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Summary: Rye (Secale cereale), a valuable relative of wheat, contains abundant powdery mildew resistance (Pm) genes. Using physical mapping, transcriptome sequencing, barley stripe mosaic virus‐induced gene silencing, ethyl methane sulfonate mutagenesis, and stable transformation, we isolated and validated two coiled‐coil, nucleotide‐binding site and leucine‐rich repeat (CC‐NBS‐LRR) alleles, PmTR1 and PmTR3, located on rye chromosome 6RS from different triticale lines. PmTR1 confers age‐related resistance starting from the three‐leaf stage, whereas its allele, PmTR3, confers typical all‐stage resistance, which may be associated with their differential gene expression patterns. Overexpression in Nicotiana benthamiana showed that the CC, CC‐NBS, and CC‐LRR fragments of PMTR1 induce cell death, whereas in PMTR3 the CC and full‐length fragments perform this function. Luciferase complementation imaging and pull‐down assays revealed distinct interaction activities between the CC and NBS fragments. Our study elucidates two novel rye‐derived Pm genes and their derivative germplasm resources and provides novel insights into the mechanism of age‐related resistance, which can aid the improvement of resistance against wheat powdery mildew. [ABSTRACT FROM AUTHOR]

Phytophthora fruit rot (PFR) caused by the soilborne oomycete pathogen, Phytophthora capsici, can cause severe yield loss in cucumber. With no resistant variety available, genetic resources are needed to develop resistant varieties. The goal of this work was to identify quantitative trait loci (QTL) associated with resistance to PFR using multiple genomic approaches and populations. Two types of resistances have been identified: age-related resistance (ARR) and young fruit resistance. ARR occurs at 12-16 days post pollination (dpp), coinciding with the end of exponential fruit growth. A major QTL for ARR was discovered on chromosome 3 and a candidate gene identified based on comparative transcriptomic analysis. Young fruit resistance, which is observed during the state of rapid fruit growth prior to commercial harvest, is a quantitative trait for which multiple QTL were identified. The largest effect QTL, qPFR5.1, located on chromosome 5 was fine mapped to a 1-Mb region. Genome-wide association studies (GWAS) and extreme-phenotype genomewide association study (XP-GWAS) for young fruit resistance were also performed on a cucumber core collection representing > 96% of the genetic diversity of the USDA cucumber germplasm. Several SNPs overlapped with the QTL identified from QTL-seq analysis on biparental populations. In addition, novel SNPs associated with the resistance were identified from the germplasm. The resistant alleles were found mostly in accessions from India and South Asia, the center of diversity for cucumber. The results from this work can be applied to future disease resistance studies and marker-assisted selection in breeding programs. [ABSTRACT FROM AUTHOR]

Abstract Background Age-related resistance (ARR) is a developmentally regulated phenomenon conferring resistance to pathogens or pests. Although ARR has been observed in several host-pathogen systems, the underlying mechanisms are largely uncharacterized. In cucumber, rapidly growing fruit are highly susceptible to Phytophthora capsici but become resistant as they complete exponential growth. We previously demonstrated that ARR is associated with the fruit peel and identified gene expression and metabolomic changes potentially functioning as preformed defenses. Results Here, we compare the response to infection in fruit at resistant and susceptible ages using microscopy, quantitative bioassays, and weighted gene co-expression analyses. We observed strong transcriptional changes unique to resistant aged fruit 2–4 h post inoculation (hpi). Microscopy and bioassays confirmed this early response, with evidence of pathogen death and infection failure as early as 4 hpi and cessation of pathogen growth by 8–10 hpi. Expression analyses identified candidate genes involved in conferring the rapid response including those encoding transcription factors, hormone signaling pathways, and defenses such as reactive oxygen species metabolism and phenylpropanoid biosynthesis. Conclusion The early pathogen death and rapid defense response in resistant-aged fruit provide insight into potential mechanisms for ARR, implicating both pre-formed biochemical defenses and developmentally regulated capacity for pathogen recognition as key factors shaping age-related resistance.

Regardless of variable environmental conditions and changing pathogen populations, the Estonian potato cultivar (cv.) Ando has shown elevated field resistance to Phytophthora infestans for over 40 years. One of cv. Ando’s parents, the Latvian cultivar Agra, is considered a cultivar of medium to low resistance, the other parent, line 382-48, has a well-known source of resistance, Solanum demissum, in its pedigree. Segregation of late blight disease severity in a population of 95 hybrid plants from cv. Ando’s backcross to cv. Agra (cv. Ando x cv. Agra BC1) in field trials of three consecutive years (2013−2015) and in a test of a single pathogen isolate fits a model of additive action of multiple unlinked race-specific resistance genes responsible for the field resistance of cv. Ando. At least some of the resistance genes in cv. Ando’s genome do not function in juvenile plants and are developmentally upregulated.

