Affect Plant Resistance Research Articles

Micro- and Macromorphological Features of Five Crambe Species Introduced in the M.M. Gryshko National Botanical Garden Nas of Ukraine

Objective: The aim of the study was to establish the micro- and macromorphological features of vegetative and generative organs of plants of species of the genus Crambe, depending on the specific characteristics of the introduction to the M.M. Gryshko National Botanical Garden NAS of Ukraine. Method: The study of vegetative and generative organs was performed by dissection. Exploration and photo-fixation of the microstructure and microsculpture of their surfaces were performed using а light USB microscope SIGETA Expert 10-300x 5.0Mpx, as well as a digital SLR camera Canon 400 D. In order to characterize vegetative and generative organs “Atlases on the Descriptive Morphology of Higher Plants” was used. The material for studying the anatomical features of cross-sections of petioles observed through an electric microscope was taken from the central part of petioles. Results and Discussion: The peculiarities of morphological structure of vegetative and generative organs, anatomical structure of leaves, micromorphology of leaf surface, microsculpture of fruit and seeds of plants of species of the genus Crambe under conditions of introduction have been established. Micromorphological and anatomical studies have revealed a number of traits that affect plant resistance to environmental conditions. Variations in density and nature of pubescence of leaves and stems in different species of the genus Crambe indicate their high adaptive potential. Conclusions: Thus, for the first time the micro- and macromorphological features of vegetative and generative organs associated with the resistance of plants of species of the genus Crambe to environmental conditions were established under the conditions of introduction at M.M. Gryshko National Botanic Garden of National Academy of Science of Ukraine. The plants have been divided into groups according to a range of micromorphological features, which can be further used in breeding and genetic work for the purpose of selecting economically valuable plant species to enrich phytocenoses in Ukraine.

Propagation through seed or somatic embryogenesis: comparing the effects of two methods and methyl jasmonate treatment on Norway spruce resistance to Heterobasidion infection

The clonal propagation method somatic embryogenesis (SE) has been shown to affect plant resistance to an insect pest. In a field trial, Norway spruce SE-plants (emblings) experienced less damage by the bark-chewing pine weevil compared to seedlings propagated through seeds from the same mother tree. Moreover, if emblings were treated with the defense-inducing hormone methyl jasmonate (MeJA), their resistance became much greater compared to the effects of SE and MeJA alone. Thus, we evaluated in a full factorial design if propagation method (seed or SE) and MeJA treatment (treated or not) can affect Norway spruce resistance to infection by the fungal pathogen Heterobasidion parviporum. Emblings and seedlings were half-sibs originating from four different Norway spruce families. We found that emblings and seedlings exhibited similar fungal lesion lengths (LL) and sapwood growth (SWG) in a constitutive state (no MeJA). Once treated, seedlings exhibited a 26% and 28% reduction in LL and SWG growth respectively, in line with previous studies. For emblings, it was the opposite. MeJA increased LL and SWG by 41% and 16% respectively. This is unexpected given the genetic relatedness of the material, and the previously documented effects of SE. It is possible that SE is causing changes in Norway spruce resistance that are effective against insects, but not pathogens. Also, MeJA treatment may be affecting embling terpene composition in ways that benefit fungal growth, as suggested from separate experiments. Further studies are needed to uncover the mechanisms behind the increased susceptibility of Norway spruce emblings to fungal infection.

Exogenous Indole-3-Acetic Acid Suppresses Rice Infection of Magnaporthe oryzae by Affecting Plant Resistance and Fungal Growth.

