Dramatic Transcriptional Changes in an Intracellular Parasite Enable Host Switching between Plant and Insect

Phytoplasmas are bacterial plant pathogens that have devastating effects on the yields of crops and plants worldwide. They are intracellular parasites of both plants and insects, and are spread among plants by insects. How phytoplasmas can adapt to two diverse environments is of considerable interest; however, the mechanisms enabling the “host switching” between plant and insect hosts are poorly understood. Here, we report that phytoplasmas dramatically alter their gene expression in response to “host switching” between plant and insect. We performed a detailed characterization of the dramatic change that occurs in the gene expression profile of Candidatus Phytoplasma asteris OY-M strain (approximately 33% of the genes change) upon host switching between plant and insect. The phytoplasma may use transporters, secreted proteins, and metabolic enzymes in a host-specific manner. As phytoplasmas reside within the host cell, the proteins secreted from phytoplasmas are thought to play crucial roles in the interplay between phytoplasmas and host cells. Our microarray analysis revealed that the expression of the gene encoding the secreted protein PAM486 was highly upregulated in the plant host, which is also observed by immunohistochemical analysis, suggesting that this protein functions mainly when the phytoplasma grows in the plant host. Additionally, phytoplasma growth in planta was partially suppressed by an inhibitor of the MscL osmotic channel that is highly expressed in the plant host, suggesting that the osmotic channel might play an important role in survival in the plant host. These results also suggest that the elucidation of “host switching” mechanism may contribute to the development of novel pest controls

General and specific combining ability in tropical winter cauliflower

ABSTRACT Few Brazilian cauliflower cultivars have shown to be adapted to tropical winter conditions. In addition, studies to obtain hybrids adapted to our winter conditions, from breeding lines originating from tropical regions, are scarce. The objective of this work was to estimate the combining ability of cauliflower breeding lines. The experiment comprised 38 genotypes, 36 hybrids from a partial diallel cross obtained by crosses between two groups of cauliflower lines: Group I (3 parents) and Group II (12 parents) and 2 commercial controls. We evaluated plant cycle, resistance to diseases, average curd mass, curd color, hollow stalk incidence, and overall evaluation. Additive genetic effects were more important than non-additive effects in the expression of these traits. No single parental line showed simultaneously the most favorable GCA values for all traits. The most promising hybrids were the combinations BR1 x TE6, BR1 x TE8, BR1 x TE12, BR2 x TE11, BR3 x TE6 and BR3 x TE7. The results of the choice of hybrids made by the method of independent culling levels reflect what it could be predicted by estimating GCA for cycle and average mass of the curd, reaffirming the importance of additive effects in the expression of these traits.</jats:p

Interaction between the membrane protein of a pathogen and insect microfilament complex determines insect-vector specificity

Many insect-transmissible pathogens are transmitted by specific insect species and not by others, even if they are closely related. The molecular mechanisms underlying such strict pathogen–insect specificity are poorly understood. Candidatus Phytoplasma asteris, OY strain, line W (OY), is a phytopathogenic bacterium transmitted from plant to plant by sap-feeding insect vectors (leafhoppers). Our study focused on an abundant cell-surface membrane protein of the phytoplasma named antigenic membrane protein (Amp), which is not homologous with any reported functional protein. Immunofluorescence microscopy of the phytoplasma-infected insect showed that OY phytoplasma was localized to the microfilaments of the visceral smooth muscle surrounding the insect’s intestinal tract. The affinity column assay showed that Amp forms a complex with three insect proteins: actin, myosin heavy chain, and myosin light chain. Amp–microfilament complexes were detected in all OY-transmitting leafhopper species, but not in the non-OY-transmitting leafhoppers, suggesting that the formation of the Amp–microfilament complex is correlated with the phytoplasma-transmitting capability of leafhoppers. Although several studies have reported interactions between pathogens and mammalian microfilaments, this is an example of host-specific interactions between a bacterial surface protein and a host microfilament in insect cells. Our data also suggest that the utilization of a host microfilament may be a universal system for pathogenic bacteria infecting mammals or insects