Tomato yellow leaf curl virus (TYLCV) is one of the most notorious plant pathogens affecting the production of tomato worldwide. While the occurrence of age-related resistance (ARR) against TYLCV has been reported, the factors impacting its development remain unknown. We conducted a series of experiments with three tomato cultivars that vary in basal resistance to TYLCV to explore factors involved in the development of ARR. Our data indicate that ARR is more pronounced in tomato cultivars with higher basal resistance. Additionally, increased plant biomass in older plants does not contribute to ARR. Virus source plants with a younger age at initial inoculation facilitates virus acquisition by whiteflies. Finally, an analysis on plant hormones suggests that salicylic acid (SA) may play a major role in the development of ARR in tomato against TYLCV. These findings provide new insights into the developmental resistance in tomato against TYLCV as well as clues for the deployment of ARR in the management of diseases caused by TYLCV.

Tomato yellow leaf curl virus (TYLCV) is one of the most notorious plant pathogens affecting the production of tomato worldwide. While the occurrence of age-related resistance (ARR) against TYLCV has been reported, the factors impacting its development remain unknown. We conducted a series of experiments with three tomato cultivars that vary in basal resistance to TYLCV to explore factors involved in the development of ARR. Our data indicate that ARR is more pronounced in tomato cultivars with higher basal resistance. Additionally, increased plant biomass in older plants does not contribute to ARR. Virus source plants with a younger age at initial inoculation facilitates virus acquisition by whiteflies. Finally, an analysis on plant hormones suggests that salicylic acid (SA) may play a major role in the development of ARR in tomato against TYLCV. These findings provide new insights into the developmental resistance in tomato against TYLCV as well as clues for the deployment of ARR in the management of diseases caused by TYLCV. [ABSTRACT FROM AUTHOR]

Bud rot (BR) is the most devastating disease affecting oil palm (Elaeis guineensis) crops in Colombia. Its causal agent, Phytophthora palmivora, initiates the infection in immature oil palm leaflets producing necrotic lesions, followed by colonization of opportunistic necrotrophs, which increases disease damage. To improve the characterization of the disease, we transformed P. palmivora using Agrobacterium tumefaciens-mediated transformation (ATMT) to include the fluorescent proteins CFP-SKL (peroxisomal localization), eGFP and mRFP1 (cytoplasmic localization). The stability of some transformants was confirmed by Southern blot analysis and single zoospore cultures; additionally, virulence and in vitro growth were compared to the wild-type isolate to select transformants with the greatest resemblance to the WT isolate. GFP-tagged P. palmivora was useful to identify all of the infective structures that are commonly formed by hemibiotrophic oomycetes, including apoplastic colonization and haustorium formation. Finally, we detected cell death responses associated with immature oil palm tissues that showed reduced susceptibility to P. palmivora infection, indicating that these tissues could exhibit age-related resistance. The aim of this research is to improve the characterization of the initial disease stages and generate cell biology tools that may be useful for developing methodologies for early identification of oil palm materials resistant or susceptible to BR.

Myrtle rust (Austropuccinia psidii) is an invasive species causing damage to Myrtaceae species in natural and managed ecosystems in many countries. To better understand myrtle rust epidemiology we studied latent period (LP) and ontogenic resistance in relation to temperature on three susceptible hosts (Metrosideros excelsa, Lophomyrtus bullata × L. obcordata and Syzygium jambos). The latent period curve was U‐shaped, with latent development >0 from between 8 and 10 °C, depending on the host, to 32 °C. Optimum range was 22–28 °C with minimum LP of 5–7 days. Peak spore production occurred over about 2 weeks, starting about 1 week after the LP ended. Some spore production continued for 1–2 months. Comparison of the LP data with field temperatures indicated that the uredinial stage of A. psidii can overwinter in the latent phase in temperate areas of New Zealand and southern Australia and, therefore, uredinial or telial reinfection is not required during winter. The LP information was used to correct the LP function in a New Zealand myrtle rust climatic risk model. The transition of emergent leaf and stem tissues in susceptible Myrtaceae genotypes from susceptible to immune (ontogenic resistance) was characterized in terms of uredinium density and LP. Onset of ontogenic resistance was closely linked to the degree of leaf expansion, with fully expanded leaves being immune to infection. Because ontogenic resistance restricts infection to periods when growth flushes occur, understanding it is crucial for explaining the seasonality of myrtle rust development in the natural environment. [ABSTRACT FROM AUTHOR]

