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.

Insect Bacterial Symbiont-Mediated Vitellogenin Uptake into Oocytes To Support Egg Development

ABSTRACT Many insect species, such as aphids, leafhoppers, planthoppers, and whiteflies harbor obligate bacterial symbionts that can be transovarially transmitted to offspring through the oocytes of female insects. Whether obligate bacterial symbionts can carry important molecules/resources to the embryos to support egg development is still unknown. Here, we show that the vitellogenin (Vg) precursor of rice leafhopper Nephotettix cincticeps is biosynthesized by the fat body, secreted into the hemolymph and subsequently cleaved into the 35- and 178-kDa subunits, whereas only the 178-kDa subunit is taken up by the leading end of oocytes in a receptor-dependent manner or moves into the posterior pole of the terminal oocyte in association with obligate bacterial symbiont “Candidatus Nasuia deltocephalinicola” (hereafter Nasuia) in a receptor-independent manner. Furthermore, the 178-kDa Vg subunit can directly interact with a surface channel molecule (porin) on the envelope of Nasuia, allowing Vg to enter bacterial cytoplasm. Thus, Vg can hitchhike the ancient oocyte entry path of Nasuia, the common obligate symbiont of leafhoppers. Knocking down a Nasuia growth-related protein expression or treatment with porin antibody strongly prevents the ability of Nasuia to carry Vgs into oocytes and impair insect egg development. Nasuia-carried Vgs provide at least 20% of the total Vgs in the developing eggs. We anticipate that the bacterial symbiont-mediated Vg uptake into oocytes to support efficient egg development may be a common pattern shared by many insects. IMPORTANCE Many insects harbor obligate bacterial symbionts that can be vertically transmitted to offspring by female insects through eggs. Here, we report that leafhopper vitellogenin (Vg) recognizes and binds a surface channel molecule (porin) on the envelope of obligate bacterial symbiont Nasuia, which potentially induces the opening of porin channels for Vg to access the cytoplasm of Nasuia. Thus, Vg can exploit bacterial symbionts as the independent carriers into the oocytes. Such Nasuia-carried Vg contents support efficient insect egg development. Thus, our findings indicate that insects have evolved strategies to exploit the symbionts for carrying additional Vgs to guarantee optimal insect reproduction.

Pengaruh iradiasi sinar gamma terhadap fertilitas Sternochetus frigidus (Fabricius) (Coleoptera: Curculionidae) pada mangga kuini

<p>One of the recognized and safe quarantine treatments for consumers is the use of gamma-ray irradiation [⁶⁰Co] at a recommended dose requested by the destination country or international agency. The purpose of this study was to test the effectiveness of a generic dose of gamma ray irradiation for sterilizing mango pulp weevil <em>Sternochetus frigidus</em> (Fabricius) on mangoes cv kuini (<em>Mangifera odorata</em>). A total of 300 kg pulp-weevil-infested mango fruits was collected from West Sumatra and Lampung. First experiment was conducted on April to irradiate fruits collected from West Sumatera and second experiment was on May to irradiate fruits collected from Lampung. In each treatment, a box containing 6-8 <em>M. odorata </em>fruits was irradiated with gamma-ray at doses of 50, 100, 150, 200, 300, 400 Gy with three replications. The treatment of gamma-ray irradiation could reduce feeding activity, normal life of insect, egg production and increase mortality of adults. The results of the first and second experiments showed that gamma ray irradiation was able to influence the development of pupae and adults. There were differences in the normal development of adults in the two experiments. The number of normal development of adults on first experiment was higher than on the second experiment. The irradiated pupae at dose of 100 Gy successfully develop to be adults but the adults are unable to produce eggs. Adults irradiated at 150 Gy are still able to lay eggs with the average of 6 eggs (first experiment) and 2,3 larvae (experiment II), 150 Gy average 6 eggs and do not hatch. Doses at 200 Gy no eggs were produced.</p>