Plant Innate Immune Response: Qualitative and Quantitative Resistance

Abstract

Plant diseases, caused by microbes, threaten world food, feed, and bioproduct security. Plant resistance has not been effectively deployed to improve resistance in plants for lack of understanding of biochemical mechanisms and genetic bedrock of resistance. With the advent of genome sequencing, the forward and reverse genetic approaches have enabled deciphering the riddle of resistance. Invading pathogens produce elicitors and effectors that are recognized by the host membrane-localized receptors, which in turn induce a cascade of downstream regulatory and resistance metabolite and protein biosynthetic genes (R) to produce resistance metabolites and proteins, which reduce pathogen advancement through their antimicrobial and cell wall enforcement properties. The resistance in plants to pathogen attack is expressed as reduced susceptibility, ranging from high susceptibility to hypersensitive response, the shades of gray. The hypersensitive response or cell death is considered as qualitative resistance, while the remainder of the reduced susceptibility is considered as quantitative resistance. The resistance is due to additive effects of several resistance metabolites and proteins, which are produced through a network of several hierarchies of plant R genes. Plants recognize the pathogen elicitors or receptors and then induce downstream genes to eventually produce resistance metabolites and proteins that suppress the pathogen advancement in plant. These resistance genes (R), against qualitative and quantitative resistance, can be identified in germplasm collections and replaced in commercial cultivars, if nonfunctional, based on genome editing to improve plant resistance.

Molecular breeding technologies and strategies for rust resistance in wheat (Triticum aestivum) for sustained food security

“…An adequate level of resistance that is durable is the most desired characteristic in crop breeding. Quantitative resistance, often governed by several genes, provides durable resistance and hence is recognized by breeders as a valuable approach for protecting crops (Niks et al ., ; Kushalappa et al ., ). In general, two classes of genes govern the genetics of resistance in wheat, race‐specific resistance ( R ) genes and non‐race‐specific resistance genes (that often confer slow‐rusting resistance).…”

Unraveling the molecules hidden in the gray shadows of quantitative disease resistance to pathogens

“…Therefore, the quantitative counterpart may have missing components. The missing concept here not necessarily corresponds to complete absence of a particular component, but to differential quantities of resistance related metabolites, proteins coded by R genes, or PRRs, which in turn are regulated by other genes (Kushalappa et al, 2016). Therefore, the more defense-related components are missing (or diminished), the more resistance is reduced.…”

“…In this way, resistance known as qualitative could also be polygenic and be achieved if all the components are present and function correctly (Kushalappa et al, 2016). Therefore, the quantitative counterpart may have missing components.…”

“…One interpretation of how QDR works at the cellular level considers QDR as corresponding weak PTI or ETI (López, 2011;Kushalappa et al, 2016). In this way, resistance known as qualitative could also be polygenic and be achieved if all the components are present and function correctly (Kushalappa et al, 2016).…”

Identification of Rehmannia glutinosa L. NB-ARC family proteins and their typical changes under consecutive monoculture stress

“…The results suggested that the imbalance of the rhizosphere microecology probably is one important cause for the formation of consecutive monoculture problems in R. glutinosa. Modern plant immunology and molecular biology studies have showed that pathogen infection is closely related to the false response of host plant immune defence system (Smith et al 2014;Kushalappa et al 2016). Previous studies have demonstrated that core biological processes, including DNA replication, RNA transcription and protein translation, are significantly damaged in consecutive monocultures of R. glutinosa.…”