Phytoplasma infection influences gene expression in American cranberry

Authors: PRADIT, NAKORN - Rutgers University; RODRIGUEZ-SAONA, CESAR - Rutgers University; KAWASH, JOSEPH - Orise Fellow; Polashock, James

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 5/24/2019
Citation: Pradit, N., Rodriguez-Saona, C., Kawash, J., Polashock, J.J. 2019. Phytoplasma infection influences gene expression in American cranberry. Frontiers in Ecology and Evolution. 7:178. https://doi.org/10.3389/fevo.2019.00178.
DOI: https://doi.org/10.3389/fevo.2019.00178

Interpretive Summary: Phytoplasmas are a type of plant pathogenic bacterium. Phytoplasma infection in cranberries causes a disease called false blossom, which stimulates excessive branching of the vines and the abnormality and malfunction of flowers, thus reducing yield. The phytoplasma is transmitted to cranberry plants by sucking insects called leafhoppers. To determine how cranberry plants react to infection by phytoplasmas, we studied the changes in cranberry plant gene expression when infected with the phytoplasma relative to healthy plants. These analyses showed that phytoplasma infection induces 132 genes, and suppresses 225 genes, in cranberries. The induced genes are involved in nutrient metabolism and the suppressed genes are generally involved in plant defense. This study supports the “host manipulation hypothesis,” where phytoplasma infection in cranberries alters the expression of plant genes that likely enhance attractiveness of host plants for insect vectors and thus promote disease transmission. These data can be used to develop genetic markers in cranberry to facilitate breeding for resistance to the disease. The information reported herein will be useful to plant pathologists and breeders studying phytoplasma diseases in cranberry and other crops, as well as entomologists studying the leafhopper vector of the disease.

Technical Abstract: Phytoplasma infection in cranberries causes false blossom disease, which stimulates branching of the vines (witches’ broom) and the abnormality and malfunction of floral structures. The phytoplasma is vectored by leafhoppers. In this study, we compared the transcriptome profiles between phytoplasma-infected and healthy cranberry plants using RNA-Seq. The de novo transcriptome assembly consisted of 131,404 unigenes. From these unigenes, 63.59% were annotated in at least one of the databases examined. As compared with healthy plants, gene expression analyses showed that phytoplasma infection induces 132 unigenes, and suppresses 225 unigenes, in cranberries. Analyses of differentially expressed genes between healthy and infected plants indicates that the majority of these genes are associated with primary and secondary metabolism pathways. Phytoplasma infection upregulated genes associated with nutrient metabolism (i.e., galactose, amino acid, and fatty acid metabolism), while downregulating genes associated with defensive pathways (i.e., phenylpropanoid and terpene syntheses) and fatty acid metabolism. These data indicate that phytoplasma infection enhances expression of genes linked to nutrient biosynthesis while reducing those associated with defenses in cranberries. This study supports the “host manipulation hypothesis,” where phytoplasma infection in cranberries alters the expression of genes to likely enhance host quality for insect vectors and thus promote its transmission.