Approximately two and a half percent of protein coding genes in Arabidopsis encode enzymes with known or putative proteolytic activity. Proteases possess not only common housekeeping functions by recycling nonfunctional proteins. By irreversibly cleaving other proteins, they regulate crucial developmental processes and control responses to environmental changes. Regulatory proteolysis is also indispensable in interactions between plants and their microbial pathogens. Proteolytic cleavage is simultaneously used both by plant cells, to recognize and inactivate invading pathogens, and by microbes, to overcome the immune system of the plant and successfully colonize host cells. In this review, we present available results on the group of proteases in the model plant Arabidopsis thaliana whose functions in microbial pathogenesis were confirmed. Pathogen-derived proteolytic factors are also discussed when they are involved in the cleavage of host metabolites. Considering the wealth of review papers available in the field of the ubiquitin-26S proteasome system results on the ubiquitin cascade are not presented. Arabidopsis and its pathogens are conferred with abundant sets of proteases. This review compiles a list of those that are apparently involved in an interaction between the plant and its pathogens, also presenting their molecular partners when available.

IPeach (Prunus persica L. Batsch) is an economically important crop in Hungary. Current production is in ca. 6000 ha of commercial orchards. In July 2017 samples from 2 to 14 year old peach trees (P. persica cvs. Royal Summer, Royal Time, Cresthaven, O’Henry and Redkal) showing leaf and fruit spot symptoms were collected in a 100 ha commercial orchard in Pest County, Hungary. Disease incidence on leaves ranged from a low of 80% relative humidity) but not on water-treated controls. The original pathogen was re-isolated from lesions of inoculated leaves and its identity was confirmed by duplex-PCR (Pothier et al. 2011). To our knowledge, this is the first confirmed report on occurrence of X. arboricola pv. pruni on P. persica in Hungary, previously identified only on Prunus salicina by local plant protection service and on P. armeniaca (Schwarczinger et al. 2017). Bacterial spot of stone fruits is one of the most significant diseases of Prunus species included in the EPPO A2 list of pests recommended for regulation for European Union members. Similar symptoms on peach and apricot were recently reported by growers from two neighboring counties, indicating pathogen spread. Therefore Xap could have a significant impact on peach production in Hungary. References: Ballard, E. L., et al. Plant Dis. 95:1109, 2011. Parkinson, N., et al. Int. J. Syst. Evol. Microbiol. 57:2881, 2007. Pothier, J. F., et al. J. Microbiol. Meth. 86:16, 2011. Schaad, N. W. et al. (eds.) Laboratory Guide for Identification of Plant Pathogenic Bacteria, 3rd ed. APS, St. Paul, MN., 2001. Schwarczinger, I., et al. Plant Dis. 101:1031, 2017.

In June 2018 leaf spot symptoms suggesting Xanthomonas arboricola pv. pruni (Xap) infection were detected on almond (Prunus dulcis) cv. ‘Fournat de Brezenaud’ and later, in October also on almond c...