Responses to larval herbivory in the phenylpropanoid pathway of Ulmus minor are boosted by prior insect egg deposition

Main conclusion Elms, which have received insect eggs as a ‘warning’ of larval herbivory, enhance their anti-herbivore defences by accumulating salicylic acid and amplifying phenylpropanoid-related transcriptional and metabolic responses to hatching larvae. Abstract Plant responses to insect eggs can result in intensified defences against hatching larvae. In annual plants, this egg-mediated effect is known to be associated with changes in leaf phenylpropanoid levels. However, little is known about how trees—long-living, perennial plants—improve their egg-mediated, anti-herbivore defences. The role of phytohormones and the phenylpropanoid pathway in egg-primed anti-herbivore defences of a tree species has until now been left unexplored. Using targeted and untargeted metabolome analyses we studied how the phenylpropanoid pathway of Ulmus minor responds to egg-laying by the elm leaf beetle and subsequent larval feeding. We found that when compared to untreated leaves, kaempferol and quercetin concentrations increased in feeding-damaged leaves with prior egg deposition, but not in feeding-damaged leaves without eggs. PCR analyses revealed that prior insect egg deposition intensified feeding-induced expression of phenylalanine ammonia lyase (PAL), encoding the gateway enzyme of the phenylpropanoid pathway. Salicylic acid (SA) concentrations were higher in egg-treated, feeding-damaged leaves than in egg-free, feeding-damaged leaves, but SA levels did not increase in response to egg deposition alone—in contrast to observations made of Arabidopsis thaliana. Our results indicate that prior egg deposition induces a SA-mediated response in elms to feeding damage. Furthermore, egg deposition boosts phenylpropanoid biosynthesis in subsequently feeding-damaged leaves by enhanced PAL expression, which results in the accumulation of phenylpropanoid derivatives. As such, the elm tree shows similar, yet distinct, responses to insect eggs and larval feeding as the annual model plant A. thaliana.

Priming of Plant Defenses against Ophiostoma novo-ulmi by Elm (Ulmus minor Mill.) Fungal Endophytes

Some fungal endophytes of forest trees are recognized as beneficial symbionts against stresses. In previous works, two elm endophytes from the classes Cystobasidiomycetes and Eurotiomycetes promoted host resistance to abiotic stress, and another elm endophyte from Dothideomycetes enhanced host resistance to Dutch elm disease (DED). Here, we hypothesize that the combined effect of these endophytes activate the plant immune and/or antioxidant system, leading to a defense priming and/or increased oxidative protection when exposed to the DED pathogen Ophiostoma novo-ulmi. To test this hypothesis, the short-term defense gene activation and antioxidant response were evaluated in DED-susceptible (MDV1) and DED-resistant (VAD2 and MDV2.3) Ulmus minor genotypes inoculated with O. novo-ulmi, as well as two weeks earlier with a mixture of the above-mentioned endophytes. Endophyte inoculation induced a generalized transient defense activation mediated primarily by salicylic acid (SA). Subsequent pathogen inoculation resulted in a primed defense response of variable intensity among genotypes. Genotypes MDV1 and VAD2 displayed a defense priming driven by SA, jasmonic acid (JA), and ethylene (ET), causing a reduced pathogen spread in MDV1. Meanwhile, the genotype MDV2.3 showed lower defense priming but a stronger and earlier antioxidant response. The defense priming stimulated by elm fungal endophytes broadens our current knowledge of the ecological functions of endophytic fungi in forest trees and opens new prospects for their use in the biocontrol of plant diseases.

Особливості зростання та поширення мохоподібних в умовах міста Запоріжжя

У статті наведені результати досліджень бріофлори двох антропогенних комплексів (культурофітоценозу та селітебного ландшафту) міста Запоріжжя. Визначали місцезнаходження, частоту трапляння, проективне покриття та приуроченість бріофітів до конкретних форофітів на досліджених територіях. Досліджені особливості поширення епіфітних мохоподібних, виявлено їх субстратну приуроченість до найбільш поширених деревних порід. Виділено екологічні групи мохів, їх життєві форми, здійснено оцінку видів за ступенем урбанофільності. Встановлено, що видовий склад досліджених антропогенних комплексів міста представлений 11 видами мохоподібних, з-поміж яких 7 видів є епіфітними, інші види були виявлені на інших субстратах. Серед виявлених мохоподібних 2 види є рідкісними. Найбільша кількість епіфітних бріофітів виявлена на корі Ulmus minor Mill., Populus alba L. та Robinia pseudoacacia L. Середнє видове різноманіття епіфітів характерне для Acer negundo L. та Salix sp. Мохи досліджених територій міста Запоріжжя реалізують життєві стратегії бріоексплерентів піонерних та бріопатієнтів (екотопічних і ценотичних). Встановлений сильний позитивний кореляційний зв’язок між площею проективного покриття бріофітів та висотою їх розташування на форофітах. За результатами розрахунків індексу чистоти повітря, який коливався від 3,4 до 5,0, території селітебного ландшафту та культуроценозу відповідають середньо й слабко забрудненим бріоіндикаційним зонам відповідно. Порівняльний аналіз видового складу бріофітів двох антропогенних комплексів міста Запоріжжя показав високий коефіцієнт спорідненості (0,60) бріофлор досліджених територій. Отже, видовий склад бріофітів цих територій є досить однорідним. Отримані дані свідчать про значну роль епіфітних мохоподібних, які здатні швидко заселяти деревні насадження антропогенних комплексів міста, що є одним із чинників стабілізації урбоекосистеми.

