Newly Distinguished Cell Punctures Associated with Transmission of the Semipersistent Phloem-Limited Beet Yellows Virus.

Abstract

Here we report on plant penetration activities (probing) by the aphid Myzus persicae (Sulzer, 1776) in association with the transmission, acquisition, and inoculation of the semipersistent Beet yellows virus (BYV; Closterovirus) in sugar beet. During electrical penetration graph (EPG) recording of stylet pathways, standard intracellular stylet punctures occur which are called potential drop (pd) waveforms. In addition to the standard pd, there also appeared to be a unique type of intracellular stylet puncture that always preceded the phloem salivation phase (waveform E1). This type of pd, the phloem-pd, showed properties distinct from those of the standard pds and has never been described before. We manually ended EPG recordings during the acquisition and inoculation tests by removing aphids from the source or test plant after specific waveforms were recorded. Inoculation of BYV occurred at the highest rate when probing was interrupted just after a single or various phloem-pds. In contrast, BYV acquisition showed an intimate association with sustained phloem sap ingestion from phloem sieve elements (SEs) (E2 waveform). Our work shows for the first time that the inoculation of a phloem-limited virus occurs during specific intracellular stylet punctures and before phloem salivation (waveform E1). Further studies are needed to establish in what cells this novel phloem-pd occurs: phloem parenchyma, companion, or SE cells. The role of the different stylet activities in the acquisition and inoculation of BYV by M. persicae is discussed.IMPORTANCE We discovered the specific feeding activities of Myzus persicae (Sulzer, 1776) associated with the transmission of Beet yellows virus (BYV; Closterovirus). Our work strongly suggests that aphids can insert their stylets into the membranes of phloem cells-visualized as a unique type of waveform that is associated with the inoculation of BYV. This intracellular puncture (3 to 5 s) occurs just before the phloem salivation phase and can be distinguished from other nonvascular stylet cell punctures. This is the first time that the transmission of a phloem-limited semipersistent virus has been shown to be associated with a unique type of intracellular puncture. Our work offers novel information and strongly contributes to the existing literature on the transmission of plant viruses. Here we describe a new kind of aphid behavioral pattern that could be key in further works, such as studying the transmission of other phloem-limited viruses (e.g., luteoviruses).