Regardless of variable environmental conditions and changing pathogen populations, the Estonian potato cultivar (cv.) Ando has shown elevated field resistance to Phytophthora infestans for over 40 years. One of cv. Ando's parents, the Latvian cultivar Agra, is considered a cultivar of medium to low resistance, the other parent, line 382-48, has a well-known source of resistance, Solanum demissum, in its pedigree. Segregation of late blight disease severity in a population of 95 hybrid plants from cv. Ando's backcross to cv. Agra (cv. Ando x cv. Agra BC1) in field trials of three consecutive years (2013−2015) and in a test of a single pathogen isolate fits a model of additive action of multiple unlinked race-specific resistance genes responsible for the field resistance of cv. Ando. At least some of the resistance genes in cv. Ando's genome do not function in juvenile plants and are developmentally upregulated. [ABSTRACT FROM AUTHOR]

We recently discovered that β‐aminobutyric acid (BABA), a molecule known for its ability to prime defences in plants, is a natural plant metabolite. However, the role played by endogenous BABA in plants is currently unknown. In this study we investigated the systemic accumulation of BABA during pathogen infection, levels of BABA during plant growth and development and analysed mutants possibly involved in BABA transport or regulation.BABA was quantified by LC‐MS using an improved method adapted from a previously published protocol. Systemic accumulation of BABA was determined by analysing non‐infected leaves and roots after localised infections with Plectosphaerella cucumerina or Pseudomonas syringae pv. tomato (Pst) DC3000 avrRpt2. The levels of BABA were also quantified in different plant tissues and organs during normal plant growth, and in leaves during senescence. Mutants affecting amino acid transport (aap6, aap3, prot1 and gat1), γ‐aminobutyric acid levels (pop2) and senescence/defence (cpr5‐2) were analysed.BABA was found to accumulate only locally after bacterial or fungal infection, with no detectable increase in non‐infected systemic plant parts. In leaves, BABA content increased during natural and induced senescence. Reproductive organs had the highest levels of BABA, and the mutant cpr5‐2 produced constitutively high levels of BABA.Synthetic BABA is highly mobile in the receiving plant, whereas endogenous BABA appears to be produced and accumulated locally in a tissue‐specific way. We discuss a possible role for BABA in age‐related resistance and propose a comprehensive model for endogenous and synthetic BABA. [ABSTRACT FROM AUTHOR]

Resistance (R) genes against plant pathogens often have age-related resistance (ARR) effects. However, the mechanism involved in this phenomenon remains unknown. In this paper, Solanum lycopersicum ‘CLN2037B’ and S. pimpinellifolium ‘L3708’ harboring the Ph-3 gene, as well as S. habrochaites ‘LA2099’, ‘LA1777’ and ‘LA1033’ harboring quantitative trait loci (QTLs), were tested to investigate age-related resistance against late blight (LB; caused by Phytophthora infestans) in the three-leaf stage of the plants. The results demonstrated that the QTL-related LB resistance showed the same age-related resistance as the Ph-3-mediated resistance at the six- and nine-leaf stages compared with the three-leaf stage. This indicated that there is a common defense mechanism in tomatoes against P. infestans via ARR. In addition, we combined ethylene (ET), salicylic acid (SA) and jasmonic acid (JA) mutants with virus-induced gene silencing (VIGS) to study the Ph-3-dependent resistance signaling pathway. The results showed that ethylene and salicylic acid, but not jasmonic acid, are involved in the LB resistance mediated by the Ph-3 gene.

Efforts in improving banana plants that are resistant to the Fusarium wilt-causing Fusarium oxysporum f.sp. cubense tropical race 4 (Foc4) are indispensable. In this study, we developed rapid, space-efficient in vitro bioassay for assessing banana plant resistance to Foc4 using 35 × 150 mm glass test tubes, followed by quantitative and objective analysis of necrosis area and biomass changes as represented by fresh weight changes. Disease resistance screening was conducted based on the necrosis area as quantified using ImageJ software and on biomass gain during in vitro bioassay. In vitro banana plantlets showed age-related resistance during the development of necrosis (p = .034, Kruskal-Wallis test in root and shoot system and p = .027, one-way ANOVA in shoot system only), in which plantlets that were infected at the youngest age (24 weeks' post-initiation) showed the largest necrosis area (up to 46.6%). In addition, plant fresh weight gain in this group (0.233 ± 0.041 g) was higher compared to the gains in older plantlets (0.079 ± 0.117 and 0.009 ± 0.069 g, infected at 28 and 38 weeks' post-initiation, respectively). Overall, for consistent and reliable result, the age of banana plantlet should be taken into consideration in interpreting the result of this in vitro bioassay. [ABSTRACT FROM AUTHOR]