Inventario y caracterización de los olmos (Ulmus spp.) de Oñati (País Vasco) y su utilidad para la detección de poblaciones asociadas de Satyrium w-album.

Los olmos han sufrido un acusado declive en Europa debido a la grafiosis y esta decadencia ha afectado también a las poblaciones de la mariposa Satyrium w-album, cuya oruga se alimenta principalmente de las hojas del olmo. Este trabajo se ha centrado en la evaluación del estado actual de los olmos y la mariposa en el municipio de Oñati (País Vasco). Se ha aprovechado la época de fructificación de los olmos para detectarlos a distancia, localizando un centenar de olmos que superan los 80cm de perímetro normal, pertenecientes a tres especies (Ulmus minor, U. glabra y U. pumila) y repartidos en seis núcleos principales, casi en su totalidad fuera de espacios protegidos. No obstante, se ha comprobado que el retroceso continúa, con la muerte del 17% de los olmos silvestres inventariados en solo dos años. El hábitat principal que ocupan son los bosques de ribera, muy mermados en la actualidad debido a la presión humana. Se detallan los principales factores de riesgo de los olmos, con los problemas fitosanitarios a la cabeza. Se ha propuesto y testado un do de búsqueda de poblaciones de S. w-album, con muestreos en las zonas de mayor densidad de olmos. Su puesta en práctica ha confirmado la conservación de la especie en la única zona con citas previas en el municipio, así como la localización de una nueva población (confirmando su presencia en el 33% de las áreas muestreadas). Estos resultados avalan la validez del método para detectar la especie que podría ser empleado en otras zonas.

Characterizing offspring of Dutch elm disease-resistant trees (Ulmus minor Mill.)

Populations of Ulmus minor in Europe were severely damaged by Dutch elm disease (DED) pandemics. However, elm breeding programmes have permitted selection of resistant elm varieties currently used for reforestation. In restored elm forests, resistant (R) and susceptible (S) trees interbreed, but little is known about resistance in their offspring. In this work, growth, DED resistance and xylem anatomy in the offspring of two resistant U. minor trees (R1 and R2) were studied. To verify whether transmission of traits in offspring is determined by maternal or paternal trees, a complete randomized plot was established with clonal material from controlled crosses (R1 × S and R2 × S) and parent trees (R1, R2 and S). Trees were inoculated with O. novo-ulmi firstly at age 4 years and again at 5 years. Growth, susceptibility to DED and vessel size in offspring were closer to the traits of maternal than of paternal trees. This association disappeared after the second inoculation when symptoms increased. The more resistant trees in R1 × S and R2 × S had wide and narrow earlywood vessels, respectively, suggesting that water-conducting strategies and resistance mechanisms vary in offspring. Tylosis formation was related to resistance only in R2 × S offspring, possibly due to the narrow earlywood vessles of trees. Latewood vessels were normally narrower in the more resistant trees. This study sheds light on anatomical resistance mechanisms of elms against DED: (1) offspring exhibit high variability in responses among individuals, (2) narrow earlywood vessels are not a prerequisite for DED resistance and (3) barrier zones are not fully associated with tree resistance in offspring.

Cellulose Nanofibers from a Dutch Elm Disease-Resistant Ulmus minor Clone

The potential use of elm wood in lignocellulosic industries has been hindered by the Dutch elm disease (DED) pandemics, which have ravaged European and North American elm groves in the last century. However, the selection of DED-resistant cultivars paves the way for their use as feedstock in lignocellulosic biorefineries. Here, the production of cellulose nanofibers from the resistant Ulmus minor clone Ademuz was evaluated for the first time. Both mechanical (PFI refining) and chemical (TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation) pretreatments were assessed prior to microfluidization, observing not only easier fibrillation but also better optical and barrier properties for elm nanopapers compared to eucalyptus ones (used as reference). Furthermore, mechanically pretreated samples showed higher strength for elm nanopapers. Although lower nanofibrillation yields were obtained by mechanical pretreatment, nanofibers showed higher thermal, mechanical and barrier properties, compared to TEMPO-oxidized nanofibers. Furthermore, lignin-containing elm nanofibers presented the most promising characteristics, with slightly lower transparencies.

Endophyte inoculation enhances Ulmus minor resistance to Dutch elm disease

Certain fungal endophytes are known to improve plant resistance to biotic stresses in forest trees. In this study, three stem fungal endophytes belonging to classes Cystobasidiomycetes, Eurotiomycetes and Dothideomycetes were selected from 210 isolates for their potential as enhancers of Ulmus minor resistance to Ophiostoma novo-ulmi. We evaluated phenotypic traits of these endophytes that could be beneficial for inhibiting O. novo-ulmi in the host plant. Under in vitro conditions, the Dothideomycetous isolate YCB36 strongly inhibited O. novo-ulmi growth, released antipathogenic VOCs, chitinases and siderophores, and overlapped with the pathogen in nutrient utilization patterns. These functional traits could explain the 40% reduction in leaf wilting due to O. novo-ulmi in elm trees pre-inoculated with this endophyte. Ulmus minor trees inoculated with this endophyte showed increased leaf stomatal conductance and higher concentrations of flavonoids and total phenolic compounds in xylem tissues, suggesting induction of defence metabolism.