Plant immunity and pathogen interfering mechanisms: effectors and bodyguards.

There is an arm race between plants and their pathogens, by fungi, and bacteria, as well as between plants and insects. Plant proteases are hydrolytic enzymes, grouped on the basis of the catalytic amino acid, as serine, cysteine, aspartic acid, or metal dependent activity. Plant-fungi interactions, as well as plants with other invaders, have been elucidated in recent years, showing an evolutionary adaptation of hosts and invaders to produce proteases and evolve new protease inhibitors. Interactions between protease inhibitors and the target proteases provide information on the ways organisms interact and defend themselves from pathogens, recognizing symbionts from parasite organisms. A comparative analysis of protease inhibitors in plants with sequenced genomes have been recently performed. In the analysis of PIs, protease biochemical assays, protein-protein interaction studies and protease chips were used to analyze constitutive and inducible inhibitors under different conditions. Recently, activity-based protease profiling (ABPP) was used to differentiate enzymes tissue specificity, and roles in various physiological and pathological states. Specificities of PIs toward different protease (serine and cysteine proteases) can allow to selectively and differentially bind and detect various proteases. In this review we summarize the most recent knowledge on plant pathogens and the mechanisms they evolved to circumvent plant defences among which pathogen effectors, proteases and proteases inhibitors. Finally, we introduce the recent findings on pathogen bodyguards, proteins interfering with plant defence mechanisms or decoys, mimicking Transcription Activator Like Effectors (TALE). It is envisaged that further advances in understanding the function of pathogen effectors will provide new ways to improve plant immunity and mechanisms of defence against their pests.