Targets are under so much pressure from effectors that McDowell & Simon 2006 expected
PBS1 to experience
diversifying selection. They looked forward to results finding little sequence affinity, an entire family of
PBS1s, and radiation across descendant plant species. However just a few years later
PBS1 was demonstrated by Caldwell and Michelmore 2009 to be one of the most
conserved proteins in all
flowering plants. Further, they found it to be so widespread that it must have yet-undiscovered function(s): It is found widely even in taxa with no RPS5 guard. They speculate that these other functions are so vital that PBS1 is being prevented from otherwise adapting to effectors - thus possibly dumping that evolutionary pressure onto the
nucleotide-binding leucine-rich repeat receptors guarding it instead. They also found this to make PBS1 an even more useful modifiable immune decoy, as it is recognized by a wider array of
convergently evolved immune proteins than just RPS5. ==Orthologs==