Horizontal transmission of the insect symbiont <i>Rickettsia</i> is plant-mediated

TLDR

Rickettsia, known as vertebrate pathogens vectored by blood‑feeding arthropods, are also found in phytophagous insects, suggesting a plant‑mediated transmission route that could influence host ecology and evolution. The study aims to identify a mechanism for horizontal transmission of Rickettsia among evolutionarily distant arthropod hosts. Live insect experiments, molecular analyses, and microscopy revealed that Rickettsia can move from whiteflies into plant phloem and be subsequently acquired by other whiteflies. Rickettsia was transferred to cotton, basil, and black nightshade leaves, remained confined to phloem cells, and was readily acquired by Rickettsia‑free whiteflies sharing the leaf, indicating that plants serve as reservoirs for horizontal transmission and may explain the presence of similar symbionts in unrelated phytophagous insects.

Abstract

Bacteria in the genus Rickettsia , best known as vertebrate pathogens vectored by blood-feeding arthropods, can also be found in phytophagous insects. The presence of closely related bacterial symbionts in evolutionarily distant arthropod hosts presupposes a means of horizontal transmission, but no mechanism for this transmission has been described. Using a combination of experiments with live insects, molecular analyses and microscopy, we found that Rickettsia were transferred from an insect host (the whitefly Bemisia tabaci ) to a plant, moved inside the phloem, and could be acquired by other whiteflies. In one experiment, Rickettsia was transferred from the whitefly host to leaves of cotton, basil and black nightshade, where the bacteria were restricted to the phloem cells of the plant. In another experiment, Rickettsia -free adult whiteflies, physically segregated but sharing a cotton leaf with Rickettsia -plus individuals, acquired the Rickettsia at a high rate. Plants can serve as a reservoir for horizontal transmission of Rickettsia , a mechanism which may explain the occurrence of phylogenetically similar symbionts among unrelated phytophagous insect species. This plant-mediated transmission route may also exist in other insect–symbiont systems and, since symbionts may play a critical role in the ecology and evolution of their hosts, serve as an immediate and powerful tool for accelerated evolution.