1a. Objectives (from AD-416):
To determine the differences in potato psyllid gene expression in psyllids harboring Liberibacter solanacearum reared at different temperatures.
1b. Approach (from AD-416):
DNA sequencing of psyllid ESTs, annotation, and organization in a PAVE database for mining. Documents SCA with U of AZ.
3. Progress Report:
This project studies the transmission and effects of the zebra chip bacterium on potato psyllids which contributes to Objective 2 of the in-house project; "Determine host resistance options, epidemiological parameters and develop diagnostic tests for emerging pests and pathogens of potato". The potato psyllid, Bactericera cockerelli, transmits the bacterium Candidatus Liberibacter solanacearum (CLso) to pepper, potato, and tomato crops. This bacterium causes the “zebra chip” (ZC) disease in potatoes and vein-greening of tomato and pepper plants. In ZC affected potatoes, severe discoloration occurs in the tuber flesh severely reducing potato chip and French fry quality. ZC symptom progression in potato plants and potato psyllid biology are both affected by temperature. We are seeking insights into how temperature differences influence psyllid gene expression and psyllid physiological processes. To do this, total RNA was extracted from CLso-infected and uninfected psyllids reared at 18C, 24C and 30C from which 48 Illumina paired-end libraries were constructed. Each library was sequenced separately. When transcript profiles were compared at the ‘optimal growth’ temperature of 24C for both CLso-infected and uninfected treatments, the number of RNA transcripts having a 4-fold change in gene expression was higher for psyllids reared at 30C compared to those at 18C. Quantitative PCR analysis showed that bacterial titer of psyllids reared at 18C and 24C had similar levels, which was lower compared to those at 30C suggesting that an increase in temperature increases bacterial titer in psyllids. These results support recent findings in which potato plants reared at higher temperatures showed ZC symptoms faster and died quicker. Additionally, a number of transcripts putatively involved in psyllid host development and in CLso pathogenesis have been validated by reverse-transcriptase polymerase chanin reaction.