Spotlight on the Roles of Whitefly Effectors in Insect–Plant Interactions

Abstract

The Bemisia tabaci species complex (whitefly) causes enormous agricultural losses. These phloem-feeding insects induce feeding damage and transmit a wide range of dangerous plant viruses. Whiteflies colonize a broad range of plant species that appear to be poorly defended against these insects. Substantial research has begun to unravel how phloem feeders modulate plant processes, such as defense pathways, and the central roles of effector proteins, which are deposited into the plant along with the saliva during feeding. Here, we review the current literature on whitefly effectors in light of what is known about the effectors of phloem-feeding insects in general. Further analysis of these effectors may improve our understanding of how these insects establish compatible interactions with plants, whereas the subsequent identification of plant defense processes could lead to improved crop resistance to insects. We focus on the core concepts that define the effectors of phloem-feeding insects, such as the criteria used to identify candidate effectors in sequence-mining pipelines and screens used to analyze the potential roles of these effectors and their targets in planta. We discuss aspects of whitefly effector research that require further exploration, including where effectors localize when injected into plant tissues, whether the effectors target plant processes beyond defense pathways, and the properties of effectors in other insect excretions such as honeydew. Finally, we provide an overview of open issues and how they might be addressed.

Interactions between insect vectors and plant pathogens span the parasitism-mutualism continuum

“…Previously, some of the large variation in vector fitness effects has been attributed to differences in methods (60). For example, plant hosts inoculated mechanically vs vector inoculated will not induce processes such as herbivore effector triggered immunity or other changes to plant chemical composition (61)(62)(63).However, inoculation method did not explain much of the variation in vector fitness, suggesting these methods are more comparable than previously assumed. Notably, negative fitness outcomes were slightly more prevalent if the vector was the only party infected in the experiment.…”

Interactions between insect vectors and plant pathogens span the parasitism–mutualism continuum

“…Methodological differences frequently drive variation in study outcomes. For example, plant hosts inoculated mechanically versus vector inoculated will not induce processes such as herbivore effector-triggered immunity or other changes to plant chemical composition [61][62][63]. However, inoculation method explained little of the variation in vector fitness, suggesting methods may be relatively comparable.…”

Differential levels of soybean resistance to the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) under controlled and uncontrolled environments are associated with plant age, damage intensity, and trichome density

“…The whitefly Bemisia tabaci genn (Hemiptera: Aleyrodidae) is a phloem sap-feeding polyphagous insect pest that has become the most destructive pest of various agricultural commodities worldwide (Satar et al 2018;Manivannan et al 2021;Naalden et al 2021;Zhang et al 2021), including soybean (Arnemann et al 2019;Ayala et al 2020;Barros et al 2021). Previous investigations have reported that there are currently more than 1550 described species of whiteflies recorded worldwide (Martin et al 2007), with the preferred host species for B. tabaci being plants from Compositae, Cruciferae, Cucurbitaceae, Solanaceae, and Leguminosae (Li et al 2011).…”