Divergent molecular pathways govern temperature-dependent wheat stem rust resistance genes Sr6, Sr13 and Sr21

Abstract

The wheat stem rust pathogen, Puccinia graminis f. sp. tritici (Pgt), has caused devastating crop losses worldwide. Several stem rust resistance (Sr) genes display temperature-dependent immune responses. Sr6-mediated resistance is enhanced at lower temperatures whereas Sr13 and Sr21 resistances are enhanced at higher temperatures. Here we report cloning of Sr6 by mutagenesis and resistance gene enrichment and sequencing (MutRenSeq), showing it to encode an NLR protein with an integrated BED domain. Sr6 temperature sensitivity was also transferred to wheat plants transformed with the Sr6 transgene. Differential gene expression analysis using near-isogenic wheat lines inoculated with Pgt at varying temperatures revealed that genes upregulated in the low-temperature-effective Sr6 response differed significantly from those upregulated in the high-temperature-effective responses associated with Sr13 and Sr21. Understanding the molecular mechanisms and pathways involved in temperature sensitivity can inform future strategies for deployment and engineering of genetic resistance in response to a changing climate.