A lineage-specific Exo70 is required for receptor kinase–mediated immunity in barley

Abstract

In the evolution of land plants, the plant immune system has experienced expansion in immune receptor and signaling pathways. Lineage-specific expansions have been observed in diverse gene families that are potentially involved in immunity but lack causal association. Here, we show that Rps8 -mediated resistance in barley to the pathogen Puccinia striiformis f. sp. tritici (wheat stripe rust) is conferred by a genetic module: Pur1 and Exo70FX12 , which are together necessary and sufficient. Pur1 encodes a leucine-rich repeat receptor kinase and is the ortholog of rice Xa21 , and Exo70FX12 belongs to the Poales-specific Exo70FX clade. The Exo70FX clade emerged after the divergence of the Bromeliaceae and Poaceae and comprises from 2 to 75 members in sequenced grasses. These results demonstrate the requirement of a lineage-specific Exo70FX12 in Pur1-mediated immunity and suggest that the Exo70FX clade may have evolved a specialized role in receptor kinase signaling.