Auxin is an important phytohormone that regulates diverse biologic processes, including plant growth and immunity. Indole-3-acetic acid (IAA), known as one of the main forms of auxin, is able to activate plant immunity. However, it is unknown whether IAA enhances plant resistance and/or suppresses the growth of the fungal pathogen Magnaporthe oryzae. Here, we found that IAA could induce expression levels of pathogenesis-related genes to enhance disease resistance and could control the development of blast disease through inhibiting M. oryzae infection. Exogenous IAA suppressed mycelial growth and delayed spore germination by inhibiting fungal endogenous IAA biosynthesis and impairing redox homeostasis, respectively. When applied to a field test, two IAA analogues, 1-naphthaleneacetic acid and 2,4-dichlorophenoxy acetic acid, can effectively control rice blast disease. Our study advances the understanding of IAA in controlling rice blast disease through suppressing pathogen growth and enhancing plant resistance.

Adaptations to water gradient in three Rorippa plant species correspond with plant resistance against insect herbivory under drought and waterlogged conditions

Abstract Plants live in environments where they are constantly, and often simultaneously, exposed to different types of biotic and abiotic stress, such as insect herbivory and water availability. How plants are adapted to abiotic conditions may determine how a surplus or shortage of water affects plant resistance to insect herbivory. Moreover, this effect may vary depending on the feeding mode of the herbivore. We explored how three closely related Rorippa plant species that vary in adaptations to different water levels, resist herbivory by four different insects (aphids: Myzus persicae, Lipaphis erysimi, and caterpillars: Pieris brassicae, Plutella xylostella) under waterlogging or drought conditions. We hypothesized that plants that are differently adapted to water availability will be disparately affected by water availability in their resistance to insect herbivory. On the semi‐aquatic plant species Rorippa amphibia, both aphid species reached a larger colony size under drought conditions. This indicates that R. amphibia was compromised in resistance to aphid feeding when under drought conditions, to which it is less well adapted. Water conditions did not affect aphid performance on the flood‐plain species Rorippa palustris. On the terrestrial plant species Rorippa sylvestris, aphids performed worse on waterlogged than drought‐treated plants. Neither caterpillar species was significantly affected by the water availability of their food plant. Our findings suggest that water availability can have distinct effects on plant–insect interactions. We propose that plant adaptations to water conditions can be a major predictor towards explaining the variation of effects that water availability can have on plant–insect interactions.

High ultraviolet-B sensitivity due to lower CPD photolyase activity is needed for biotic stress response to the rice blast fungus, Magnaporthe oryzae

Sensitivity to ultraviolet-B (UVB, 280–315 nm) radiation varies widely among rice (Oryza sativa) cultivars due to differences in the activity of cyclobutane pyrimidines dimer (CPD) photolyase. Interestingly, cultivars with high UVB sensitivity and low CPD photolyase activity have been domesticated in tropical areas with high UVB radiation. Here, we investigated how differences in CPD photolyase activity affect plant resistance to the rice blast fungus, Magnaporthe oryzae, which is one of the other major stresses. We used Asian and African rice cultivars and transgenic lines with different CPD photolyase activities to evaluate the interaction effects of CPD photolyase activity on resistance to M. oryzae. In UVB-resistant rice plants overexpressing CPD photolyase, 12 h of low-dose UVB (0.4 W m−2) pretreatment enhanced sensitivity to M. oryzae. In contrast, UVB-sensitive rice (transgenic rice with antisense CPD photolyase, A-S; and rice cultivars with low CPD photolyase activity) showed resistance to M. oryzae. Several defense-related genes were upregulated in UVB-sensitive rice compared to UVB-resistant rice. UVB-pretreated A-S plants showed decreased multicellular infection and robust accumulation of reactive oxygen species. High UVB-induced CPD accumulation promoted defense responses and cross-protection mechanisms against rice blast disease. This may indicate a trade-off between high UVB sensitivity and biotic stress tolerance in tropical rice cultivars.Graphical

Cold stress triggers freezing tolerance in wheat (Triticum aestivum L.) via hormone regulation and transcription of related genes.

