Wheat tandem kinases provide insights on disease‐resistance gene flow and host–parasite co‐evolution

Abstract

Summary Stripe (yellow) rust, caused by the fungus Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat spread globally. Wild emmer wheat (Triticum turgidum ssp. dicoccoides; WEW) is known as a source for novel Pst resistance genes (R‐gene), but our knowledge on wheat‐Pst co‐evolution in natural populations is limited. Yr15 is a WEW (accession G25) gene, which confers a broad‐spectrum resistance to Pst, and encodes a tandem kinase‐pseudokinase protein designated as WTK1. Exon–intron comparisons of multiple WTK1 homoeologous and paralogous copies scattered in allopolyploid wheat genomes enabled us to develop functional molecular markers (FMMs), which were used for population genetic study. The functional allele (Wtk1) was absent in a worldwide collection of 513 wheat cultivars, except for 32 introgression lines with Yr15 from G25, as well as in 84% of the 382 tested WEW accessions collected across the Fertile Crescent. Yr15 was found to be distributed along a narrow axis from Mt Carmel to the Anti‐Lebanon Mountains ridge, mostly at elevations above c. 500 m, where the climatic conditions are favorable for disease development, therefore providing insights on gene flow and host–parasite co‐evolution in WEW natural habitats. Moreover, the worldwide absence of Wtk1 in cultivated wheat and in WEW natural populations from southeast Turkey, where wheat is believed to have been domesticated, proposes that Yr15 was rather left behind, than lost during domestication. Our results highlight the importance of conservation of WEW populations in their natural habitats for discovery of novel R‐genes and studies of host–parasite co‐evolution.

Three previously characterized resistances to yellow rust are encoded by a single locusWtk1

“…Functional markers detected alternate alleles in WEW, T. turgidum ssp. durum , and T. aestivum that were consistent with the phenotypic responses (Klymiuk et al , 2019b).…”

“…Yellow rust test was carried out with Pst isolate #5006 (race 38E134) using a standard protocol for Pst inoculation described in Klymiuk et al (2019b). Ten plants per genotype were inoculated at seedling stage (the two-leaf stage).…”

“…Detailed descriptions of the development, sequences and conditions for amplification of KASP Yr15 functional molecular markers are provided in Klymiuk et al (2019b). Names, primer sequences, and references of other previously published markers are presented in Table S1 .…”

“…Full-length sequences of Wtk1 from G25, G303 and H52 were previously published (Klymiuk et al , 2018; Klymiuk et al , 2019b) and have been deposited in NCBI GenBank under accession numbers MG649384, MK188918 and MK188919, respectively. An alignment of WTK1 KinI and KinII domains was performed with ClustalW software (Thompson et al , 1994).…”

“…WEW is the undomesticated polyploid progenitor for modern cultivated tetraploid durum wheat (BBAA) and hexaploid common wheat (BBAADD) and natural populations still grow in a wide range of ecogeographical conditions distributed across the Near East Fertile Crescent (Özkan et al , 2011). These natural populations can serve as a model to study the evolutionary processes that shaped the currently observed allelic variation (Yahiaoui et al , 2009; Sela et al , 2011; Huang et al , 2016b; Lundström et al , 2017; Klymiuk et al , 2019b). Several previous studies have reported that WEW accessions exhibit high levels of resistance to inoculation with Pst isolates (Gerechter-Amitai and Stubbs, 1970; Van Silfhout, 1989; Nevo et al , 1986).…”