Y2H results present a parallel between the plant STP and the innate immunity in animals where the NF ??B/Rel family of transcriptional activator proteins exists as hetero- or homodimeric proteins. The animal pathway involves a multitude of transcription factors that interact with each other to elicit the immune response. Transcription factors c. Jun, NF???B, and c-Fos serve to activate the defense genes in animals. In plants, a family of closely related factor (group IIa WRKY factors) may function in place of the NF???B/Rel family. Additionally, Xb10 may serve as a master transcription factor that binds to other group IIa members to regulate genes.Hence, Signal transduction pathways may be evolutionarily conserved through the passage of time. Another protein, Xb3 (an E3 ubiquitin ligase that interacts with and is phosphorylated by Xa21) is similar to an animal counterpart TRAF6 (also an E3 ubiquitin ligase) and therefore may play a similar role) (Song et al., personal communication). The plant innate immunity receptor similar to Xa21, FLS2 (a receptor that responds to a bacterial protein flagellin), requires a MAP kinase signaling cascade. MAP kinase cascades are known to be required for signaling in animal innate immunity (Asai et al., 2002).
The plant system is not completely identical to that of animals, however: the mammal pathway has kinase intermediates to activate transcription factors after recognition, whereas the plant system appears to function through the direct interaction between Xa21 and Xb10.