A five-transgene cassette confers broad-spectrum resistance to a fungal rust pathogen in wheat
Résumé
Breeding wheat with durable resistance to the fungal pathogen Puccinia graminis f. sp. tritici (Pgt), a major threat to cereal production, is challenging due to the rapid evolution of pathogen virulence. Increased durability and broad-spectrum resistance can be achieved by introducing more than one resistance gene, but combining numerous unlinked genes by breeding is laborious. Here we generate polygenic Pgt resistance by introducing a transgene cassette of five resistance genes into bread wheat as a single locus and show that at least four of the five genes are functional. These wheat lines are resistant to aggressive and highly virulent Pgt isolates from around the world and show very high levels of resistance in the field. The simple monogenic inheritance of this multigene locus greatly simplifies its use in breeding. However, a new Pgt isolate with virulence to several genes at this locus suggests gene stacks will need strategic deployment to maintain their effectiveness. Pgt continues to overcome resistant wheat cultivars, with three new, highly virulent isolates emerging in the last 20 years, and the disease reappearing in Europe and the UK 1. Two classes of Pgt resistance genes have been cloned from wheat: all-stage resistance (ASR) genes and adult plant resistance (APR) genes 2. ASR genes (for example, Sr22 (ref. 3), Sr35 (ref. 4), Sr45 (ref. 3) and Sr50 (ref. 5)) generally encode nucleotide-binding, leucine-rich repeat (NLR) proteins that recognize a specific Pgt molecule (an effector) introduced into host plant cells by the fungus to promote parasitism, whereupon a plant defense response is activated 2. The presence, absence or allelic variation of the fungal effector determines which Pgt isolates an ASR gene is effective against. ASR genes are extremely valuable for crop protection but, when deployed singly, often show transient resistance, as pathogen effectors rapidly evolve to avoid recognition. Combining ASR genes increases their durability, and theoretical estimates suggest that the chance of a single Pgt isolate gaining virulence for five or more ASR genes in wheat is infinitesimally small 6. The second gene class, APR genes, can be remarkably durable and, in some cases, effective against multiple pathogen species. However, these genes generally provide partial resistance that is often insufficient for crop protection during severe pathogen epidemics.
Domaines
Sciences du Vivant [q-bio]
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Licence : CC BY - Paternité