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Botryosphaeria dothidea is one of the most important pathogens of apple trees in China. It causes warts and cankers on shoots and fruit rot. In this study, multi-season experiments were conducted to investigate the seasonal dynamics of B. dothidea infection and symptom development on twigs and fruits of cv. Fuji through spraying and rain-splash inoculations. Fruit were most susceptible to infection from late May to mid-August. The length of the incubation period, i.e. from inoculation to the first lesion was observed, generally decreased with the age of fruit at the time of inoculation. Fruit inoculated in May-June developed visible symptoms from early August onwards, with a peak in early September. However, fruit inoculated in September developed visible symptoms within one week after inoculation. Twigs remained susceptible to infection by conidia from the initial extension stage in early May to late September. New extension shoots were most susceptible from June to mid-August and then became gradually less susceptible over time. When inoculated before the end of August, twigs developed visible lesions within the same season. In contrast, when inoculated late in the season, most lesions became visible during the subsequent season. The incubation period on twigs was shorter for inoculations conducted in June-August, with the shortest being 25 days. These results may contribute to the improvement of the management of this disease. [ABSTRACT FROM AUTHOR]

Vascular phloem loading has long been recognized as an essential step in the establishment of a systemic virus infection. In this study, an interaction between the replication protein of tobacco mosaic virus (TMV) and phloem-specific auxin/indole acetic acid (Aux/IAA) transcriptional regulators was found to modulate virus phloem loading in an age-dependent manner. Promoter expression studies show that in mature tissues TMV 126/183-kDa-interacting Aux/IAAs predominantly express and accumulate within the nuclei of phloem companion cells (CCs). Furthermore, CC Aux/IAA nuclear localization is disrupted upon infection with an interacting virus. In situ analysis of virus spread shows that the inability to disrupt Aux/IAA CC nuclear localization correlates with a reduced ability to load into the vascular tissue. Subsequent systemic movement assays also demonstrate that a virus capable of disrupting Aux/IAA localization is significantly more competitive at moving out of older plant tissues than a noninteracting virus. Similarly, CC expression and overaccumulation of a degradation- resistant Aux/IAA-interacting protein was found to inhibit TMV accumulation and phloem loading selectively in flowering plants. Transcriptional expression studies demonstrate a role for Aux/IAA-interacting proteins in the regulation of salicylic and jasmonic acid host defense responses as well as virus-specific movement factors, including pectin methylesterase, that are involved in regulating plasmodesmata size-exclusion limits and promoting virus cell-to-cell movement. Combined, these findings indicate that TMV directs the reprogramming of auxin-regulated gene expression within the vascular phloem of mature tissues as a means to enhance phloem loading and systemic spread. [ABSTRACT FROM AUTHOR]

Although developmentally regulated disease resistance has been observed in a variety of plant-pathogen interactions, the molecular basis of this phenomenon is not well understood. Arabidopsis thaliana ecotype Columbia-0 (Col-0) expresses a developmentally regulated resistance to Hyaloperonospora parasitica isolate Emco5. Col-0 seedlings support profuse mycelial growth and asexual spore formation in the cotyledons. In contrast, Emco5 growth and reproducetion is dramatically (but not completely) restricted in the first set of true leaves. Subsequent leaves exhibit progresssively increased resistance. This adult resistance is strongly suppressed by expression of the salicylic acid-degrading transgene NahG and by loss-of-function mutations in the defense-response regulators PAD4, NDR1, RAR1, PBS3 and NPR1. In contrast to Col-0, the Wassilewskija-0 (Ws-0) ecotype supports profuse growth of Emco5 at all stages of development. Gene-dosage experiments and segregation patterns indicate that adult susceptibility in Ws-0 is incomepletely dominant to adult resistance in Col-0. Genetic mapping in a Col × Ws F2 population revealed a major locus on the bottom arm of chromosome 5, which we named RPP31. Analysis of T-DNA insertion lines indicated that the Columbia allele of RPP8, though tightly linked to RPP31, is not necessary for adult resistance.

The impact of age-related resistance on the regulation of population dynamics of adult Trichuris suis was investigated in an experimental pig model. Helminth-naive pigs varying in age from five weeks to four years were infected with T. suis to determine susceptibility to infection. Sows had a significantly lower establishment of adult T. suis worms compared with weaner pigs. Adult worm populations were highly overdispersed in both sows and grower pigs contrasted by a more even distribution among weaner pigs. Sows had significantly lower worm fecundities compared to weaner and grower pigs; T. suis from grower pigs, in turn, had reduced fecundity compared to worms in weaner pigs. In conclusion, we provide the first controlled experimental evidence that age-related resistance to T. suis occurs in pigs.

