Exploiting Broad-Spectrum Disease Resistance in Crops: From Molecular Dissection to Breeding

Abstract

Plant diseases reduce crop yields and threaten global food security, making the selection of disease-resistant cultivars a major goal of crop breeding. Broad-spectrum resistance (BSR) is a desirable trait because it confers resistance against more than one pathogen species or against the majority of races or strains of the same pathogen. Many BSR genes have been cloned in plants and have been found to encode pattern recognition receptors, nucleotide-binding and leucine-rich repeat receptors, and defense-signaling and pathogenesis-related proteins. In addition, the BSR genes that underlie quantitative trait loci, loss of susceptibility and nonhost resistance have been characterized. Here, we comprehensively review the advances made in the identification and characterization of BSR genes in various species and examine their application in crop breeding. We also discuss the challenges and their solutions for the use of BSR genes in the breeding of disease-resistant crops.

Distribution of Bacterial Blight Resistance Genes in the Main Cultivars and Application of Xa23 in Rice Breeding

“…Among these genes, Xa21 , Xa23 , and the un-cloned R gene Xa7 act in a dominant manner and confer the strongest resistance to BB with the broadest resistance spectrum ( Zhang, 2009 ; Chukwu et al, 2019 ). Recently, many R genes for BB were successfully incorporated into both elite inbred varieties and parental lines of hybrid rice to control the disease using MAS ( Chukwu et al, 2019 ; Jiang et al, 2020 ; Li W. et al, 2020 ). Notably, a few of those R genes, such as Xa3 , Xa4 , Xa7 , and Xa21 , have been widely utilized in rice resistance breeding since the 1980s ( Deng Q. et al, 2006 ; Zhang, 2009 ; Chen et al, 2011 ; Luo et al, 2012 ).…”

When a knockout is an Achilles’ heel: Resistance to one potyvirus species triggers hypersusceptibility to another one in Arabidopsis thaliana

“…Plant pathogens are responsible for significant agricultural and economic losses worldwide (Li et al, 2020). Genetic resistance is an important trait looked for in crop improvement programmes as it provides an effective and environmentally safe strategy to control pathogens in fields.…”

Fatty Acid Desaturases in the Chloroplast and Endoplasmic Reticulum Promote Susceptibility to the Green Peach AphidMyzus persicaeinArabidopsis thaliana

“…These so-called "stealthy" herbivores can evade many of the plant defenses normally triggered by insect damage, although they induce a variety of reactions that overlap with plant defenses against pathogens (Kaloshian and Walling 2005;Walling 2008). In addition to constitutive and induced defenses, the success of invaders such as pathogens or aphids is also influenced by socalled susceptibility factors, or host traits that can promote the infestation process (Eckhart 2002;Li et al 2020;van Schie and Takken, 2014). Because of their key role in modulating immunity, susceptibility factors are common targets for genome editing and other approaches to engineer enhanced disease resistance in crops (Zaidi et al, 2018).…”

“…Without proper regulation by other genes, receptors for pathogen detection or immune signaling and defense genes often cause excessive cell death and stunted growth in plants (Ning et al 2017). In the absence of infection, negative regulators limit these costs to plant growth by suppressing expression of immune genes or mediating degradation of their protein products; however, in the presence of a virulent pathogen that is not effectively recognized by the host plant, these negative regulators can also function as susceptibility factors, impeding appropriate immune responses (Li et al 2020;van Schie and Takken, 2014). For example, NRL1 in potato suppresses cell death by promoting proteolysis of a positive regulator of immunity (SWAP70), and it promotes infection by virulent strains of the late blight pathogen Phytopthora infestans that express the Pi02860 effector protein because Pi02860 causes NRL1 to degrade SWAP70 even in the presence of the pathogen (He et al 2018).…”

“…For example, NRL1 in potato suppresses cell death by promoting proteolysis of a positive regulator of immunity (SWAP70), and it promotes infection by virulent strains of the late blight pathogen Phytopthora infestans that express the Pi02860 effector protein because Pi02860 causes NRL1 to degrade SWAP70 even in the presence of the pathogen (He et al 2018). Another example of a susceptibility factor is the SSI2 fatty acid desaturase (FAD) in rice which promotes infection by the causal agents of leaf blight and blast (Jiang et al 2009;Li et al 2020). Interestingly, loss of function of SSI2 in Arabidopsis reduces susceptibility to the green peach aphid, Myzus persicae (Pegadaraju et al 2007;Louis et al 2010a), and Fatty Acid Desaturase 7 (FAD7) also promotes susceptibility to aphids in Arabidopsis and tomato (Avila et al 2012).…”