Project description:BACKGROUND: The tomato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae), is a pest of solanaceous crops such as tomato (Solanum lycopersicum L.) in the U.S. and vectors the disease-causing pathogen ‘Candidatus Liberibacter solanacearum’. Currently, the only effective strategies for controlling the diseases associated with this pathogen involve regular pesticide applications to manage psyllid population density. However, such practices are unsustainable and will eventually lead to widespread pesticide resistance in psyllids. Therefore, new control strategies must be developed to increase host-plant resistance to insect vectors. For example, expression of constitutive and inducible plant defenses can be improved through selection. Currently, it is still unknown whether psyllid infestation has any lasting consequences on tomato plant defense or tomato plant gene expression in general. RESULTS: To characterize the genes putatively involved in tomato defense against psyllid infestation, RNA was extracted from psyllid-infested and uninfested tomato leaves (Moneymaker) three weeks post-infestation. Transcriptome analysis identified 362 differentially expressed genes. These differentially expressed genes were primarily associated with defense responses to abiotic/biotic stress, transcription/translation, cellular signaling/transport, and photosynthesis. These gene expression changes suggested that tomato plants underwent a reduction in plant growth/health in exchange for improved defense against stress that was observable three weeks after psyllid infestation. Consistent with these observations, tomato plant growth experiments determined that the plants were shorter three weeks after psyllid infestation. Furthermore, psyllid nymphs had lower survival rates on tomato plants that had been previously psyllid infested. CONCLUSION: These results suggested that psyllid infestation has lasting consequences for tomato gene expression, defense, and growth.

Project description:Purpose: The tomato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae), is a pest of tomato (Solanum lycopersicum) and potato (S. tuberosum) in the U.S. and vectors the disease-causing pathogen ‘Candidatus Liberibacter solanacearum’. Plants undergo physiological, transcriptomic, or epigenetic changes in order to mount a stronger, faster response against secondary challenges by previously perceived threats. This is called defense ‘priming’ and it likely has an impact on vectored disease transmission. Currently, it is still unknown whether or not psyllid infestation has any lasting consequences for tomato gene expression or defense. To characterize the genes potentially involved in tomato priming against psyllids, RNA was extracted from psyllid-primed and uninfested tomato (Moneymaker) leaves three weeks after infestation. Methods: RNA was extracted and sequenced from plants three weeks after psyllid infestation. Plants were either left alone (Control or C) or infested with psyllids (Primed or J1). Libraries were developed using the TruSeq RNA Library Prep Kit v2. Sequencing was performed on the Illumina PE HiSeq 2500 v4 platform. Processed sequences were uploaded to the CyVerse Discovery Environment computational infrastructure where bioinformatic analysis was performed using the Tuxedo Suite 2 workflow. Results: Illumina HiSeq sequencing of tomato cDNA libraries produced 132,428,443 total reads that met FastQC quality control criteria. 94.6% of all reads mapped to vSL3.0 of the S. lycopersicum genome. CuffDiff2 analysis identified 310 differentially expressed genes (DEGs) between control and psyllid-primed plants (q-value <0.01). Conclusions: A week-long infestation by a small number of B. cockerelli had lasting consequences for gene expression in tomato plants. Homologs of the DEGs were associated with 1) defense against abiotic and biotic stress, 2) growth and development, and 3) components of plant biology indirectly involved in plant growth and development such as homeostasis, transcription/translation, and molecular transport.

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