Peroxidases (POXs) are actively synthesised under stress conditions and induced by biotic/abiotic elicitors. Their age-regulated expression in plants has been a matter of investigation during recent times. The present study focuses on studying the expression of POX at different stages of growth and variation in its inducibility by aqueous extract ofAzadirachta indica(neem) fruits. Tomato plants at 6, 8, 10 and 12 weeks were chosen for the study. The third nodal leaf of each plant was treated with neem fruit extract alone or in combination withPseudomonas syringaepv.tomato. Sampling was performed at an interval of 24 h up to five days and after two weeks of treatment, from both the treated and distal untreated nodes of the plants. POX activity and its isoforms were analysed. The results demonstrated that POX expression and its inducibility by the biotic inducer (neem fruit extract) varies with age of the plant. [ABSTRACT FROM AUTHOR]

In Arabidopsis, much of what we know about the phytohormone salicylic acid (SA) and its role in plant defense comes from experiments using young plants. We are interested in understanding why young plants are susceptible to virulent strains of Pseudomonas syringae, while mature plants exhibit a robust defense response known as age-related resistance (ARR). SA-mediated signaling is important for defense in young plants, however, ARR occurs independently of the defense regulators NPR1 and WHY1. Furthermore, intercellular SA accumulation is an important component of ARR, and intercellular washing fluids from ARR-competent plants exhibit antibacterial activity, suggesting that SA acts as an antimicrobial agent in the intercellular space. Young plants accumulate both intracellular and intercellular SA during PAMP- and effector-triggered immunity, however, virulent P. syringae promotes susceptibility by suppressing SA accumulation using the phytotoxin coronatine. Here we outline the hypothesis that mature, ARR-competent Arabidopsis alleviates coronatine-mediated suppression of SA accumulation. We also explore the role of SA in other mature-plant processes such as flowering and senescence, and discuss their potential impact on ARR. [ABSTRACT FROM AUTHOR]

Age-related resistance (ARR) is a plant defense response characterized by enhanced resistance to certain pathogens in mature plants relative to young plants. In Arabidopsis thaliana the transition to flowering is associated with ARR competence, suggesting that this developmental event is the switch that initiates ARR competence in mature plants (Rusterucci et al. in Physiol Mol Plant Pathol 66:222-231, ). The association of ARR and the floral transition was examined using flowering-time mutants and photoperiod-induced flowering to separate flowering from other developmental events that occur as plants age. Under short-day conditions, late-flowering plant lines ld- 1 ( luminidependens- 1), soc1- 2 ( suppressor of overexpression of co 1- 2), and FRI ( FRIGIDA) displayed ARR before the transition to flowering occurred. Early-flowering svp- 31, svp- 32 ( short vegetative phase), and Ws-2 were ARR-defective, whereas early-flowering tfl1- 14 ( terminal flower 1- 14) displayed ARR at the same time as Col-0. While svp- 31, svp- 32 and Ws-2 produced few rosette leaves, tfl1- 14 produced a rosette leaf number similar to Col-0, suggesting that the development of a minimum number of rosette leaves is necessary to initiate ARR competence under short-day conditions. Photoperiod-induced transient expression of FT ( FLOWERING LOCUS T) caused precocious flowering in short-day-grown Col-0 but this was not associated with ARR competence. Under long-day conditions co- 9 ( constans- 9) mutants did not flower but displayed an ARR response at the same time as Col-0. This study suggests that SVP is required for the ARR response and that the floral transition is not the developmental event that regulates ARR competence. [ABSTRACT FROM AUTHOR]

Wheat cultivar Xingzi 9104 (XZ) possesses adult plant resistance (APR) to stripe rust caused by Puccinia striiformis f. sp. tritici ( Pst). In this study, histological and cytological experiments were conducted to elucidate the mechanisms of APR in XZ. The results of leaf inoculation experiments indicated that APR was initiated at the tillering stage, gradually increased as the plant aged and highly expressed after boot stage. The histology and oxidative burst in infected leaves of plants at seedling, tillering and boot stages were examined using light microscopic and histochemical methods. Subcellular changes in the host-pathogen interactions during the seedling and boot stages were analyzed by transmission electron microscopy. The results showed that haustorium formation was retarded in the adult plants and that the differentiation of secondary intercellular hyphae was significantly inhibited, which decreased the development of microcolonies in the adult plants, especially in plants of boot stage. The expression of APR to stipe rust during wheat development was clearly associated with extensive hypersensitive cell death of host cells and localized production of reactive oxygen species, which coincided with the restriction of fungal growth in infection sites in adult plants. At the same time, cell wall-related resistance in adult plants prevented ingression of haustorial mother cells into plant cells. Haustorium encasement was coincident with malformation or death of haustoria. The results provide useful information for further determination of mechanisms of wheat APR to stripe rust. Key message The expression of APR to stipe rust in wheat cultivar Xingzi 9104 (XZ) was clearly associated with extensive hypersensitive cell death of host cells and the localized production of reactive oxygen species. [ABSTRACT FROM AUTHOR]

