Regulation of Las transmission and microbial colonization by the Asian citrus psyllid immune system

Regulation of Las transmission and microbial colonization by the Asian citrus psyllid immune system

Report Date: 04/21/2017
Project: 15-021   Year: 2017
Category: ACP Vector
Author: Kirsten Pelz-Stelinski
Sponsor: Citrus Research and Development Foundation

Obj. 4. The purpose of this objective is to determine whether prior pathogen or dsRNA exposure inhibits Las acquisition by psyllids. We investigated if D. citri exhibits immune priming and produces a different response to secondary infections and the specificity of that protection. To force D. citri to consume bacteria, they were held on an artificial feeding sachet. The artificial feeding sachet was constructed from a petri dish (35 mm x 10 mm) with the bottom removed and covered with thinly-stretched Parafilm (Bemis NC, Neenah, WI). A and two pieces of thinly stretched Parafilm (Bemis NC, Neenah, WI) with a filter paper disc (2.6 cm dia) with 300 �l of diet solution was placed on the Parafilm and covered with an additional Parafilm layer (Russell and Pelz-Stelinski, 2015). The diet solution consisted of 17% sucrose in deionized, distilled water, 30 �l/ml of neon green food coloring (McCormick & Company, Inc., Sparks, MD). Total bacteria concentration in diet was 1e7 cells/ml. Diet solutions were placed in a dry heat block at 95�C for 15 min, shaken after 7 min to kill bacteria, and stored at -20�C until used. Diet solutions were plated on nutrient agar plates and incubated at 37�C for 24 to ensure bacteria were not viable. For the duration of the trials, feeding sachet were placed in clear, acrylic 85 mm x 70mm x 30 mm boxes and held in an environmentally-controlled chamber (description of incubator) at 16:8 hr light:dark cycle, 27�2�C, and 60-65% RH. Between 15-25 adult, unmated, sex-separated D. citri were primed by placing them on feeding sachets for 4 days. Surviving D. citri were moved to a second sachet containing 1e6 cells/mL live S. marcescens where they remained until all D. citri were dead. Mortality was recorded once daily. Transgenerational immune priming bioassays were conducted with psyllids placed on artificial diets containing heat inactivated E. coli, M. luteus, or no bacteria. To force D. citri to consume bacteria, they were held on an artificial feeding sachet. The artificial feeding sachet was constructed from a petri dish (35 mm x 10 mm) with the bottom removed and covered with thinly-stretched Parafilm (Bemis NC, Neenah, WI). A and two pieces of thinly stretched Parafilm (Bemis NC, Neenah, WI) with a filter paper disc (2.6 cm dia) with 300 �l of diet solution was placed on the Parafilm and covered with an additional Parafilm layer (Russell and Pelz-Stelinski, 2015). The diet solution consisted of 17% sucrose in deionized, distilled water, 30 �l/ml of neon green food coloring (McCormick & Company, Inc., Sparks, MD). Total bacteria concentration in diet was 1e7 cells/ml. Diet solutions were placed in a dry heat block at 95�C for 15 min, shaken after 7 min to kill bacteria, and stored at -20�C until used. Diet solutions were plated on nutrient agar plates and incubated at 37�C for 24 to ensure bacteria were not viable. For the duration of the trials, feeding sachet were placed in clear, acrylic 85 mm x 70mm x 30 mm boxes and held in an environmentally-controlled chamber (description of incubator) at 16:8 hr light:dark cycle, 27�2�C, and 60-65% RH. Between 15-25 adult, unmated, sex-separated D. citri were primed by placing them on feeding sachets for 4 days. Data presented here are preliminary, as additional replicates were collected during February and March 2017. These insects are currently being processed and analyzed via QPCR. Offspring of female D. citri that were fed a diet containing M. luteus (n = 17, 2.60E7 � 1.35E7) or E. coli (n = 18, 2.09E6 � 8.40E5) had higher CLas titers than offspring of non-primed females (n = 8, 1.22E5 � 6.20E4). The Ct of plant material was correlated with the titer of CLas in D. citri (b = -0.140, F1,41 = 4.115, p = 0.050, R2 = 0.09). Previously, we demonstrated that the D. citri immune response is induced due to recognition of Gram-positive bacteria, such as M. luteus. Given that M. luteus protected D. citri from S. marcescens, and CLas is also a Gram-negative bacterium, it was expected that CLas titers would be lower in offspring of M. luteus primed adults. In fact, the opposite was observed. Females fed a diet containing M. luteus prior to mating had higher CLas titers and produced offspring that acquired CLas at a much higher rate than those from control or E. coli fed females. This suggests that immune priming with M. luteus infection may facilitate CLas infection.


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