Pathogenesis-Related Proteins and Their Transgenic Expression for Developing Disease-Resistant Crops: Strategies Progress and Challenges

Abstract

Various pathogenic microorganisms (such as fungi, bacteria, viruses and nematodes) affect plant viability and productivity. However, plants combat these pathogens by inducing their defense mechanism to sustain their fitness. The aggregation of pathogenesis-related (PR) proteins in response to invading pathogens is a crucial component of a plant’s self-defense mechanism. PR proteins induce innate resistance in plants through fungal cell wall disintegration, membrane permeabilization, transcriptional suppression, and ribosome inactivation. Earlier studies have demonstrated their crucial role in determining resistance against phytopathogens, making them a promising candidate for developing disease-resistant crop varieties. Plant genetic engineering is a potential approach for developing disease-resistant transgenic crops by employing several PR genes (thaumatin, osmotin-like proteins, chitinases, glucanases, defensins, thionins, oxalate oxidase, oxalate oxidases like proteins/germin-like proteins and LTPs). Furthermore, the overexpression of PR proteins enhances the resistance against phytopathogens. As a result, this chapter gives an overview of PR proteins, including their classification, functional characterization, signaling pathways, mode of action and role in defense against various phytopathogens. It also highlights genetic engineering advances in utilizing these genes singly or synergistically against various phytopathogens to impart disease resistance. Various challenges faced with the products of transgenic technology and synergistic expression of different groups of PR proteins were also discussed.

Pathogenesis-Related Proteins (PRs) with Enzyme Activity Activating Plant Defense Responses

“…During plant-pathogen interaction, a sophisticated signaling network results in gene induction to produce several molecules for plant defense. Among these molecules, several protein types are produced, including pathogen-related enzymes, such as glucanases, chitinases, peroxidases and ribonuclease [25]. These enzymes can be produced in trace amounts by healthy plants, but they may have increased levels in the face of a pathogen.…”

“…During pathogen infection, the RNase activity of PR10 proteins can cause a cytotoxic cell impact and inhibit pathogen growth, degrading the pathogen cell [45,[99][100][101][102]. This inhibition occurs mainly through ribonuclease penetration into the pathogen, with PR10 phosphorylation subsequently occurring, and consequently the destruction of pathogenic cell RNAs [25].…”

“…PRX, peroxidase; PRs, pathogen-related proteins; Chit, chitinase; ROS, reactive oxygen species; Phyx, phytoalexin; β-1,3-gluc, β-1,3-glucanases; Ethy, ethylene; JA, jasmonic acid; LRR-RLK, leucinerich repeat receptor-like protein kinase; NB-LRR, nucleotide-binding and leucine-rich repeat; RBPs, RNA-binding proteins; RIPs, ribosome-inactivating proteins. Antimicrobial activity [25,44] These proteins can have direct or indirect action in plant resistance against microorganisms. PR proteins can inhibit pathogen growth and/or spore germination, and can also act as antimicrobial agents, hydrolases, and proteinase inhibitors and perform other activities [45,46].…”

“…PR defense proteins are molecules with different molecular weights, ranging from 6 to 43 kDa. They are thermostable, soluble at pH < 3, and protease-resistant, thus contributing to quantitative changes in protein levels during defense responses [9,18,25]. It is believed that PR proteins are encoded, but it is only after the presence of a stimulus that they will be expressed in plants.…”

Genome-Wide Identification and Expression Profiling of Pathogenesis-Related Protein 1 (PR-1) Genes in Durum Wheat (Triticum durum Desf.)

“…Interestingly, they constitute about 5–10% of the total protein in leaves [ 12 ]. PR proteins have been classified into 19 different families based on their main properties such as their protein sequence similarities, enzymatic activities [ 13 ], pH (acidic or alkaline), antigen 5, cysteine-rich secretory proteins, and pathogenesis-related-1 (CAP) proteins [ 14 ]. Among the different PR classes, PR-1 proteins were the first discovered proteins and the most studied.…”