Abstract: Sulfated laminarin (PS3) has previously been shown to induce resistance of grapevine leaves against the oomycete Plasmopara viticola, the causal agent of grape downy mildew. Here, we observed that the level of PS3-induced resistance (PS3-IR) was higher in the adult leaf (in position P3) than in the younger, not fully expanded leaf (in position P1, located above P3). By investigating grapevine defense reactions upon PS3 treatment and inoculation, we found that the production of H2O2, of phytoalexins, and the deposition of phenolics were more abundant in P3 than in P1 leaves. In addition, PS3 significantly reduced stomatal colonization by zoospores only in P3 leaves. Thus, the capacity of an adult leaf to express a higher level of defense reactions during PS3-IR may partly explain why it exhibits a more elevated resistance when compared to a young leaf, still in growth. These findings have likely practical consequences in induced resistance application. [Copyright &y& Elsevier]

Powdery mildew caused by an obligate biotrophic fungus Erysiphe necator (synonym Uncinula necator) is the most economically important disease of grapevines. Most widely grown grape cultivars are highly susceptible to E. necator, because they are derived from Vitis vinifera, a species which was not exposed to this pathogen during its evolution. In this study we investigated germinating of grapevine powdery mildew on two susceptible and resistant grapevine genotypes as well as ontogenic resistance in vegetative tissues of Cabernet sauvignon and Arabidopsis thaliana with different age. Conidia germinated and appressorium and haustorium appeared during 2-12 hpi in both genotypes. The primary hypha developed 12 hpi in both genotypes however; yellow deposits could be seen surround epidermal cells 12 hpi just in resistant genotype. Development of primary hypha continued up to 24 hpi in susceptible Cabernet sauvignon, however, 24 hpi the hypersensitive reaction (HR) happened in resistant genotype and blocked secondary hypha development, but not in Cabernet sauvignon. By increased in physiological age related to ontogenic resistance the penetration efficiency of fungi in Cabernet sauvignon and Arabidopsis thaliana reduced. [ABSTRACT FROM AUTHOR]

Abstract: As Arabidopsis matures it becomes resistant to virulent Pseudomonas syringae pv. tomato (Pst), a defense response known as Age-Related Resistance (ARR). The contribution of two NAC transcription factors (ANAC055 and ANAC092) and jasmonic acid/ethylene (JA/ET) signaling to ARR was examined by comparing Pst growth in wild-type plants, nac mutants, an ANAC092-overexpressing line, lox2, and ein2-1. PDF1.2 expression and anac055anac092 double mutant analysis suggests that ANAC055 and ANAC092 play non-redundant roles in ARR. Additionally, ANAC092 contributes to the initiation of flowering in short day-grown plants. ANAC055 and ANAC092 expression was reduced in partially ARR-defective ein2-1 suggesting that regulation of ANAC055 and ANAC092 by EIN2 contributes to ARR. [Copyright &y& Elsevier]

Resource sharing between connected ramets can be advantageous for clonal plants. However, widespread vascular integration bears the risks of enhanced internal pathogen spread, which may be one of the most prominent disadvantages of clonal growth. In this paper we analyzed patterns of internal virus spread in ramet groups of the stoloniferous herb L. (white clover) and investigated the effect of leaf ontogeny on intraclonal disease development. We inoculated single leaves of T. repens with White clover mosaic virus and analyzed the infection status of ramets at different distances from the point of infection and in leaves from different developmental stages. White clover mosaic virus infected all young developing plant parts positioned on basal branches or on the main stolon. Leaf ontogeny strongly affected disease development, and fully mature leaves on the main stolon remained virus free. The pattern of plant-internal virus spread was not affected by heterogeneous light conditions. Despite the well-described advantages of physiological integration, our data suggest that clonal integration may lead to negative selection pressures on clonal growth in pathogen-prone environments. [ABSTRACT FROM AUTHOR]

