Chemical Communication in Plant-Aphid Interactions

Mechanisms that maintain and separate pea aphid host races

Dr. Grit Kunert

The pea aphid, Acyrthosiphon pisum (Harris), is actually a complex of distinct races that each is specialized on a native host plant of the legume family [Peccoud, J., Ollivier, A. et al. (2009) and Peccoud, J. and J. C. Simon (2010)]. Some aphid races are able to survive on several plant species, while others only survive on just one or a few plant species. However, all pea aphid host races can develop on the universal host plant Vicia faba. This ecological specialization can be considered as one of the first steps towards sympatric speciation since the host fidelity of races leads to assortative mating which reduces gene flow between host-races. In our group we enter into the questions why some aphid races are able to feed on a certain legume plant whilst the same plant is unsuitable for another aphid race. What makes certain legume plants resistant to some aphid races? And what might aphid races force to feed on a certain legume plant?

Cooperation partners: Dr. Jean-Christophe Simon, INRA, Université Rennes 1, France; Dr. Akiko Sugio, INRA, Université Rennes 1, France; Dr. Alexandra Furch, Friedrich Schiller University, Institute of General Botany and Plant Physiology, Jena; Dr. Sylvia Anton, INRA, Université d'Angers, Neuroéthologie-RCIM, France; Dr. Torsten Will: Julius Kühn-Institut (JKI), Quedlinburg, Germany



Legume chemistry and the specificity of pea aphid races

Carlos Fernando Sánchez Arcos

Each pea aphid host races is specialized on a native host plant of the legume family. The role of the host plant chemistry for this adaptation has not been studied in depth, so the main objective of this project will be the isolation, purification, identification, and evaluation of chemical compounds from Pisum sativum, Vicia faba, Medicago sativa and Trifolium pratense involved in aphid – host plant specialization.

Interaction between legume chemistry and facultative symbiosis

Dr. Elizabeth Pringle, Dr. Grit Kunert

Our project investigates feedbacks between plant chemistry and the facultative mutualisms between pea aphids and two of their "secondary" bacterial endosymbionts (Regiella insecticola and Rickettsia sp.). Previous research has suggested that aphid genotype x symbiont genotype interactions strongly affect pea-aphid performance on the different pea-aphid host plants. We are studying how plants respond hormonally and metabolically to feeding by different pea-aphid host races experimentally infected with the same genotype of endosymbiotic bacteria, as well as how these responses ultimately affect pea-aphid performance and host-plant choice.



Phloem associated defense mechanisms in relation to host races in the pea aphid complex

Maria Paulmann, Dr. Alexandra Furch, Dr. Grit Kunert

Plants have evolved striking defenses to protect themselves from aphid attack. When pea aphids puncture sieve elements and other cells upon feeding, Ca2+-influx will lead to an accumulation of reactive oxygen species (ROS), the formation of callose, the dispersion of forisomes and further defense reactions. Forisomes for instance are large protein bodies situated in the sieve elements of legumes that reversibly block the phloem-mass flow by dispersing and which can prevent aphid feeding. We will investigate these early plant defense mechanisms and see whether they differ between plants infested with native and non-native aphid host races and therefore, might play a role in aphid host race maintenance. We will study the oxidative state and the configuration of forisomes in different legume species infested by several pea aphid host races.

Light microscopy view of phloem in Vicia faba. A) shows the condensed forisome (F) in a phloem sieve element (SE) before burning the leaf tip. B) After 0:25 min the forisome disperses. C) Partial recondensation of the forisome. D) The forisome recovered and is fully condensed. PC – parenchyma cell; SP – sieve plate.



Aphid stylectomy

Dr. Torsten Knauer

To learn more about the mechanisms of chemical resistance of legume plant species against aphids we have to search for chemical compounds directly at the feeding site of the aphids. In the case of piercing-sucking aphids this is the phloem consisting of sieve elements and companion cells. Next to phloem exudation, we use the only existing technique which allows collecting pure phloem sap – the aphid stylectomy. With this technique the aphid itself is used as a tool to reach the phloem cells. Stylets of feeding aphids are cut and leaking sieve tube sap is collected and can be further analyzed. With this technique we will investigate changes in phloem sap composition of legume plants due to infestation with different pea aphid biotypes.

The role of quinolizidine alkaloids (QA) from Genista (Fabaceae) in aphid-plant interactions

Felix Feistel

QA’s represent about 2% of the approximately 7000 known alkaloids from plants, and they are characteristic metabolites of the genus Genista belonging to the legume family (Fabaceae). QA’s are able to stimulate and even paralyze the central nervous system with sometimes fatal consequences for the organism. Also non-native pea aphid races die quickly when trying to feed on Genista plants, or diet containing Genista extracts. The pea aphid host race native to Genista plants, however, is able to perform on Genista plant species as well as on diet containing Genista extract.

In this project we will investigate the role of QA compounds and their relevance as defense substances for both the plant and the insect.


Former group members:

Dr. Eduardo Hatano: PhD thesis (2009) Chemical communication in an aphid-natural enemy system: new mechanisms of aphid alarm signalling and wing induction. Supervised by Prof. Wolfgang Weisser , now PostDoc at North Carolina State University, Department of Entomology, Raleigh NC, USA

Carolina Reinhold: Diploma thesis (2011): Der Einfluss von (E)-β-Farnesen auf das Wirtswahlverhalten von Myzus persicae

Susanne Seyfarth: Diploma thesis (2013): Der Aminosäure- und Zuckergehalt von Pflanzen in Abhängigkeit vom Blattlausbefall

Daniel Rosenberger: Technical assistant (2008-2012)

Dr. Ilka Vosteen: PhD thesis (2015): Searching behavior of aphid natural enemies and its implication for host-race maintenance in the pea aphid complex; now PostDoc at Wageningen University and Research, Laboratory of Entomology, Netherlands

Dr. Alexander Schwarzkopf: PhD thesis: Electrophysiological localization of plant factors affecting pea aphid (Acyrthosiphon pisum) compatibility to host and non-host plants; now Director of Coordination office UniKoN, FSU Jena, Germany