PhD defence - Sixuan Zhao
Unravelling Plant Immune Mechanisms Through Forward Genetics
Assessment Committee
Associate Professor Fernando Geu-Flores, PLEN, University of Copenhagen, Denmark
Professor Stephan Wenkel, Umeå Plant Science Centre, Umeå University, Sweden
Senior Lecturer Laurence Bindschedler, School of Biological Sciences, University of London, Egham, UK
Supervisors
Professor Hans Thordal-Christensen, htc@plen.ku.dk
Place
Auditorium A1-01, Bülowsvej 17, 1870 Frederiksberg
The defence is followed by a reception in meeting room R322/23 on 3rd floor - Everybody is welcome
Ask for a copy of the thesis here: htc@plen.ku.dk
Summary
The plant immune system is highly complex, involving numerous signal pathways and biological activities. To investigate the genes involved in immune responses, mutants exhibiting altered immune phenotypes have been employed as valuable tools. During the investigation of gene functions, forward genetics serves as a powerful and versatile approach, as it uncovers the link between genes and phenotypes, and it as well as reveals relationships among different genes. In this thesis, three EMS mutant populations with the different genomic backgrounds, pen1-1 syp122-1, eds1-2, and eds1-2 ndr1-2 imm1-T, were utilized to identify genes or mutations involved in the diverse immune activities.
The lesion mimic mutant, pen1-1 syp122-1, is an effective tool to investigate the autoimmunity in plants. In this thesis, I screened a pen1-1 syp122-1 EMS mutant pool to identify genes participating in its autoimmune activities. In three rescued lines, r17-1, r18-2, and r19-3, the causal mutations were all identified through the Mutmap techniques to be in SSD6. This gene encodes a potential lipid transpfer protein, which binds onto the ER through a membrane anchoring domain, which was proven important for the functioning of SSD6 in previous mutant studies. In this study, I made subcellular localization studies to investigate the possible reasons for how a mutation causing the amino acid substitution, G463D in the membrane anchoring domain, influences the protein functions.
EDS1 is a crucial regulator for TNL-mediated immunity. In this thesis, an EMS mutant, B3Z5, in the eds1-2 line was studied. While B3Z5 has an intriguing resistance phenotype, challenges were encountered during the mapping and gene identification process. Characterizing the genetic mechanisms behind the B3Z5 line was very exciting, yet hinted by an unusual segregation ratio of 2:1. Two rounds of mapping with modified mapping strategies were performed to ultimately suggest two candidate causal genes.
The imm1A, in the eds1-2 background, was recently identified to confer resistance to various pathogens. In this thesis, we screened an eds1-2 ndr1-2 imm1A-T EMS mutant population to identify genes that specifically contribute to imm1A-mediated resistance. Different from other resistance screenings, which only select resistant mutants, we selected mutants with both enhanced and reduced resistance performance compared to the eds1-2 ndr1-2 imm1A-T original plants. Numerous interesting mutant lines were selected, and the mapping populations were generated to further identify interesting genes.