Abstract: The oomycete pathogen, Phytophthora infestans, is the causal agent of potato late blight, which is one of the most destructive and economically important plant diseases. We investigated the interaction between P. infestans and Solanaceous model plant Nicotiana benthamiana. Mature N. benthamiana plants were resistant to 8 isolates of P. infestans, whereas relatively young plants were susceptible to all isolates. Analysis with virus-induced gene silencing (VIGS) indicated that NbSGT1 and NbHSP90, genes essential for the function of R proteins, are required for the resistance of N. benthamiana to P. infestans. NbSGT1 was also required for the production of reactive oxygen species (ROS), hypersensitive cell death and expression of NbEAS, a gene for phytoalexin biosynthesis, induced by INF1, a secretory protein derived from P. infestans. These results suggested that N. benthamiana possibly possesses a broad-spectrum R protein against P. infestans, which requires an SGT1/HSP90-dependent mechanism, for the recognition of a conserved molecular pattern of P. infestans. [Copyright &y& Elsevier]

Victoria blight of oats caused by the fungus Cochliobolus victoriae is of distinct interest due to the link between Victoria blight susceptibility and crown rust resistance . C. victoriae-susceptible oats were introduced into the USA as a source of the Pc2 gene for resistance to the crown rust fungus Puccinia coronata. A dominant gene ( Vb) in these oats was found to condition susceptibility to Victoria blight disease and sensitivity to the C. victoriae toxin called victorin. Numerous genetic approaches to separate Vb from Pc2 have failed, suggesting that Pc2 and Vb share identity. Because Victoria blight has only been described in allohexaploid oat, which has a poorly characterized genome of 11,300 Mb, molecular genetic investigations of Vb in oat are not practical. Previously we identified a presumed Vb ortholog in Arabidopsis, called LOV. LOV confers victorin sensitivity and susceptibility to C. victoriae, and encodes a coil-coil-nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR) protein. Analysis of cereal DNA databases reveals a large array of CC-NBS-LRR genes, but no obvious LOV ortholog. Identifying a cereal ortholog of LOV will require identification and subsequent mapping of victorin sensitivity in a genetically tractable cereal plant. In this work, we surveyed barley for victorin sensitivity and identified adult-onset sensitivity to victorin in eight barley accessions. Evaluation of a doubled haploid (DH) population derived from the cross of sensitive × insensitive parents revealed a single quantitative trait locus (QTL) for victorin sensitivity in a resistance-gene-rich region on the short arm of chromosome 1H. Furthermore, enhanced victorin sensitivity observed in some DH lines suggests a background-dependent enhancement of victorin sensitivity. [ABSTRACT FROM AUTHOR]

We investigated variations in the level and composition of volatiles emitted by tomato leaves at different ages. Our focus also included their antifungal properties and responses to chitosan oligosaccharide. Based on leaf position, the release of volatiles decreased over time. Young leaves produced high levels of C6-aldehyde, which is mainly composed of hexenal, while the volatiles emitted by more mature leaves largely comprised terpenes, particularly β-phellandrene and caryophyllane. In young upper leaves, the main components (up to 86% of the total) were hexenal, β-phellandrene, and caryophyllane. Their levels decreased steadily over time, from 386.3 μg g−1 fresh weight (FW) in young leaves to 113.2 μg g−1 FW in old tissues. Volatiles emitted from young leaves exhibited the best antifungal activity against spore germination and hyphal growth by Botrytis cinerea and Fusarium oxysporum. Leaves became more susceptible to oligosaccharide treatment with increasing age. When young tissues were exposed to chitosan, we found declines in both the quantity of volatiles and their ability to inhibit fungal growth. Compared with the control, the amount of volatiles from young tissues was 88.4% lower after such treatment. In contrast, contents of volatiles from old and adult leaves were dramatically increased by chitosan oligosaccharide. Likewise, their inhibitory effect was significantly enhanced. Therefore, our results suggest that these volatiles are responsible for antifungal activity and may play a role in age-related resistance by tomato. [ABSTRACT FROM AUTHOR]

ABSTRACT Tomato spotted wilt virus (family Bun yaviridae, genus Tospovirus, TSWV) causes annual economic losses in pepper, Capsicum annuum L., across the southern United States and is transmitted by several species of thrips, including the tobacco thrips, Frankliniella fusca (Hinds). Reduced virus transmission and symptom severity as plant age increases is known as mature-plant resistance, TSWV transmission to pepper plants was examined in three and four age classes in field and greenhouse trials, respectively. In the field trial, 'Camelot' bell pepper plants were exposed to potentially viruliferous F. fusca 37, 51, or 65 d postsowing. Two greenhouse trials of Camelot bell and one trial each of 'Bounty' and 'Pageant' banana pepper plants were exposed to potentially viruliferous F.fiisca, 43,57,71, or 85; 48,62,75, or 90; 42,56,70, or 84; and 43,57,71, or 85 d postsowing, respectively. Linear and hyperbolic regressions of percentage of infected plants per block on days postsowing indicated mature-plant resistance in all trials. All models were significant, but hyperbolic curves better fit the data than linear models. Hyperbolic models were used to calculate the number of days posttransplant at which a 50% decrease from the predicted percentage of infected plants at transplant age (42 d postsowing) was expected. This was referred to as days posttransplant-50 (DPT[sub50]). DPT[sub50] occurred within 9 days posttransplant age for all trials, indicating that early TSVVV management in pepper is critical. [ABSTRACT FROM AUTHOR]

