Genetic Analysis Of An Arabidopsis Thaliana Mutant Susceptible To Phytophthora Sojae Infection

Resistance of entire plant species to all isolates of a microbial species is referred to as non-host resistance,which is the most common phenomena and is likely a durable form of plant resistance against pathogens. Nonhost plant resistance is considered to be closely related with the basal defense responses. In the past years, major progresses in understanding nonhost resistance include the significance of cell wall in the resistance responses, the identification of general elicitors such as the PAMPs (Pathogen Associated Molecular Patterns) that trigger plant defenses, and the cloning of some genes that are involved in the non-host resistance. The genetic basis of nonhost resistance is not clear though it was proposed that simultaneous recognition of a number of pathogen-derived molecules by multiple resistance genes is involved. Many nonhost resistance cases are mediated by active defense response which is similar to gene-for-gene resistance and single genes are therefore likely involved. Phytophthora species represent a unique group of plant pathogens called oomycetes that are evolutionally distant from true fungi and thus may have distinct genetic and biochemical mechanisms for interacting with host and nonhost plants. In this study Phytophthora sojae and Arabidopsis thaliana were employed to understand genetic basis of nonhost resistance in plants against oomycete pathogens. In the previous study, we identified an A. thaliana T-DNA insertional mutant 581-51 which is susceptible to P. sojae infection. By TAIL-PCR, the boundary sequences of all 4 T-DNA insertion sites (b,o,h,f) were cloned from the susceptible A. thaliana mutant 581-51. Sequence alignment showed that b,o,h genes are located on the Chromosome 4 and f on Chromosome 3. Individual mutants homozygous for b,o and f , respectively showed similar responses as that of wide type Col-0 to the infection by P. sojae. Genetic crosses between the mutant 581-51 and wild-type A. thaliana showed that all resulting F1 progenies are resistant to P. sojae, and Chi square test shows the segregation ratios (resistance-to-susceptibility) for eight independent F2 populations fit 3:1, suggesting a single recessive mutation. P. sojae. Further genetic and molecular characterization of this stable mutant will aid understanding of nonhost resistance in plant against oomycete pathogens.