A Plant Bacterial Pathogen Manipulates Its Insect Vector's Energy Metabolism

Abstract

Insect-transmitted plant-pathogenic bacteria may alter their vectors' fitness, survival, behavior, and metabolism. Because these pathogens interact with their vectors on the cellular and organismal levels, potential changes at the biochemical level might occur. "Candidatus Liberibacter asiaticus" (CLas) is transmitted in a persistent, circulative, and propagative manner. The genome of CLas revealed the presence of an ATP translocase that mediates the uptake of ATP and other nucleotides from medium to achieve its biological processes, such as growth and multiplication. Here, we showed that the levels of ATP and many other nucleotides were significantly higher in CLas-infected than healthy psyllids. Gene expression analysis showed upregulation for ATP synthase subunits, while ATPase enzyme activity showed a decrease in ATPase activity. These results indicated that CLas stimulated Diaphorina citri to produce more ATP and many other energetic nucleotides, while it may inhibit their consumption by the insect. As a result of ATP accumulation, the adenylated energy charge (AEC) increased and the AMP/ATP and ADP/ATP ratios decreased in CLas-infected D. citri psyllids. Survival analysis confirmed a shorter life span for CLas-infected D. citri psyllids. In addition, electropenetrography showed a significant reduction in total nonprobing time, salivation time, and time from the last E2 (phloem ingestion) to the end of recording, indicating that CLas-infected psyllids were at a higher hunger level and they tended to forage more often. This increased feeding activity reflects the CLas-induced energetic stress. In conclusion, CLas alters the energy metabolism of its psyllid vector, D. citri, in order to secure its need for energetic nucleotides.IMPORTANCE Insect transmission of plant-pathogenic bacteria involves propagation and circulation of the bacteria within their vectors. The transmission process is complex and requires specific interactions at the molecular and biochemical levels. The growth of the plant-pathogenic bacteria in the hemolymph of their vectors indicated that the hemolymph contains all the necessary nutrients for their growth. In addition to nutrients, "Candidatus Liberibacter asiaticus" (CLas) can take up energetic nucleotides, such as ATP, from its vector, Diaphorina citri, using ATP translocase. In this study, we found that the CLas pathogen manipulates the energy metabolism of its insect vector. The accumulation of ATP in CLas-infected D. citri psyllids indicated that CLas induces ATP production to fulfill its need for this energetic compound. As a result of ATP accumulation, a shorter life span and altered feeding behavior were observed. These findings increase our knowledge of insect transmission of the persistent-circulative-propagative type of plant pathogens vectored by insects.KEYWORDS huanglongbing, Diaphorina citri, "Candidatus Liberibacter asiaticus," energy metabolism, ATP, adenylated energy charge, HPLC, electric penetration graph, electropenetrography

Concomitant Loss of the Glyoxalase System and Glycolysis Makes the Uncultured Pathogen “Candidatus Liberibacter asiaticus” an Energy Scavenger

“…As expected, "Ca. Liberibacter asiaticus" infection of psyllids and citrus raises the levels of host glycolysis, TCA cycle metabolites, respiration rates (39), and ATP content (45,46).…”

“…E. coli was grown in Luria-Bertani medium at 37°C. L. crescens and X. albilineans were cultured in BM7 medium (11) and Modified Wilbrink's medium (45), respectively, at 28°C. Genomic DNA from L. crescens and X. albilineans cells was extracted using the GenElute Bacterial Genomic DNA kit (Sigma-Aldrich, St. Louis, MO).…”

Molecular mechanisms behind the accumulation of ATP and H2O2 in citrus plants in response to ‘Candidatus Liberibacter asiaticus’ infection

“…This finding is consistent with a recent study suggesting that in the psyllid Las alters the host environment to enhance nutrient availability and increase ATP levels. 77 This leads to the intriguing possibility that Las may directly or indirectly increase the ATP level in plant tissues as well for subsequent importation through its translocase directly from its host. Thus, information provided in this study has revealed molecular and physiological mechanisms involved in the host response to HLB and potential new targets for control strategies.…”

Infection with phytopathogenic bacterium inhibits melatonin biosynthesis, decreases longevity of its vector, and suppresses the free radical‐defense

“…DNA from adult psyllids (5 biologic replicates of 5 insects/replicate) was extracted using potassium acetate buffer as described by Killiny et al . The extracted DNA was quantified using a Nano‐Drop 2000 spectrophotometer (Thermo Scientific) and adjusted to 100 ng μL −1 .…”

“…DNA from adult psyllids (5 biologic replicates of 5 insects/ replicate) was extracted using potassium acetate buffer as described by Killiny et al 57 The extracted DNA was quantified using a Nano-Drop 2000 spectrophotometer (Thermo Scientific) and adjusted to 100 ng μL −1 . Extracted DNA was used for RT-qPCR amplification using 16S rRNA primers HLBasf and HLBr, the probe HLBp, TaqMan PCR master mix, SYBR green PCR master mix, and the protocol described by Li et al 58 and Zhao et al 59 qPCR assay was performed in a 96-well plate using an ABI 7500 RT-qPCR system, and supplies were from Applied Biosystems (Foster City, CA, USA) as described by Killiny et al 57…”