Berries of grapevine (Vitis spp.) have a limited window of susceptibility to Uncinula necator, the causal agent of grapevine powdery mildew, until the onset of ontogenic resistance approximately 2 to 3 weeks postbloom. This phenomenon has been demonstrated in several cultivars of V. vinifera and in V. labruscana 'Concord', which all exhibited a similar duration of susceptibility. To identify genetic variation for ontogenic resistance, we screened a diverse collection of Vitis species and interspecific hybrids maintained in the USDA-ARS cold-hardy Vitis germplasm collection in Geneva, NY. Of the 79 genotypes whose fruit clusters were screened for susceptibility to powdery mildew under field conditions, 50 exhibited a high level of constitutive resistance to powdery mildew and did not develop more than trace levels of disease when inoculated, irrespective of the stage of berry development at inoculation. Twenty-four genotypes exhibited a significant gain of resistance as berries aged. This ontogenic resistance was conserved across four species and several interspecific hybrids of Vitis spp., although the timing of the onset of ontogenic resistance varied by genotype. The mechanism of ontogenic resistance was examined for four genotypes. Similar to previous studies, ontogenic resistance greatly reduced the incidence of successful penetration. Despite the broad conservation of ontogenic resistance across species, one genotype (V. rupestris 'R-65-44') remained susceptible past the onset of ripening, over 1 month later than reported previously for V. vinifera and V. labruscana. Variation in the resistance phenotype was observed among the rachis, pedicels, and berries within clusters of the majority of genotypes studied. The genetic variation in ontogenic resistance, in particular the discovery of a genotype in which berries remain susceptible as they mature, will facilitate further study of the inheritance and molecular basis of ontogenic resistance. [ABSTRACT FROM AUTHOR]

Abstract: As plants mature it has been observed that some become more resistant to normally virulent pathogens. The ability to manifest the Age-Related Resistance (ARR) response in Arabidopsis to Pseudomonas syringae pathovars tomato (Pst) coincided with the transition to flowering in plants both delayed and accelerated in the transition to flowering. ARR was also associated with a change in PR-1 gene expression, such that young plants expressed PR-1 abundantly at 3 days post inoculation (dpi) while mature plants expressed much less. The Arabidopsis ARR response requires SA accumulation via isochorismate synthase (ICS1) . ICS1 was expressed one dpi with virulent and avirulent Pst in both young and mature plants. The ARR response was also effective versus avirulent Pst providing an additional 4-fold limitation in bacterial growth. Arabidopsis ARR was found to be ineffective against two necrotrophs, Erwinia carotovora subspecies carotovora (bacterium) and Botrytis cinerea (fungus) and one obligate biotroph, Erysiphe cichoracearum (fungus). However, mature wild type, SA-deficient sid2 and NahG plants supported little growth of the obligate biotrophic oomycete, Peronospora parasitica. Therefore ARR to P. parasitica appears to be SA-independent, however the level of ARR resistance was somewhat reduced in these mutants in some experiments. Thus, there may be numerous defence pathways that contribute to adult plant resistance in Arabidopsis. [Copyright &y& Elsevier]

Abstract: As Arabidopsis plants mature, they develop age-related resistance (ARR) to virulent Pseudomonas syringae. As for other defense responses, salicylic acid (SA) accumulation is required for ARR [Kus JV, Zaton K, Sarkar R, Cameron RK. Age-related resistance in Arabidopsis is a developmentally regulated defense response to P. syringae. Plant Cell 2002;14:479–90]. SA levels in the intercellular space increased during ARR and correlated in some experiments with anti-bacterial activity detection in intercellular washing fluids. Growth of Pseudomonas in culture was inhibited by 1mM SA, providing support for an anti-microbial role for SA during ARR. Application of SA to the intercellular space rescued the ARR-defective mutant sid2, but not the SA-hydrolyzing transgenic line, NahG. The protection afforded by SA application in sid2 was observed only while SA levels remained elevated in the intercellular space. Destruction of SA in the intercellular space, by salicylate hydroxylase application, reduced the ARR response in wild type plants. These results strongly suggest that SA accumulation in the intercellular space is critical for manifestation of ARR. [Copyright &y& Elsevier]