Effector-mediated discovery of a novel resistance gene against Bremia lactucae in a nonhost lettuce species

• Published in: The New phytologist Vol. 216; no. 3; pp. 915 - 926
• Main Authors: Giesbers, Anne K. J., Pelgrom, Alexandra J. E., Visser, Richard G. F., Niks, Rients E., Van den Ackerveken, Guido, Jeuken, Marieke J. W.
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01.11.2017; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: Airborne microorganisms; Amino Acid Motifs; avirulence; Breeding; Bremia; Disease resistance; Disease Resistance - genetics; Downy mildew; Effectors; effector‐triggered immunity (ETI); EPS; Exploitation; Fungal Proteins - genetics; Fungal Proteins - metabolism; Fungi; Gene expression; Genes; Germplasm; Heredity; Hypersensitive response; Laboratorium voor Plantenveredeling; Laboratory of Plant Breeding; Lactuca - genetics; Lactuca - microbiology; Lactuca saligna; Lettuce; lettuce downy mildew; nonhost resistance; oomycete; Oomycetes - genetics; Oomycetes - pathogenicity; Pathogens; PBR Non host and insect resistance; PBR Non host en Insectenresistentie; PE&RC; Plant Breeding; Plant Diseases - genetics; Plant Diseases - microbiology; Plant Proteins - genetics; Quantitative Trait Loci; quantitative trait locus (QTL); R gene; Segregation; Species; lettuce downy mildew; Lactuca saligna; oomycete; R gene; avirulence; quantitative trait locus (QTL); nonhost resistance; effector-triggered immunity (ETI)
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.14741

Candidate effectors from lettuce downy mildew (Bremia lactucae) enable high-throughput germplasm screening for the presence of resistance (R) genes. The nonhost species Lactuca saligna comprises a source of B. lactucae R genes that has hardly been exploited in lettuce breeding. Its cross-compatibility with the host species L. sativa enables the study of inheritance of nonhost resistance (NHR). We performed transient expression of candidate RXLR effector genes from B. lactucae in a diverse Lactuca germplasm set. Responses to two candidate effectors (BLR31 and BLN08) were genetically mapped and tested for co-segregation with disease resistance. BLN08 induced a hypersensitive response (HR) in 55% of the L. saligna accessions, but responsiveness did not co-segregate with resistance to Bl:24. BLR31 triggered an HR in 5% of the L. saligna accessions, and revealed a novel R gene providing complete B. lactucae race Bl:24 resistance. Resistant hybrid plants that were BLR31 nonresponsive indicated other unlinked R genes and/or nonhost QTLs. We have identified a candidate avirulence effector of B. lactucae (BLR31) and its cognate R gene in L. saligna. Concurrently, our results suggest that R genes are not required for NHR of L. saligna.