Identification and characterisation of effector proteins from Zymoseptoria tritici

Plant pathogens are known to secrete a large number of secreted proteins termed as effectors into the host plant. These secreted effector proteins play role in the infection and manipulation of plant host defenses for aiding successful colonisation. The filamentous fungal pathogen Zymoseptoria tritici: an important pathogen of wheat, also secretes effectors that play key role during host colonisation. In this thesis, 50 Zymoseptoria tritici small secreted proteins (ZtSSPs) were identified which fulfilled all the effector characteristics including; (i) small size, (ii) presence of signal peptide, (iii) presence of cysteine residues, (iv) lack of transmembrane domain and (v) lack of functionally annotated domains. Out of these 50, 30 were cloned and characterised initially based on their ability to induce cell death in planta using a non-host plant. Five novel candidates that induce cell death in a non-host plant were selected and this cell death was shown to be independent of presence a signal peptide. All five ZtSSPs were also involved in activation of diverse defense marker genes and were found to be differentially upregulated during infection suggesting their diverse roles. One particular ZtSSP, ZtSSP2 is a well conserved effector across isolates and interacts with a wheat host ubiquitin protein. This wheat ubiquitin possess a RING finger E3 ligase domain and plays a key role in ubiquitin mediated cellular processes. The expression of wheat ubiquitin ligase showed that its expression is downregulated at early and late stages of Z. tritici infection, suggesting involvement of this ubiquitin in host defense responses. To explore different system for effector characterisation the grass B. distachyon was used as a non-host model to study non-host defense and the potential for Z. tritici effector screening. In conclusion secreted effectors of Z. tritici play a key role in host defense manipulation. This study on Z. tritici candidate effectors has provided the identification of a wheat host effector target and further insights into the plant-pathogen interaction between Z. tritici, host plant wheat as well as with the non-hosts N. benthamiana and B. distachyon.