Abstract
Phytoplasmas are transmitted by insect vectors in a persistent propagative manner; however, detailed movements and multiplication patterns of phytoplasmas within vectors remain elusive. In this study, spatiotemporal dynamics of onion yellows (OY) phytoplasma in its vector Macrosteles striifrons were investigated by immunohistochemistry-based 3D imaging, whole-mount fluorescence staining, and real-time quantitative PCR. The results indicated that OY phytoplasmas entered the anterior midgut epithelium by seven days after acquisition start (daas), then moved to visceral muscles surrounding the midgut and to the hemocoel at 14–21 daas; finally, OY phytoplasmas entered into type III cells of salivary glands at 21–28 daas. The anterior midgut of the alimentary canal and type III cells of salivary glands were identified as the major sites of OY phytoplasma infection. Fluorescence staining further revealed that OY phytoplasmas spread along the actin-based muscle fibers of visceral muscles and accumulated on the surfaces of salivary gland cells. This accumulation would be important for phytoplasma invasion into salivary glands, and thus for successful insect transmission. This study demonstrates the spatiotemporal dynamics of phytoplasmas in insect vectors. The findings from this study will aid in understanding of the underlying mechanism of insect-borne plant pathogen transmission.
Highlights
Phytoplasmas are transmitted by insect vectors in a persistent propagative manner; detailed movements and multiplication patterns of phytoplasmas within vectors remain elusive
Spatiotemporal distribution of onion yellows (OY) phytoplasmas in entire insect vector based on 3D imaging technology
Our previous studies have successfully detected OY phytoplasmas in insect vectors by immunohistochemical staining, using an antibody raised against an immunodominant membrane protein (Amp) of OY phytoplasma[25,26,27]
Summary
Phytoplasmas are transmitted by insect vectors in a persistent propagative manner; detailed movements and multiplication patterns of phytoplasmas within vectors remain elusive. ELISA- and PCR-based analyses can detect and quantify specific phytoplasmas at the whole-body, organ, or tissue levels[17,18,20,21,22,23,24]; they cannot determine whether phytoplasmas are located inside or outside the organs Because these methods have been used independently in most studies, a detailed understanding is lacking with respect to the movements and multiplication patterns of phytoplasmas in insect vectors, the timing and locations of phytoplasma passage through various insect organs, such as the alimentary canal and salivary glands; most importantly, there remains a lack of clarity regarding the duration and abundance of phytoplasmas accumulated in each organ. Our findings from this study provide information regarding the underlying mechanism of insect-borne plant pathogen transmission
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