Flower malformation represented by phyllody is a common symptom of phytoplasma infection induced by a novel family of phytoplasma effectors called phyllogens. Despite the accumulation of functional and structural phyllogen information, the molecular mechanisms of phyllody have not yet been integrated with their evolutionary aspects due to the limited data on their homologs across diverse phytoplasma lineages. Here, we developed a novel universal PCR‐based approach to identify 25 phytoplasma phyllogens related to nine “Candidatus Phytoplasma” species, including four species whose phyllogens have not yet been identified. Phylogenetic analyses showed that the phyllogen family consists of four groups (phyl‐A, ‐B, ‐C, and ‐D) and that the evolutionary relationships of phyllogens were significantly distinct from those of phytoplasmas, suggesting that phyllogens were transferred horizontally among phytoplasma strains and species. Although phyllogens belonging to the phyl‐A, ‐C, and ‐D groups induced phyllody, the phyl‐B group lacked the ability to induce phyllody. Comparative functional analyses of phyllogens revealed that a single amino acid polymorphism in phyl‐B group phyllogens prevented interactions between phyllogens and A‐ and E‐class MADS domain transcription factors (MTFs), resulting in the inability to degrade several MTFs and induce phyllody. Our finding of natural variation in the function of phytoplasma effectors provides new insights into molecular mechanisms underlying the aetiology of phytoplasma diseases.

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Phyllogen, a bacterial virulence factor, induced phyllody in various eudicot species, and had broad-spectrum degradation activity on MADS domain transcription factors of plants, suggesting phyllogen universally functions in plants.

Bogia coconut syndrome (BCS) is one of the lethal yellowing (LY)-type diseases associated with phytoplasma presence that are seriously threatening coconut cultivation worldwide. It has recently emerged, and is rapidly spreading in northern parts of the island of New Guinea. BCS-associated phytoplasmas collected in different regions were compared in terms of 16S rRNA gene sequences, revealing high identity among them represented by strain BCS-Bo. Comparative analysis of the 16S rRNA gene sequences revealed that BCS-Bo shared less than a 97.5 % similarity with other species of 'Candidatus Phytoplasma', with a maximum value of 96.08 % (with strain LY; GenBank accession no. U18747). This result indicates the necessity and propriety of a novel taxon for BCS phytoplasmas according to the recommendations of the IRPCM. Phylogenetic analysis was also conducted on 16S rRNA gene sequences, resulting in a monophyletic cluster composed of BCS-Bo and other LY-associated phytoplasmas. Other phytoplasmas on the island of New Guinea associated with banana wilt and arecanut yellow leaf diseases showed high similarities to BCS-Bo and were closely related to BCS phytoplasmas. Based on the uniqueness of their 16S rRNA gene sequences, a novel taxon 'Ca.Phytoplasma noviguineense' is proposed for these phytoplasmas found on the island of New Guinea, with strain BCS-Bo (GenBank accession no. LC228755) as the reference strain. The novel taxon is described in detail, including information on the symptoms of associated diseases and additional genetic features of the secY gene and rp operon.

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. Many plant pathogens of agricultural importance are persistently transmitted by insect vectors 1,2. The circulation of these pathogens within insect vectors involves several steps: (i) entry into and multiplication in gut epithelial cells of the alimentary canal, (ii) entry into the hemocoel and circulation in hemolymph, and (iii) final entry into and multiplication in salivary glands, which results in successful pathogen transmission to new plants via insect saliva 2-4. Previous studies of plant viruses and plant pathogenic bacteria have shown that the alimentary canal and salivary glands are the major organs that determine vector competence 3-5. Thus, the timing and location of insect-borne plant pathogen infection and passage through the target organs is fundamental to the understanding of underlying infection mechanisms. The infection site 6,7 and temporal localization 8 of spiroplasmas (Spiroplasma citri and S. kunkelii) have been revealed by transmission electron microscopy (TEM) studies of infected alimentary canal and salivary glands of leafhoppers (Circulifer tenellus and Dalbulus maidis). In addition, the localizations of spiroplasma (S. kunkelii) 9 and liberibacter ('Candidatus Liberibacter asiaticus') 10 in their vector organs have also been visualized by fluorescence microscopic studies. However, spatial and temporal distribution patterns of these bacterial pathogens at the organ level remain elusive. Phytoplasmas are cell wall-less plant pathogenic bacteria that, together with spiroplasmas, belong to the class Mollicutes. They infect more than 1,000 plant species and cause severe losses in the yields of many important crops world...