Low temperatures limit the geographic distribution and yield of plants. Hormones play an important role in coordinating the growth and development of plants and their tolerance to low temperatures. However, the mechanisms by which hormones affect plant resistance to extreme cold stress in the natural environment are still unclear. In this study, two winter wheat varieties with different cold resistances, Dn1 and J22, were used to conduct targeted plant hormone metabolome analysis on the tillering nodes of winter wheat at 5 °C, -10 °C and -25 °C using an LC-ESI-MS/MS system. We screened 39 hormones from 88 plant hormone metabolites and constructed a partial regulatory network of auxin, jasmonic acid and cytokinin. GO analysis and enrichment of KEGG pathways in different metabolites showed that the 'plant hormone signal transduction' pathway was the most common. Our study showed that extreme low temperature increased the most levels of auxin, cytokinin and salicylic acid, and decreased levels of jasmonic acid and abscisic acid, and that levels of auxin, jasmonic acid and cytokinin in Dn1 were higher than those in J22. These changes in hormone levels were associated with changes in gene expression in synthesis, catabolism, transport and signal transduction pathways. These results differ from the previous hormone regulation mechanisms, which were mostly obtained at 4 °C. Our results provide a basis for further understanding the molecular mechanisms by which plant endogenous hormones regulate plant freezing stress tolerance.

New insight into the molecular mechanism of miR482/2118 during plant resistance to pathogens.

MicroRNAs (miRNAs), a group of small noncoding RNAs (approximately 20-24 nucleotides), act as essential regulators affecting endogenous gene expression in plants. MiR482/2118 is a unique miRNA superfamily in plants and represses NUCLEOTIDE BINDING SITE-LEUCINE-RICH REPEAT (NBS-LRR) genes to function in plant resistance to pathogens. In addition, over the past several years, it has been found that miR482/2118 not only targets NBS-LRRs but also acts on other molecular mechanisms to affect plant resistance. miR482/2118-5ps, phased small interfering RNAs (phasiRNAs) and long noncoding RNAs (lncRNAs) play important roles in plant disease resistance. This review summarizes the current knowledge of the interactions and links between miR482/2118 and its new interacting molecules, miR482/2118-5p, phasiRNAs and lncRNAs, in plant disease resistance. Here, we aim to provide a comprehensive view describing the new molecular mechanism associated with miR482/2118 in the plant immune system.

Vacuolar processing enzyme positively modulates plant resistance and cell death in response to Phytophthora parasitica infection

Oomycete, particularly Phytophthora species, causes the most devastating crop diseases, such as potato late blight, and threatens the sustainable crop production worldwide. Our previous studies identified Resistance to Phytophthora parasitica 1 (RTP1) as a negative regulator of Arabidopsis resistance to multiple biotrophic pathogens and RTP1 loss-of-function plants displayed rapid cell death and reactive oxygen species (ROS) production during early colonization of P. parasitica. In this study, we aim to decipher the mechanism of RTP1-mediated cell death, and identify a member of vaculoar processing enzymes (VPEs), γVPE, playing a role in rtp1-mediated resistance to P. parasitica and cell death occurrence. Our results showed up-regulation of the expression of γVPE as well as increased VPE/caspase 1-like protease activity in P. parasitica-infected rtp1 mutant plants. Besides, we found that the VPE/caspase 1-like protease activity was required for the cell death occurrence in Arabidopsis plants during the infection of P. parasitica as well as rtp1-mediated resistance to P. parasitica. Further pathogenicity assays on either Arabidopsis γvpe mutant plants or leaves of Nicotiana benthamiana with transient overexpression of γVPE demonstrated γVPE could positively affect plant resistance to P. parasitica. Together, our studies suggest that γVPE might function as an important regulator of plant defense and cell death occurrence in response to P. parasitica infection, and VPE/caspase 1-like protease activity is required for rtp1-mediated resistance to P. parasitica.

The Role of Serendipita indica (Piriformospora indica) in Improving Plant Resistance to Drought and Salinity Stresses.

