestans

Environmental factors such as temperature strongly impact microbial communities. In the current context of global warming, it is therefore crucial to understand the effects of these factors on human, animal, or plant pathogens. Here, we used a common‐garden experiment to analyze the thermal responses of three life‐history traits (latent period, lesion growth, spore number) in isolates of the potato late blight pathogen Phytophthora infestans from different climatic zones. We also used a fitness index (FI) aggregating these traits into a single parameter. The experiments revealed patterns of local adaptation to temperature for several traits and for the FI, both between populations and within clonal lineages. Local adaptation to temperature could result from selection for increased survival between epidemics, when isolates are exposed to more extreme climatic conditions than during epidemics. We also showed different thermal responses among two clonal lineages sympatric in western Europe, with lower performances of lineage 13_A2 compared to 6_A1, especially at low temperatures. These data therefore stress the importance of thermal adaptation in a widespread, invasive pathogen, where adaptation is usually considered almost exclusively with respect to host plants. This must now be taken into account to explain, and possibly predict, the global distribution of specific lineages and their epidemic potential.