UC Riverside

Phytophthora infestans, the causal agent of Irish potato famine (1840), continues to be one of the most devastating plant pathogens of potato and tomato. For completing their life cycle, every pathogen must acquire nutrients from its host organisms. Nutrient acquisition and metabolic adaptations are thus important characteristics of pathogen biology. Information about these aspects in the P. infestans-potato/tomato pathosystems was sought to help us better understand disease progression. To get an idea about the differentially expressed genes on different host tissues and axenically grown P. infestans, an RNA-seq experiment was performed. Several differentially expressed metabolic genes thus identified gave us some clues about the different microenvironments that the pathogen encounters during its in planta growth. Next, to understand how these metabolic genes are expressed in a time-dependent and spatial manner within the host tissues, a confocal microscopy-based approach was used. The proteins of genes coding for invertase activity, participating in sucrose breakdown, were demonstrated to localize within P. infestans haustoria. This is the first report of a metabolic gene being targeted to P. infestans haustoria, thus establishing the role of the latter in nutrient uptake in oomycete plant pathogens. Next, using confocal microscopy, the role of a phosphagen kinase system in energy transport was indirectly provided. The expression of differentially expressed genes depends on timely and coordinated process leading to stage-specific expression, which depends on the binding of specific transcription factors to their cognate transcription factor binding sites (TFBS). A combination of bioinformatics and molecular biology techniques was then used to identify ~100 putative TFBSs regulating the stage-specific expression of developmentally-regulated genes. An understanding of these aspects of pathogen biology may help us devise novel means to control the late blight disease.