Simple SummaryEnvironmental stresses are one of the biggest threats to modern agriculture, and climate change has heightened the risks of these stresses in different parts of the world. Among all the environmental stresses, salinity and drought are a severe threat to arid and semi-arid regions of the world, and for a long time, scientists have been searching for ways to reduce the risk of these stresses. In recent decades, solutions have been developed to reduce the risk of environmental stress on plants by identifying beneficial soil microorganisms. This study was conducted to identify morphophysiological and molecular changes of plants in coexistence with Serendipita indica and their impact on drought and salinity stress reduction. The study also has investigated the stressors’ impact on plants and the plants’ mechanisms to cope with them; Furthermore, sharing results with researchers provides a clear path for future research.Plant stress is one of the biggest threats to crops, causing irreparable damage to farmers’ incomes; Therefore, finding suitable, affordable, and practical solutions will help the agricultural economy and prevent the loss of millions of tons of agricultural products. Scientists have taken significant steps toward improving farm productivity in the last few decades by discovering how beneficial soil microorganisms enhance plant resistance to environmental stresses. Among these microorganisms is Serendipita indica, which the benefits of coexisting this fungus with plant roots have been extensively explored in recent years. By investigating fungus specification and its effects on plants’ morphological, physiological, and molecular traits, the present study seeks to understand how Serendipita indica affects plant resistance to salinity and drought conditions. Furthermore, this study attempts to identify the unknown mechanisms of action of the coexistence of Serendipita indica with plants in the face of stress using information from previous studies. Thus, it provides a way for future research to assess the impact of this fungus on tackling environmental stresses and enhancing agricultural productivity.

Effect of the growth regulator ORGANOSTIM on sunflower productivity in the conditions of the central climatic area of the Krasnodar region

The use of growth regulators is an effective element of sunflower cultivation technology due to the ability of this class of substances in small quantities to positively affect plant resistance to stressful conditions and pathogens, increase plant productivity and yield quality. In 2019-2020, we studied the effect of the growth regulator ORGANOSTIM® based on water solutions of taxifolin and crezacin on the yield, seed quality and yield structure indicators of sunflower on leached chernozem of the central climatic area of the Krasnodar region. Presowing seed treatment and foliar spraying at the stages of 6 true leaves development and budding contributed to a significant increase in the number of seeds per head. This resulted in an increase in sunflower seed yield by 5.2-7.3 % and an increase in oil yield by 6.3-8.6 %.

Glutathione contributes to plant defence against parasitic cyst nematodes.

Cyst nematodes (CNs) are an important group of root‐infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l‐γ‐glutamyl‐l‐cysteinyl‐glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate–cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione‐deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione‐mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine‐tuning the balance between the cellular redox environment and the production of compounds related to defence against infection.

A BTB/POZ domain-containing protein negatively regulates plant immunity in Nicotiana benthamiana

Plants have evolved immune systems to fight against pathogens. However, it is still largely unknown how the plant immunity is finely regulated. Here we identified a BTB/POZ domain-containing protein, namely NbBTB, which is predicted to be a member of the ubiquitin E3 ligase complex. The NbBTB expression is downregulated upon the oomycete pathogen Phytophthora parasitica infection. Overexpression of NbBTB in Nicotiana benthamiana promoted plant susceptibility to P. parasitica infection, and silencing NbBTB increased plant resistance to P. parasitica, indicating that NbBTB negatively modulates plant basal defense. Interestingly, overexpressing or silencing NbBTB did not affect plant resistance to two bacterial pathogens Ralstonia solanacearum and Pseudomonas syringae, suggesting that NbBTB is specifically involved in basal defense against oomycete pathogen. Expression of NbBTB suppressed hypersensitive response (HR) triggered by avirulence proteins from both R. sonanacearum and P. infestans, and silencing NbBTB showed the opposite effect, indicating that NbBTB negatively regulates effector-triggered immunity (ETI). Protein accumulation of avirulence effectors in NbBTB-silenced plants was significantly enhanced, suggesting that NbBTB is likely to negatively modulate ETI by affecting effector protein accumulation. Together, our results demonstrated that NbBTB is a negative regulator in both plant basal defense and ETI.

