Abstract
Bacterial symbionts associated with insects are often involved in host development and ecological adaptation. Serratia symbiotica, a common facultative endosymbiont harbored in pea aphids, improves host fitness and heat tolerance, but studies concerning the nutritional metabolism and impact on the aphid host associated with carrying Serratia are limited. In the current study, we showed that Serratia-infected aphids had a shorter nymphal developmental time and higher body weight than Serratia-free aphids when fed on detached leaves. Genes connecting to fatty acid biosynthesis and elongation were up-regulated in Serratia-infected aphids. Specifically, elevated expression of fatty acid synthase 1 (FASN1) and diacylglycerol-o-acyltransferase 2 (DGAT2) could result in accumulation of myristic acid, palmitic acid, linoleic acid, and arachidic acid in fat bodies. Impairing fatty acid synthesis in Serratia-infected pea aphids either by a pharmacological inhibitor or through silencing FASN1 and DGAT2 expression prolonged the nymphal growth period and decreased the aphid body weight. Conversely, supplementation of myristic acid (C14:0) to these aphids restored their normal development and weight gain. Our results indicated that Serratia promoted development and growth of its aphid host through enhancing fatty acid biosynthesis. Our discovery has shed more light on nutritional effects underlying the symbiosis between aphids and facultative endosymbionts.
Highlights
Insects are a highly successful group of animals, and some of them are able to utilize a wide range of nutrient-unbalanced food resources from the plant phloem sap to animal blood [1,2]
To determine the effect of Serratia infection on the performance of pea aphids, developmental time, body weight, and fecundity were compared between Serratia-free and Serratia-infected aphids when fed on detached broad bean leaves
The facultative endosymbionts are often beneficial to aphid hosts when challenged by environmental stresses, but unfavorably affect host fitness when the stress is relieved [15]
Summary
Insects are a highly successful group of animals, and some of them are able to utilize a wide range of nutrient-unbalanced food resources from the plant phloem sap to animal blood [1,2]. Heritable microbial symbionts are reported to shape insect adaption to diverse feeding habits [3,4]. The pea aphid Acyrthosiphon pisum usually hosts one obligate symbiont. Buchnera and several facultative symbionts [5,6]. Buchnera offers essential amino acids to aphids, crucial for their survival on nutrition-unbalanced phloem sap [7]. The facultative symbionts are usually unnecessary for host survival and reproduction. Instead, they improve the fitness and adaption of the aphid to environments [8]
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