| Popis: |
Plant pathogens secrete effector proteins that modulate host processes, thereby enabling parasitic colonization. The RXLR cytoplasmic effector AVR3a of Phytophthora infestans confers avirulence on potato plants carrying the R3a gene. Similar to other oomycete effectors, AVR3a carries a signal peptide followed by a conserved motif centered on the consensus RXLR sequence that is functionally similar to a host cell-targeting signal of malaria parasites. In this thesis research, AVR3a activity and its relation to P. infestans infection was investigated. We found that in addition to its avirulence activity, AVR3aKI suppressed cell death induced by the INF1 elicitin of P. infestans. Deletion analyses showed that the C-terminal domain of AVR3a is sufficient for effector activities. High-throughput saturated mutant screens for R3a activation identified 136 AVR3aEM gain of function mutants, but only 13 AVR3aKI loss of function mutants. Our findings support a model wherein recognition of AVR3a by R3a most likely involves the interaction with a host protein rather than an enzymatic activity. Most AVR3a EM gain of function mutants did not suppress cell death suggesting that distinct amino acids of AVR3a condition R3a hypersensitivity and cell death suppression. Functional analyses of AVR3a homologs from P. infestans, P. sojae and P. capsici showed that R3a activation, but not cell death suppression, was conserved among several homologs from different species. Therefore, recognition by R3a is a more widespread activity of the AVR3a family in Phytophthora than cell death suppression. Overall these studies improved our understanding of the function, structure and evolution of AVR3a. |
