UC Riverside

Phytophthora infestans causes the late blight disease of potato and tomato. Spores of Phytophthora are important for dissemination and causing infection. In this thesis, I studied several aspects of Phytophthora spore biology. (1) I performed RNA-seq of sporangia from rye media, potato leaflets, tomato leaflets, and potato tuber slices to investigate whether sporangia from artificial media and from plants are functionally equivalent. I found that sporangia from these different sources had only modest differences in transcriptional profiles, but showed similar infection potential using single-zoospore infection assays. This is an important piece of information indicating that spores from artificial media are good models for the natural situation. (2) I studied a MADS-box transcription factor to understand the regulation of sporangia development in P. infestans. MADS was shown to regulate many sporulation-induced genes, to act before previously known regulators, and to be regulated both at the transcriptional and post-translational levels. (3) I checked for potential artifacts associated with the homology-based gene silencing method that is commonly used to study gene function in Phytophthora. Based on studies of two target genes, the cis-spread of silencing was frequently observed within 500 nt distance of the target gene; however, this did not occur in all transformants generated by the same silencing vector. This suggests that the expression of neighboring genes should be checked to ensure that phenotypes assigned to genes based on silencing data are reliable.