Many phytopathogens secrete and/or inject 'effector' proteins inside host cells to modulate cellular processes. Phytopathogens deliver effector proteins inside host plant cells to promote infection. Crystal structures of the effector domains from two oomycete RXLR proteins, Phytophthora capsici AVR3a11 and Phytophthora infestans PexRD2 reveal a core alpha-helical fold (termed the 'WY-domain') which enables functional adaptation of these fast evolving effectors through (i) insertion/deletions in loop regions between alpha-helices, (ii) extensions to the N and C termini, (iii) amino acid replacements in surface residues, (iv) tandem domain duplications, and (v) oligomerization. It is proposed that the core fold provides both a degree of molecular stability and plasticity that enables development/maintenance of effector virulence activities while allowing evasion of recognition by the plant innate immune system during rapid 'arms race' co-evolution [1].

1: Structures of Phytophthora RXLR effector proteins: a conserved but adaptable fold underpins functional diversity. Boutemy LS, King SR, Win J, Hughes RK, Clarke TA, Blumenschein TM, Kamoun S, Banfield MJ; J Biol Chem. 2011;286:35834-35842. PMID:21813644