The Arabidopsis pattern recognition receptor EFR enhances fire blight resistance in apple

Abstract

Fire blight disease, caused by the bacterium Erwinia amylovora (E. amylovora), is responsible for substantial losses in cultivated apples worldwide. An important mechanism of plant immunity is based on the recognition of conserved microbial molecules, named pathogen-associated or microbe-associated molecular patterns (PAMPs or MAMPs), through pattern recognition receptors (PRRs), leading to pattern-triggered immunity (PTI). The interspecies transfer of PRRs represents a promising strategy to engineer broad-spectrum and durable disease resistance in crops. EFR, the Arabidopsis thaliana PRR for the PAMP elf18 derived from the elongation factor thermal unstable (EF-Tu) proved to be effective in improving bacterial resistance when expressed into Solanaceae and other plant species. In this study, we tested whether EFR can affect the interaction of apple with E. amylovora by its ectopic expression in the susceptible apple rootstock M.26. Stable EFR expression led to the activation of PAMP-triggered immune response in apple leaves upon treatment with supernatant of E. amylovora, as measured by the production of reactive oxygen species and the induction of known defense genes. The amount of tissue necrosis associated with E. amylovora infection was significantly reduced in the EFR transgenic rootstock compared to the wild-type. Our results show that the expression of EFR in apple rootstock may be a valuable biotechnology strategy to improve the resistance of apple to fire blight.

Tackling multiple bacterial diseases of Solanaceae with a handful of immune receptors

“…This first breakthrough was followed by numerous studies based on the transfer of PRRs between plant species. Thus, EFR can confer resistance to P. syringae, R. solanacearum and/or Xanthomonas species in tomato, potato, rice, wheat, Medicago, and sweet orange and could even protect apple rootstock from the fire blight caused by E. amylovora (Lacombe et al 2010;Lu et al 2015;Schoonbeek et al 2015;Schwessinger et al 2015;Boschi et al 2017;Pfeilmeier et al 2019;Mitre et al 2021;Piazza et al 2021). Of note, the constitutive expression of EFR in the transgenic plants did not alter growth nor the associated microbiome and did not cause yield penalties (Pfeilmeier et al 2019;Piazza et al 2021).…”

“…Thus, EFR can confer resistance to P. syringae, R. solanacearum and/or Xanthomonas species in tomato, potato, rice, wheat, Medicago, and sweet orange and could even protect apple rootstock from the fire blight caused by E. amylovora (Lacombe et al 2010;Lu et al 2015;Schoonbeek et al 2015;Schwessinger et al 2015;Boschi et al 2017;Pfeilmeier et al 2019;Mitre et al 2021;Piazza et al 2021). Of note, the constitutive expression of EFR in the transgenic plants did not alter growth nor the associated microbiome and did not cause yield penalties (Pfeilmeier et al 2019;Piazza et al 2021). Moreover, EFR has also been successfully deployed together with the pepper NLR BACTERIAL SPOT RESIST-ANCE 2 (Bs2) in transgenic tomato for the concomitant field management of bacterial wilt and bacterial spot, highlighting the advantages of stacking different types of immune receptors to achieve durable resistance in crops (Kunwar et al 2018).…”

Root Breeding in the Post-Genomics Era: From Concept to Practice in Apple

“…Elongation factor thermal unstable (EF-Tu) is one of the most abundant bacterial proteins and functions as a very potent PAMP in Arabidopsis thaliana . The ectopic expression of Arabidopsis EF-Tu in apple rootstock M.26 significantly enhanced its resistance to the bacterium Erwinia amylovora [ 52 ]. Recognition and immune regulation during the plant response to biotic stress have been extensively studied, but the hypotheses that have been proposed in recent years must be further verified in apple.…”

Overexpression of Lectin Receptor-Like Kinase 1 in Tomato Confers Resistance to Fusarium oxysporum f. sp. Radicis-Lycopersici

“…Both RLKs and RLPs contain an extracellular domain that perceives extracellular signals; RLKs transduce these signals via their intracellular kinase domain to trigger defense-related gene expression and the synthesis of defensive chemicals, including plant hormones, reactive oxygen species, and callose to enhance plant disease resistance (Park et al, 2012;Tang et al, 2017). The roles of RLKs in response to pathogenic bacteria have been extensively studied in many plant species, and some RLKs are considered ideal candidates for molecular breeding programs (Robatzek et al, 2006;Schwessinger et al, 2015;Pizarro et al, 2018;Piazza et al, 2021). However, little is known about whether and which RLKs are involved in tomato resistance to FORL.…”