''AvrPphB SUSCEPTIBLE 1/PBS1'' is a protein kinase acting upon

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − form un ...

and

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO� ...

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/ref> It is a receptor-like cytoplasmic kinase, of Subfamily VII. It is the guardee of ''

RESISTANCE TO PSEUDOMONAS SYRINGAE 5 Resistance may refer to: Arts, entertainment, and media Comics * Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm: ** Resistance (comics), ''Resistance'' (comics), based on the video game of th ...

/RPS5''. PBS1 is cleaved by an effector, AvrPphB, used by ''Pseudomonas syringae'' pv. ''phaseolicola'', serving as an immunological decoy to signal RPS5 that an attack is underway as reviewed by Kourelis et al. 2016.

Evolutionary history

Targets are under so much pressure from effectors that McDowell & Simon 2006 expected ''PBS1'' to experience

diversifying selection Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population ...

. They looked forward to results finding little sequence affinity, an entire family of ''PBS1''s, 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

One model and many economic plants are known to have multiple orthologs per genome: * ''At''PBS1 - in the model ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...

'' :* ''At''PBS1 - with a 5- Alanine insertion to produce a gape in the cleavage site, falsely mimicking constant cleavage by the effector * ''Gm''PBS1 - in '' Glycine max'' :* ''Gm''PBS1–1 ::* ''Gm''PBS1–1 - same results as the 5xAla ''At''PBS1 above :* ''Gm''PBS1 - against

Soybean Mosaic Virus Soybean mosaic virus (SMV) is a member of the plant virus genus ''Potyvirus'' (family Potyviridae). It infects mainly plants belonging to the family Fabaceae but has also been found infecting other economically important crops. SMV is the cause o ...

* PBS1 - against the Type-III effector of AvrRpt2 produced by '' P. syringae'' * PBS1 - against the Nla protease produced by the Tobacco Etch Virus (TEV) * PBS1 - against the Nla protease produced by the Turnip Mosaic Virus (TuMV)

Future research

Indiana University (home of Pottinger and Innes) is prosecuting a family of patents for the RPS5-PBS1 decoy system. In the future it is expected that modified PBS1 decoys will become cheaper and easier to make as unrelated molecular genetics technologies improve. This system will only be deployable against effectors which act intracellularly within the host, as PBS1 is not located in any extracellular locations. The determination of the structure of ZAR1 has been useful in understanding NLRs in general, and that information will continue to be applied to understand and develop PBS1s.

References

{{Plant-disease-stub Plant genes Arabidopsis thaliana genes