R gene-mediated resistance in the management of plant diseases

Biotic stress factors cause massive damage to crops and account for major economic losses globally. With the global temperature on the rise, a great threat looms on the global economy and food security as sustainable agriculture is expected to be devastated by larger outbreaks of diseases worldwide. Plants have developed versatile counter-strategies to overcome these stressors. These strategies rely on preformed defense or induced defense responses which, in turn, entail a complex crosstalk among different signaling pathways. Once the presence of a pathogen is detected, the plant host switches on its defense response. Very specific recognition of the invading pathogen is mediated via the detection of their Avr effector proteins by the cognate elements in the plant host, i.e., the R proteins, encoded by R genes. Successful recognition of Avr by the cognate host R proteins sets distinct signaling cascade(s) into motion to activate defense responses. The nucleotide-binding leucine-rich repeat proteins (NB-LRRs or NLRs) represent the major class of R proteins and insights gained regarding their structural complexity and underlying signal transduction has enabled researchers to exploit them for competent introgression of disease resistance in plants against a single or a broad range of pathogens. In addition to conventional breeding, more recent biotechnological interventions have also been employed to develop plants with improved disease resistance with the use of R genes. The domain of R gene-mediated disease resistance has gained much attention from plant breeders and through experimental interventions, many promising opportunities for conferring resistance for effective management of diseases have come forth. This review attempts to summarize the progress made hitherto and focuses on how the knowledge base so created has been used to find out solutions to the major biotic problems occurring throughout the world.