RESUMO
Certain plant-associating bacteria produce ice nucleation proteins (INPs) which allow the crystallization of water at high subzero temperatures. Many of these microbes are considered plant pathogens since the formed ice can damage tissues, allowing access to nutrients. Intriguingly, certain plants that host these bacteria synthesize antifreeze proteins (AFPs). Once freezing has occurred, plant AFPs likely function to inhibit the growth of large damaging ice crystals. However, we postulated that such AFPs might also serve as defensive mechanisms against bacterial-mediated ice nucleation. Recombinant AFP derived from the perennial ryegrass Lolium perenne (LpAFP) was combined with INP preparations originating from the grass epiphyte, Pseudomonas syringae. The presence of INPs had no effect on AFP activity, including thermal hysteresis and ice recrystallization inhibition. Strikingly, the ice nucleation point of the INP was depressed up to 1.9°C in the presence of LpAFP, but a recombinant fish AFP did not lower the INP-imposed freezing point. Assays with mutant LpAFPs and the visualization of bacterially-displayed fluorescent plant AFP suggest that INP and LpAFP can interact. Thus, we postulate that in addition to controlling ice growth, plant AFPs may also function as a defensive strategy against the damaging effects of ice-nucleating bacteria.
Assuntos
Proteínas Anticongelantes/química , Proteínas da Membrana Bacteriana Externa/química , Lolium/química , Proteínas de Plantas/química , Pseudomonas syringae/química , Proteínas Recombinantes de Fusão/química , Proteínas Anticongelantes/genética , Proteínas Anticongelantes/metabolismo , Proteínas da Membrana Bacteriana Externa/genética , Proteínas da Membrana Bacteriana Externa/metabolismo , Bioensaio , Cristalização , Congelamento , Expressão Gênica , Gelo , Cinética , Lolium/genética , Lolium/metabolismo , Lolium/microbiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Pseudomonas syringae/genética , Pseudomonas syringae/crescimento & desenvolvimento , Pseudomonas syringae/metabolismo , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , TemperaturaRESUMO
Genetic polymorphisms are the basis of the natural diversity seen in all life on earth, also in plant-pathogen interactions. Initially, studies on plant-pathogen interaction focused on reporting phenotypic variation in resistance properties and on the identification of underlying major genes. Nowadays, the field of plant-pathogen interactions is moving from focusing on families of single dominant genes involved in gene-for-gene interactions to an understanding of the plant immune system in the context of a much more complex signaling network and quantitative resistance. Simultaneously, studies on pathosystems from the wild and genome analyses advanced, revealing tremendous variation in natural plant populations. It is now imperative to place studies on genetic diversity and evolution of plant-pathogen interactions in the appropriate molecular biological, as well as evolutionary, context.