Defense Suppression through Interplant Communication Depends on the Attacking Herbivore Species

In response to herbivory, plants emit volatile compounds that play important roles in plant defense. Herbivore-induced plant volatiles (HIPVs) can deter herbivores, recruit natural enemies, and warn other plants of possible herbivore attack. Following HIPV detection, neighboring plants often respond by enhancing their anti-herbivore defenses, but a recent study found that herbivores can manipulate HIPV-interplant communication for their own benefit and suppress defenses in neighboring plants. Herbivores induce species-specific blends of HIPVs and how these different blends affect the specificity of plant defense responses remains unclear. Here we assessed how HIPVs from zucchini plants (Cucurbita pepo) challenged with different herbivore species affect resistance in neighboring plants. Volatile “emitter” plants were damaged by one of three herbivore species: saltmarsh caterpillars (Estigmene acrea), squash bugs (Anasa tristis), or striped cucumber beetles (Acalymma vittatum), or were left as undamaged controls. Neighboring “receiver” plants were exposed to HIPVs or control volatiles and then challenged by the associated herbivore species. As measures of plant resistance, we quantified herbivore feeding damage and defense-related phytohormones in receivers. We found that the three herbivore species induced different HIPV blends from squash plants. HIPVs induced by saltmarsh caterpillars suppressed defenses in receivers, leading to greater herbivory and lower defense induction compared to controls. In contrast, HIPVs induced by cucumber beetles and squash bugs did not affect plant resistance to subsequent herbivory in receivers. Our study shows that herbivore species identity affects volatile-mediated interplant communication in zucchini, revealing a new example of herbivore defense suppression through volatile cues.

A mutation in the cytokinin receptor CRE1 enhances susceptibility to tobacco mosaic virus in Nicotiana tabacum

Cytokinin (CTK)-mediated pathways play essential roles in plant stress responses. How CTK receptors affect plant resistance to viral pathogens remains unclear. Tobacco mosaic virus [recombinant TMV encoding green fluorescent protein (TMV-GFP)] was used to investigate the role of Nicotiana tabacum CRE1 (CTK receptor 1) in modulating virus susceptibility in N. tabacum. CRE1 deficiency enhanced the susceptibility of N. tabacum to TMV-GFP. The cre1 RNAi mutants showed extensive green florescence and higher transcript levels of the TMV coat protein gene than the wild type (WT) plants. CRE1 deficiency affected the antioxidant response to TMV-GFP, and the RNAi mutants had depressed antioxidant enzyme activities compared to the WT plants under virus infection. In addition, endogenous salicylic acid (SA) accumulation and the expression levels of SA pathway-related defence genes induced by TMV-GFP were significantly repressed in the RNAi mutants compared with the WT plants. Furthermore, the presence of exogenous CTK could only partially reduce the susceptibility of tobacco to TMV caused by CRE1 deficiency. Taken together, these results suggest that CRE1 plays a positive role in the tobacco defence response to the virus and is required for the induction and development of complete defence responses.

MicroRNA319a regulates plant resistance to Sclerotinia stem rot.

