The effect of genetic variation on the immune response to Pseudomonas syringae pv. tomato strain dc3000 of Arabidopsis Sf2 plants

Abstract

All organisms are exposed to pathogens at one time or another. Plants possess an immune system consisting of disease resistance genes that allows them to fight off bacterial infections, and sickness. Among these genes is the RPS4 gene. The Arabidopsis RPS4 gene provides gene for gene specific resistance to Pseudomonas syringae pv. tomato strain DC3000 expressing the avirulence gene avrRps4. On the RPS4 protein there are two amino acid changes that are of interest. The first change is at position 195 from Asparagine to Aspartic acid, and the second change is at position 950 from Tyrosine to Histidine. When only the change at position 195 is present , there is total loss of function. When only the change at position 950 is present, there is loss of function, but not as severe as when the change at position 195 is present. When both changes are present, there is total loss of function. This most probably means that the change at N195 is most significant. However in the ecotype known as Sf2, with this change present, the plant is still very resistant to DC3000. Though the reasons for this phenomenon are unknown one possible theory is that a resistance gene other than RPS4 recognizes DC3000 in the Sf2 ecotype. Consequently the inactivity of the RPS4 gene by this amino acid change would not affect the plants response to DC3000, because it is another gene that provides the immune response to it.