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

Plants 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.