Phytoplasma Infection Influences Gene Expression in American Cranberry

Abstract

Cranberry false blossom disease (CFBD) is caused by a leafhopper-vectored phytoplasma infection. CFBD results in distinctive branching of the upright shoots (witches' broom) and the formation of deformed flowers that fail to produce fruit. This disease is reemerging and poses a serious threat to the cranberry industry. To determine the impact of the disease on host gene expression, we compared transcriptome profiles between plants with CFBD and uninfected cranberry plants. We found that phytoplasma infection induced expression of 132 genes, and suppressed 225 genes, compared to uninfected cranberry plants. Differentially expressed genes between uninfected and infected plants were largely associated with primary and secondary metabolic, defensive, and developmental pathways. Phytoplasma infection increased the expression of genes associated with nutrient metabolism, while suppressing genes associated with defensive pathways. This expression profile change supports the "host manipulation hypothesis," whereby CFBD enhances host quality for insect vectors, thus promoting phytoplasma transmission.

Application of Plant Defense Elicitors Fails to Enhance Herbivore Resistance or Mitigate Phytoplasma Infection in Cranberries

“…Previous studies examining the effects of phytoplasma infection on phytohormones have produced mixed results ( Dermastia, 2019 ), with some showing activation of the SA pathway ( Ahmad et al, 2013 ; Prezelj et al, 2016 ), while others have shown activation of the JA pathway ( Musetti et al, 2013 ; Luge et al, 2014 ; Paolacci et al, 2017 ). Contrary to this study, however, previous studies in cranberries found no effect of phytoplasma infection on SA concentrations ( Pradit et al, 2020 ) or on the expression of SA-related genes ( Pradit et al, 2019b ). Although the mechanisms underlying the variable effects of infection observed across study systems remain unclear, it is known that phytohormone levels can change based on plant age and growing conditions ( Paolacci et al, 2017 ).…”

“…The target gene (“UnkPhyto”) was selected based on previous transcriptome data and RT-qPCR data showing that this gene is stable and expressed only in cranberry leaves infected by phytoplasma ( Pradit et al, 2019b ). The primer used for the target gene is listed in Table 2 .…”

“…The primer used for the target gene is listed in Table 2 . The expression of actin was used as the endogenous control ( Rodriguez-Saona et al, 2013 ; De Lange et al, 2019 ; Pradit et al, 2019b ). The primers of the target gene and endogenous control were designed using PrimerQuest (Integrated DNA Technologies Inc., Skokie, Illinois, United States).…”

“… 1 Unknown “UnkPhyto” gene based on transcriptome data and RT-qPCR data from Pradit et al (2019b) . 2 Endogenous control gene.…”

“…To test whether the four synthetic elicitors of plant defenses reduce expression of a phytoplasma-specific marker gene, leaves 1 http://agsci.psu.edu/aasl from vines were taken from three randomly selected elicitortreated and untreated plants on June 17, 2019 (Figure 1; n = 5 treatments × 3 replicates = 15 plants) and stored at −80°C until used for real-time quantitative PCR (RT-qPCR) analysis. Total RNA was extracted from the leaves immediately after harvest via previously described methods (Rodriguez-Saona et al, 2013;De Lange et al, 2019;Pradit et al, 2019b). The total RNA extract was treated with Optizyme DNase I (Fisher Scientific, Hampton, New Hampshire, United States) to remove any residual DNA, suspended in 50 μl RNAse-free water, and quantified using a ND-1000 NanoDrop spectrophotometer.…”