Defence and signalling in Potato-Phytophthora infestans interactions

Abstract: Potato is one of the major food crops and its yield is severely affected by late blight disease caused by Phytophthora infestans. P. infestans has the ability to manipulate plant defence signalling by secreting effector molecules causing so called effector triggered susceptibility. Some plants can recognize these effectors via resistance proteins that reactivate plant defence and lead to effector triggered immunity. This thesis discusses identification and analysis of field-pathological relevant potato material for resistance against P. infestans. The two selected potato clones were shown to be resistant, in fields with diverse P.infestans populations, and in growth chambers with a highly virulent Swedish P.infestans strain. They have slightly different resistance reaction at phenotypic and molecular level. One of the two resistant potato clones (SW93-1015) showed an unusual reduction in hypersensitive reaction expansion and part of the induced defence system was constitutively expressed in this potato clone. These two resistant potato clones and the susceptible cultivar Desiree were studied by a combination of quantitative proteomics assisted with newly generated sequence data, and genome wide transcriptomics. A number of putative effector-targets in the potato secretome, often single members of large gene families were identified. These studies have also provided us with insight to components involved in successful plant defence amid hypersensitive response. By analysing crossing populations, a remarkably simple genetic resistance in the potato clone SW93-1015 was identified. We also present a primary global phosphoproteomics analysis that led to identification of novel phosphosites and phosphorylation of several P. infestans effectors. These findings lead us to a better understanding of plant pathogen interactions in field relevant systems and hopefully will allow us to create more tools to overcome this devastating crop disease.