OOS 12-7 - Leafminer insects trigger the host plant physiology through an unexpected association with endosymbiotic bacteria

Tuesday, August 9, 2011: 9:50 AM
15, Austin Convention Center
David Giron1, Wilfried Kaiser1, Mélanie Body1, Elisabeth Huguet1, Arnaud Lanoue2, Gaëlle Glevarec2 and Jérôme Casas1, (1)Institut de Recherche sur la Biologie de l'Insecte, Centre National de la Recherche Scientifique - University of Tours, Tours, France, (2)Biomolécules et Biotechnologies Végétales, University of Tours, Tours, France

Phytophagous insects can be divided in two large groups according to their feeding habit: ectophages feeding externally on plant tissues and endophages living concealed within plant tissues and feeding internally. In spite of a reasonable understanding of the history and origins of the endophagous feeding habit, its evolution and adaptive significance remains unclear. Three major hypotheses have been proposed to explain the endophagous-feeding life history mode: The nutrition hypothesis, the microenvironment hypothesis and the enemy hypothesis. Among these hypotheses, feeding selectively on the most nutritional tissues is undoubtedly considered as a major advantage and most probably played a major role in the emergence, evolution and/or radiation of the endophagous feeding mode. This behavior can also be reinforced by manipulating the plant physiology and gall-inducer arthropods are usually distinguished from other insect-generated shelters by the fact that they involve active plant physiological alterations such as the differentiation of additional tissues to feed on, the upregulation of protein and/or sugar synthesis in situ, and/or the modification of source-sink relationships leading to nutrient translocation towards the insect’s feeding site. However, plant manipulation appears not to be restricted to gall-inducers only, as suggested by the autumnal formation of ‘green-islands’ around mining caterpillars in yellow leaves.

We aim to understand proximal and ultimate mechanisms at the basis of a plant-herbivore adaptive life-style. This necessitates studying the intimate molecular, biochemical and physiological mechanisms used by leaf-miner insects to manipulate their host-plant environment but also their fitness consequences for the insect.


Our results on the Malus domestica/Phyllonorycter blancardella plant-leaf mining system show: (i) The ability of this leaf-miner caterpillar to manipulate its host plant in order to generate a microenvironment with all the nutrient supply needed for its survival. (ii) A decrease in plant defence compounds within the mined area. (iii) A large accumulation of cytokinins in the mined tissues which is responsible for the preservation of functional nutrient-rich green tissues at a time when leaves are otherwise turning yellow. (iv) The primary role played by endosymbiotic bacteria (Wolbachia) in the synthesis of these cytokinins and in the induction of nutrient-rich tissues. All together, these results clearly show the ability of leaf-miner insects to manipulate their host plant physiology and to create an “optimal” nutritional micro-environment through cytokinin production by their endosymbiotic partners. Wolbachia is suspected to play an essential role which, if this is the case, will be the first evidence of a Wolbachia-mediated effect on plant physiology.

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