The Arabidopsis immune receptor EFR increases resistance to the bacterial pathogens Xanthomonas and Xylella in transgenic sweet orange

Abstract

SummaryPlants employ cell surface receptors to recognize pathogen (or microbe)-associated molecular patterns (PAMPs/MAMPs), which are crucial for immune system activation. The well-studied Arabidopsis thaliana ELONGATION FACTOR-TU RECEPTOR (EFR) recognizes the conserved bacterial PAMP EF-Tu, and the derived peptides elf18 and elf26. The interfamily transfer of EFR has been shown to increase disease resistance in several crops, such as tomato, rice, wheat, and potato. Here, we generated sweet orange (Citrus sinensis) transgenic lines expressing EFR to test if it would confer broad-spectrum resistance against two important citrus bacterial diseases: citrus canker and citrus variegated chlorosis (CVC). Independent EFR transgenic lines gained responsiveness to elf18 and elf26 peptides from Xanthomonas citri and Xylella fastidiosa, as measured by reactive oxygen species (ROS) production, mitogen-activated protein kinase (MAPK) activation and defense gene expression. Consistently, infection assays showed that Citrus-EFR transgenic plants were more resistant to citrus canker and CVC. Our results show that the EFR immune receptor can improve plant immunity in a perennial crop against bacterial pathogens, opening perspectives to engineer durable broad-spectrum disease resistance under field conditions.

Expression of putative effectors of different Xylella fastidiosa subspecies/strains reveals recognition and defense activation in various model plants

“…In summary, our findings, open possibilities and encourage further investigation and identification of the related PRRs that could be a potential biotechnological tool to confer broad-spectrum disease resistance against X. fastidiosa . Quite recently, the expression of a PRR receptor in sweet orange has been shown to confer ligand-dependent activation of defense responses against a citrus infecting strain of X. fastidiosa (Mitre et al, 2021).…”

Xylella fastidiosa’s relationships: the bacterium, the host plants, and the plant microbiome

“…The immunogenic activity of subspecies fastidiosa and pauca was demonstrated using whole cell samples, purified LPS, and corresponding elf18/26 peptides. Their application to Arabidopsis, citrus, and grapevine provoked prototypic immune responses of PRR signalling, including a transient production (burst) of reactive oxygen species (ROS), phosphorylation of mitogen‐activated protein kinases, and repression of seedling growth (Rapicavoli et al ., 2018; Mitre et al ., 2021). A recent study identified the first PRR involved in the recognition of X. fastidiosa .…”

“…A recent study identified the first PRR involved in the recognition of X. fastidiosa . The well‐characterized EF‐Tu Receptor (EFR) and BRI1‐Associated Kinase 1 PRR/co‐receptor pair for EF‐Tu confers immune signalling to X. fastidiosa elf18/26 peptides and controls X. fastidiosa infection success (Mitre et al ., 2021). Being only present in Brassicaceae plants, genetic transfer of EFR into citrus gained immune responsiveness and limited CVC systemic symptoms, suggesting that PRR‐activated immune signalling plays an important role in controlling systemic spread of X. fastidiosa .…”

Expression of putative effectors of different Xylella fastidiosa strains triggers cell death‐like responses in various Nicotiana model plants

“…In summary, our findings open up new research possibilities and encourage further investigation and identification of the related PRRs that could be a potential biotechnological tool to confer broad-spectrum disease resistance against Xf. Quite recently, the expression of a PRR receptor in sweet orange was reported to confer ligand-dependent activation of defence responses against a citrus-infecting strain of Xf (Mitre et al, 2021).…”

“…Successful vascular wilt pathogens achieve spread throughout xylem vessels by degrading cell walls and pit membranes and invading parenchyma cells while resistant hosts detect MAMPs, DAMPs, or secreted virulence factors and prevent systemic spread (Choi & Klessig, 2016). It is noteworthy that an already well-characterized immune receptor (PRR) from the model plant Arabidopsis thaliana, known as ELONGATION FACTOR-TU RECEPTOR (EFR), which recognizes the conserved bacterial PAMP EF-Tu and derived elf peptides, was recently shown to confer increased resistance against Xf when expressed in sweet orange, a conditionally susceptible host of this microbe (Mitre et al, 2021).…”