MicroRNA319a (miR319a) controls cell division arrest in plant leaves by inhibiting the expression of TCP (TEOSINTE BRANCHED 1/CYCLOIDEA/PCF) family genes. However, it is unclear whether miR319a influences infection by necrotrophic pathogens and host susceptibility. In this study, we revealed that miR319a affects plant resistance to stem rot disease caused by Sclerotinia sclerotiorum. In Brassica rapa plants infected with S. sclerotiorum, miR319a levels increased while the expression levels of several BraTCP genes significantly decreased compared with those of uninfected plants. Overexpression of BraMIR319a in B. rapa increased the susceptibility of the plants to S. sclerotiorum and aggravated stem rot disease, whereas overexpression of BraTCP4-1 promoted plant resistance. RNA sequencing data revealed a potential relationship between miR319a and pathogen-related WRKY genes. Chromatin immunoprecipitation, electrophoretic mobility shift, and reporter transaction assays showed that BraTCP4-1 could bind to the promoters of WRKY75, WRKY70, and WRKY33 and directly activate these pathogen-related genes. Moreover, the expression levels of WRKY75, WRKY70, and WRKY33 in plants overexpressing BraMIR319a decreased significantly, whereas those of plants overexpressing BraTCP4-1 increased significantly, relative to the wild type. These results suggest that miR319a and its target gene BraTCP4 control stem rot resistance through pathways of WRKY genes.

Insect species richness affects plant responses to multi-herbivore attack.

Summary Plants are often attacked by multiple insect herbivores. How plants deal with an increasing richness of attackers from a single or multiple feeding guilds is poorly understood.We subjected black mustard (Brassica nigra) plants to 51 treatments representing attack by an increasing species richness (one, two or four species) of either phloem feeders, leaf chewers, or a mix of both feeding guilds when keeping total density of attackers constant and studied how this affects plant resistance to subsequent attack by caterpillars of the diamondback moth (Plutella xylostella).Increased richness in phloem‐feeding attackers compromised resistance to P. xylostella. By contrast, leaf chewers induced a stronger resistance to subsequent attack by caterpillars of P. xylostella while species richness did not play a significant role for chewing herbivore induced responses. Attack by a mix of herbivores from different feeding guilds resulted in plant resistance similar to resistance levels of plants that were not previously exposed to herbivory.We conclude that B. nigra plants channel their defence responses stronger towards a feeding‐guild specific response when under multi‐species attack by herbivores of the same feeding guild, but integrate responses when simultaneously confronted with a mix of herbivores from different feeding guilds.

R2R3-MYB Transcription Factor MdMYB73 Confers Increased Resistance to the Fungal Pathogen Botryosphaeria dothidea in Apples via the Salicylic Acid Pathway.

MYB transcription factors (TFs) participate in many biological processes. However, the molecular mechanisms by which MYB TFs affect plant resistance to apple ring rot remain poorly understood. Here, the R2R3-MYB gene MdMYB73 was cloned from "Royal Gala" apples and functionally characterized as a positive regulator of the defense response to Botryosphaeria dothidea. qRT-PCR and GUS staining demonstrated that MdMYB73 was strongly induced in apple fruits and transgenic calli after inoculation with B. dothidea. MdMYB73 overexpression improved resistance to B. dothidea in apple calli and fruits, while MdMYB73 suppression weakened. Increased resistance to B. dothidea was also observed in MdMYB73-expressing Arabidopsis thaliana. Interestingly, salicylic acid (SA) contents and the expression levels of genes related with SA synthesis and signaling were greater in MdMYB73-overexpressing plant materials compared to wild-type controls after inoculation, suggesting that MdMYB73 might enhance resistance to B. dothidea via the SA pathway. Finally, we discovered that MdMYB73 interacts with MdWRKY31, a positive regulator of B. dothidea. Together, MdWRKY31 and MdMYB73 enhanced B. dothidea resistance in apples. Our results clarify the mechanisms by which MdMYB73 improves resistance to B. dothidea and suggest that resistance may be affected by regulating the SA pathway.

