Plant Defense
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Laura O. Marmolejo ◽  
Morgan N. Thompson ◽  
Anjel M. Helms

AbstractIn 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.

2021 ◽  
Vol 11 (18) ◽  
pp. 8710
Irene Dini ◽  
Marica Pascale ◽  
Alessia Staropoli ◽  
Roberta Marra ◽  
Francesco Vinale

Beneficial fungal strains of the genus Trichoderma are used as biofungicides and plant growth promoters. Trichoderma strains promote the activation of plant defense mechanisms of action, including the production of phenolic metabolites. In this work, we analyzed the effects of selected Trichoderma strains (T. asperellum KV906, T. virens GV41, and T. harzianum strains TH1, M10, and T22) and their metabolites (harzianic acid and 6-pentyl-α-pyrone) on drupes of young olive trees (4-year-old) cv. Carolea. This study used the untargeted analysis of drupe metabolome, carried out by LC–MS Q-TOF, to evaluate the phenolics profiles and target metabolomics approach to detect oleuropein and luteolin. The untargeted approach showed significant differences in the number and type of phenolic compounds in olive drupes after Trichoderma applications (by root dipping and drench soil irrigation method) compared to control. The levels of oleuropein (secoiridoid) and luteolin (flavonoid) varied according to the strain or metabolite applied, and in some cases, were less abundant in treated plants than in the control. In general, flavonoids’ levels were influenced more than secoiridoid production. The dissimilar aptitudes of the biological treatments could depend on the selective competence to cooperate with the enzymes involved in producing the secondary metabolites to defend plants by environmental stresses. Our results suggest that using selected fungi of the genus Trichoderma and their metabolites could contribute to selecting the nutraceutical properties of the olive drupe. The use of the metabolites would bring further advantages linked to the dosage in culture and storage.

New Forests ◽  
2021 ◽  
Magdalena Kulczyk-Skrzeszewska ◽  
Barbara Kieliszewska-Rokicka

AbstractPopulus nigra ‘Italica’ (Lombardy poplar) is a breeding cultivar of black poplar, widely used as a street tree or windbreak, often exposed to salinity and limited water availability. Populus roots can develop dual mycorrhizal associations with ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi, and with non-mycorrhizal fungal endophytes (FE). The symbiotic fungi may alleviate the effects of adverse environmental conditions. We investigated the performance (growth and symbiotic associations) of one-year-old Populus nigra ‘Italica’ grown from woody cuttings in soil from natural poplar habitat and subjected to water scarcity and soil salinity (50 mM NaCl, 150 mM NaCl, 250 mM NaCl). With increasing soil salinity, a decrease in the growth parameters of the aboveground parts of the poplar plantlets and their fine roots were found; however, the roots were more resistant to the stress factors analyzed than the shoots. ECMF, AMF, and non-mycorrhizal FE were all tolerant to increased salt levels in the soil, and the ECM abundance was significantly higher under conditions of mild salinity (50 mM NaCl, 150 mM NaCl) compared to the control plants and those treated with 250 mM NaCl. Our results indicated that enhanced soil salinity increased the content of sodium and chlorine in leaves, but did not affect significantly the concentrations potassium, magnesium, calcium, phosphorus, or nitrogen. Significant accumulation of proline in leaves suggest salt stress of P. nigra ‘Italica’ treated with 250 mM NaCl and contribution of proline to the plant defense reactions.

2021 ◽  
Vol 22 (18) ◽  
pp. 10073
Ji-Nam Kang ◽  
Woo-Haeng Lee ◽  
So Youn Won ◽  
Saemin Chang ◽  
Jong-Pil Hong ◽  

