Table 1.

Pathogenesis-Related Proteins (sPRs) properties and roles in plant defense.

Family	Properties/Functions	References
PR-1 (11a, 1b and 1c)	Abundant proteins in the apoplast during plant–pathogen interaction Inhibit pathogens Antifungal and antivirus activity Metal tolerance	[11,12,13,14,15,16,17]
PR-2 (Classes: I, II, and III)	Plant cell wall (β-1,3-glucan hydrolysis) Antibacterial, antifungal and antivirus activity	[15,18,19,20]
PR-3; PR-4; PR-8; PR-11 (Classes: I, II, IV, V, VI, and VII)	Plant cell wall (Chitin hydrolysis) Antibacterial and antifungal activity Salt tolerance	[15,18,20,21]
PR-5	Similarities with thaumatin Antifungal activity Cause osmotic rupture of fungal plasma membrane	[18,22,23]
PR-6	Protease inhibitors Cleave exopeptidases produced by bacteria, fungus and insects	[24,25,26]
PR-7	Endoproteases Mechanism of action is understudied Might be antimicrobial (pathogen cell wall degradation)	[25,26,27]
PR-9	Peroxidase activity Catalyze the oxidation of hydrogen peroxide on substrates (organic and inorganic)	[28,29]
PR-10	Ribonucleases—degrade RNA Programmed cell death during hypersensitivity reaction Antibacterial, antifungal, antinematode and antivirus activity Slat and cold stress tolerance	[20,30,31,32]
PR-12	Defensins Produced constitutively in plant structures (leaves, flowers, tubers, pods and seeds) Increased abundance during plant–pathogen interaction Antibacterial activity	[15,18,26]
PR-13 (Classes: I, II, III and IV)	Thionins—bacterial membrane lysis Distributed in the plant cell wall, vacuole and protein bodies Defense against a wide range of pathogens	[26,33,34,35,36]
PR-14	Nonspecific lipid transfer proteins (ns-LTPs)—cuticle synthesis Secreted and are associated with plant cell wall Defense against a wide range of pathogens	[26,37,38,39]
PR-15; PR-16	Oxalate oxidase and oxalate-oxidase-like protein (OLP’s), respectively Generation of ROS immediately after pathogen attack, which has antimicrobial activity	[25,26,40,41]
PR-17	Similarities with aminopeptidase (such as that found in eukaryotes and bacteria) Secretory protein Proteolytic activity Antifungal and antiviral activity	[18,25,42]
PR-18	Carbohydrate oxidases properties Substrate specificity resulting in hydrogen peroxide as one of the reaction products Antibacterial activity	[25,43]
PR-19	Biological role is not deciphered yet Antimicrobial activity	[25,44]