Pathogenesis-related (PR) proteins are proteins produced in plants in the event of a pathogen attack.[1] They are induced as part of systemic acquired resistance. Infections activate genes that produce PR proteins. Some of these proteins are antimicrobial, attacking molecules in the cell wall of a bacterium or fungus. Others may function as signals that spread “news” of the infection to nearby cells. Infections also stimulate the cross-linking of molecules in the cell wall and the deposition of lignin, responses that set up a local barricade that slows spread of the pathogen to other parts of the plant.[2]
Many pathogenesis-related protein families also coincide with groups of human allergens, even though the allergy may have nothing to do with the defense function of the proteins.[5] Grouping these proteins by their sequence features allows for finding potential allergenic proteins from sequenced plant genomes, a field of study dubbed "allergenomics".[6]
Classification
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As of 2014[update], 17 families of PR proteins have been named:[5]
Different PR-protein families and allergens identified
Bet v 1 (birch pollen)— allergic rhinoconjunctivitis and asthma
Pru av 1 (cherry), Mal d 1 (apple), Api g 1 (celery), and Dau c 1 (carrot)—oral allergy syndrome
Gly m 4 (soy), Vig r 1 (mung bean), Cor a 1 (hazelnut), and Cas s 1 (chestnut), Act c 8 (golden kiwi fruit), Act d 8 (green kiwi fruit) —oral allergy syndrome
Pru p 3 (peach), Mal d 3 (apple), Pru av 3 (cherry), Pru ar 3 (apricot), Cor a 8 (hazelnut), Cas s 8 (chestnut), and Zea m 14 (maize)—oral allergy syndrome
As PR proteins are produced when plant tissue is stressed, various ways of stress signaling is used to "bait" the plant into expressing PR genes for identification. Useful stressors include an actual infection or simply defense signals such as salicylate and methyl jasmonate. The proteins can be identified by isolation, peptide digestion, and matching against the genomic sequences (protein sequencing). The sequences obtained can then be checked against known PR protein families for categorization.[8][9]
^Waters EJ, Shirley NJ, Williams PJ (1996). "Nuisance Proteins of Wine Are Grape Pathogenesis-Related Proteins". Journal of Agricultural and Food Chemistry. 44 (1): 3–5. doi:10.1021/jf9505584.
This article incorporates text by Mau Sinha, Rashmi Prabha Singh, Gajraj Singh Kushwaha, Naseer Iqbal, Avinash Singh, Sanket Kaushik, Punit Kaur, Sujata Sharma, and Tej P. Singh available under the CC BY 3.0 license.