Wounds in tissues provide a pathway of entry for pathogenic fungi and bacteria in plants. Plants respond to wounding by regulating the expression of genes involved in their defense mechanisms. To analyze this response, we investigated the defense-related genes induced by wounding in the leaves of Senna tora using RNA sequencing. The genes involved in jasmonate and ethylene biosynthesis were strongly induced by wounding, as were a large number of genes encoding transcription factors such as ERFs, WRKYs, MYBs, bHLHs, and NACs. Wounding induced the expression of genes encoding pathogenesis-related (PR) proteins, such as PR-1, chitinase, thaumatin-like protein, cysteine proteinase inhibitor, PR-10, and plant defensin. Furthermore, wounding led to the induction of genes involved in flavonoid biosynthesis and the accumulation of kaempferol and quercetin in S. tora leaves. All these genes were expressed systemically in leaves distant from the wound site. These results demonstrate that mechanical wounding can lead to a systemic defense response in the Caesalpinioideae, a subfamily of the Leguminosae. In addition, a co-expression analysis of genes induced by wounding provides important information about the interactions between genes involved in plant defense responses.

2021 ◽  
Collin B. Edwards ◽  
Stephen B. Ellner ◽  
Anurag Agrawal

As a general rule, plants defend against herbivores with multiple traits. The defense synergy hypothesis posits that some traits are more potent when co-expressed with others, compared to their independent potency. However, this hypothesis has rarely been tested outside of synergies within a class of particular phytochemicals, and seldom under field conditions. We tested for synergies between multiple defense traits of common milkweed (Asclepias syriaca) by assaying the performance of two specialist herbivores on plants in natural populations. We employed both standard regression and exploratory analysis using a novel application of Random Forests that allowed us to detect synergies between defense traits. In hypothesis testing, we found the first empirical evidence for a previously hypothesized synergy between one pair of co-expressed defense traits (latex and cardenolides), but not another (latex and trichomes). When exploring all potential interactions between pairs of traits we found eight synergies and five antagonisms in predicting herbivore performance. Half of the identified synergies involved carbon, which is the basis of several defenses including chemical and physical barriers to feeding, and also essential nutrients. Our findings suggest that defense synergies could explain co-expression of latex and cardenolides in milkweeds. This synergy may be common among the diverse plant species that employ latex as a defense. Future studies should test carbon-based synergies, which our work suggests are prevalent, as well as the other synergies identified in our exploratory analysis. Our analytic approach provides a general, flexible framework for more broadly discovering and predicting the coexpression of traits through their synergistic function.

HortScience ◽  
2021 ◽  
pp. 1-10
Eduardo Esteves ◽  
Gabriel Maltais-Landry ◽  
Flavia Zambon ◽  
Rhuanito Soranz Ferrarezi ◽  
Davie M. Kadyampakeni

The bacterial disease Huanglongbing (HLB) has drastically reduced citrus production in Florida. Nutrients play an important role in plant defense mechanisms and new approaches to manage the disease with balanced nutrition are emerging. Nutrients like nitrogen (N), calcium (Ca), and magnesium (Mg) could extend the productive life of affected trees, although interactions among these nutrients in HLB-affected citrus trees are still unclear. A 2-year study was established in Florida to determine the response of HLB-affected trees to applications of N, Ca, and Mg. The study was conducted with ‘Valencia’ trees (Citrus sinensis L. Osbeck) on Swingle citrumelo (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) rootstock on a Candler sand. Applications of N at 168, 224 (recommended rate), and 280 kg⋅ha−1 N were used as the main plots. Split-plots consisted of a grower standard treatment receiving only basal Ca (51 kg⋅ha−1) and Mg (56 kg⋅ha−1); supplemental Ca (total Ca inputs: 96 kg⋅ha−1) only; supplemental Mg (total Mg inputs: 101 kg⋅ha−1) only; and supplemental Ca (total Ca inputs: 73.5 kg⋅ha−1) and Mg (total Mg inputs: 78.5 kg⋅ha−1). The following variables were measured: tree size, fruit yield, and juice quality. Although some differences in tree growth among treatments were statistically significant (e.g., greater canopy volume with Mg fertilization at 168 kg⋅ha−1 N), there was no clear and consistent effect of plant nutrition on these variables. Fruit yield was higher with Ca and Mg relative to the grower standard at the lowest N rate in 2020, and there were no other statistically significant differences among treatments. Juice acidity was significantly higher with Mg fertilization relative to other treatments in 2019. As N rates had no significant effect in this study, unlike secondary macronutrients, N rates could potentially be reduced to 168 kg N⋅ha−1 in HLB-affected citrus without affecting vegetative growth, fruit yield, and juice quality. However, this will require optimizing the supply of secondary macronutrients and all other nutrients to develop a balanced nutritional program. Ultimately, the effects of N, Ca, and Mg obtained in this 2-year study should be confirmed with longer-term studies conducted at multiple sites.