Effect of water stress on glucosinolate content of Brassica carinata and performance of Brevicoryne brassicae and Myzus persicae

Drought-related changes in plant chemical composition affect plant resistance to insect herbivores. Ethiopian mustard (Gomenzer) Brassica carinata (A) Braun var. Yellow Dodolla was grown under three different water treatments; drought-stressed, well-watered and water-logged conditions to evaluate glucosinolate content and performance of two aphid species, the generalist Myzus persicae (Sulzer) and specialist Brevicoryne brassicae (L.). The analysis of High Performance Liquid Chromatography showed that water stress altered the levels of glucosinolates in (B) carinata plants. Plants cultivated under water-logged showed significantly higher glucosinolate content (2.236 µmol/g) when compared to well-watered (1.307 µmol/g) plants, whereas plants grown under drought-stressed (0.773 µmol/g) showed significantly reduced glucosinolate content after two week stress. B. carinata plants grown under water-logged condition had significantly higher sugar level (785.8 µg/g) followed by well-watered (667.6 µg/g) and drought-stressed (637.9 µg/g) plants after two week stress. Both aphid species reacted differently to water stress-induced change in the host plants. Significantly higher number of B. brassicae was recorded on plants grown under drought-stressed (395 aphids) plants than well-watered (278 aphids) and water-logged plants (179 aphids). Populations of M. persicae were significantly larger on plants grown under water-logged (558 aphids) and followed by well-watered (329 aphids) and drought-stressed plants (193 aphids). Feeding by both aphid B. brassicae and M. persicae increased significantly the level of glucosinolates in B. carinata plants. B. brassicae induced higher amount of glucosinolate content (3.85 µmol/g) when feeding on drought-stressed plants whereas M. persicae induced higher glucosinolate content (3.55 µmol/g) on water-logged plants. Water stressed B. carinata plants resulted to lower glucosinolate content and higher aphid population.

Divergence of defensive cucurbitacins in independent Cucurbita pepo domestication events leads to differences in specialist herbivore preference.

Crop domestication and improvement often concurrently affect plant resistance to pests and production of secondary metabolites, creating challenges for isolating the ecological implications of selection for specific metabolites. Cucurbitacins are bitter triterpenoids with extreme phenotypic differences between Cucurbitaceae lineages, yet we lack integrated models of herbivore preference, cucurbitacin accumulation, and underlying genetic mechanisms. In Cucurbita pepo, we dissected the effect of cotyledon cucurbitacins on preference of a specialist insect pest (Acalymma vittatum) for multiple tissues, assessed genetic loci underlying cucurbitacin accumulation in diverse germplasm and a biparental F2 population (from a cross between two independent domesticates), and characterized quantitative associations between gene expression and metabolites during seedling development. Acalymma vittatum affinity for cotyledons is mediated by cucurbitacins, but other traits contribute to whole-plant resistance. Cotyledon cucurbitacin accumulation was associated with population structure, and our genetic mapping identified a single locus, Bi-4, containing genes relevant to transport and regulation - not biosynthesis - that diverged between lineages. These candidate genes were expressed during seedling development, most prominently a putative secondary metabolite transporter. Taken together, these findings support the testable hypothesis that breeding for plant resistance to insects involves targeting genes for regulation and transport of defensive metabolites, in addition to core biosynthesis genes.

Effect of Temperature on Plant Resistance to Arthropod Pests.

Temperature has a strong influence on the development, survival, and fecundity of herbivorous arthropods, and it plays a key role in regulating the growth and development of their host plants. In addition, temperature affects the production of plant secondary chemicals as well as structural characteristics used for defense against herbivores. Thus, temperature has potentially important implications for host plant resistance. Because temperature directly impacts arthropod pests, both positively and negatively, distinguishing direct effects from indirect effects mediated through host plants poses a challenge for researchers and practitioners. A more comprehensive understanding of how temperature affects plant resistance specifically, and arthropod pests in general, would lead to better predictions of pest populations, and more effective use of plant resistance as a management tactic. Therefore, the goals of this paper are to 1) review and update knowledge about temperature effects on plant resistance, 2) evaluate alternative experimental approaches for separating direct from plant-mediated indirect effects of temperature on pests, including benefits and limitations of each approach, and 3) offer recommendations for future research.