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0257392
Muhammad Numan ◽  
Shazia Anwer Bukhari ◽  
Mahmood-ur- Rehman ◽  
Ghulam Mustafa ◽  
Bushra Sadia

Wheat is a major staple food and has been extensively grown around the globe. Sessile nature of plants has exposed them to a lot of biotic and abiotic stresses including fungal pathogen attack. Puccinia graminis f.sp. tritici causes stem rust in the wheat crop and leads to 70% decrease in its production. Pathogenesis-related (PR) proteins provide plants with defense against different fungal pathogens as these proteins have antifungal activities. This study was designed to screen Pakistani wheat varieties for PR2 and PR3 proteins and their in silico characterization. PR2 and PR3 genes were screened and isolated by PCR amplification from wheat variety Chenab-70 and Frontana, respectively. The nucleotide sequences of PR2 and PR3 genes were deposited in GenBank with accession numbers MT303867 and MZ766118, respectively. Physicochemical properties, secondary and tertiary structure predictions, and molecular docking of protein sequences of PR2 and PR3 were performed using different bioinformatics tools and software. PR2 and PR3 genes were identified to encode β–1,3–glucanase and chitinase proteins, respectively. Molecular docking of both PR2 and PR3 proteins with beta-glucan and chitin (i.e. their respective ligands) showed crucial amino acid residues involved in molecular interactions. Conclusively, molecular docking analysis of β–1,3–glucanase and chitinase proteins revealed crucial amino acid residues which are involved in ligand binding and important interactions which might have important role in plant defense against fungal pathogens. Moreover, the active residues in the active sties of these proteins can be identified through mutational studies and resulting information might help understanding how these proteins are involved in plant defense mechanisms.

2021 ◽  
Vol 12 ◽  
Adriana Aranda-Rickert ◽  
Javier Torréns ◽  
Natalia I. Yela ◽  
María Magdalena Brizuela ◽  
Verónica S. Di Stilio

Dioecious plants are obligate outcrossers with separate male and female individuals, which can result in decreased seed set with increasing distance between the sexes. Wind pollination is a common correlate of dioecy, yet combined wind and insect pollination (ambophily) could be advantageous in compensating for decreased pollen flow to isolated females. Dioecious, ambophilous gymnosperms Ephedra (Gnetales) secrete pollination drops (PDs) in female cones that capture airborne pollen and attract ants that feed on them. Plant sugary secretions commonly reward ants in exchange for indirect plant defense against herbivores, and more rarely for pollination. We conducted field experiments to investigate whether ants are pollinators and/or plant defenders of South American Ephedra triandra, and whether their contribution to seed set and seed cone protection varies with distance between female and male plants. We quantified pollen flow in the wind and assessed the effectiveness of ants as pollinators by investigating their relative contribution to seed set, and their visitation rate in female plants at increasing distance from the nearest male. Ants accounted for most insect visits to female cones of E. triandra, where they consumed PDs, and pollen load was larger on bigger ants without reduction in pollen viability. While wind pollination was the main contributor to seed set overall, the relative contribution of ants was distance dependent. Ant contribution to seed set was not significant at shorter distances, yet at the farthest distance from the nearest male (23 m), where 20 times less pollen reached females, ants enhanced seed set by 30% compared to plants depending solely on wind pollination. We found no evidence that ants contribute to plant defense by preventing seed cone damage. Our results suggest that, despite their short-range movements, ants can offset pollen limitation in isolated females of wind-pollinated plants with separate sexes. We propose that ants enhance plant reproductive success via targeted delivery of airborne pollen, through frequent contact with ovule tips while consuming PDs. Our study constitutes the first experimental quantification of distance-dependent contribution of ants to pollination and provides a working hypothesis for ambophily in other dioecious plants lacking pollinator reward in male plants.

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