Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

Abstract

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive foliar diseases of wheat. In this study, we combined the bulked segregant RNA sequencing (BSR-seq) and comparative genomics analysis to localize the powdery mildew resistance gene in Chinese landrace Xiaomaomai. Genetic analysis of F1 plants from a crossing of Xiaomaomai × Lumai23 and the derived F2 population suggests that a single recessive gene, designated as pmXMM, confers the resistance in this germplasm. A genetic linkage map was constructed using the newly developed SNP markers and pmXMM was mapped to the distal end of chromosome 2AL. The two flanking markers 2AL15 and 2AL34 were closely linked to pmXMM at the genetic distance of 3.9 cM and 1.4 cM, respectively. Using the diagnostic primers of Pm4, we confirmed that Xiaomaomai carries a Pm4 allele and the gene function was further validated by the virus-induced gene silencing (VIGS). In addition, we systematically analyzed pmXMM in comparison with the other Pm4 alleles. The results suggest that pmXMM is identical to Pm4d and Pm4e at sequence level. Pm4b is also not different from Pm4c according to their genome/amino acid sequences. Only a few nucleotide variances were detected between pmXMM and Pm4a/b, which indicate the haplotype variation of the Pm4 gene.

The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast

“…An allelic series of Pm4 , each recognizing different isolates of Bgt , has been reported, and many of these originate from wild relatives of T. aestivum 20 . Pm4b / Pm4c share 100% nucleotide sequence identity, as do Pm4d / Pm4e , and are henceforth referred to as Pm4b and Pm4d , respectively 24 . Pm4a and Pm4b were introduced from tetraploid wheats 25 , 26 , while Pm4d is believed to have been introgressed from Triticum monococcum 27 .…”

PmSN15218: A Potential New Powdery Mildew Resistance Gene on Wheat Chromosome 2AL

“…We also performed de novo assembly using DNA resequencing data of SN15218 and found no Pm4b-Fed gene or fragment in the assembly database. In addition, we compared five other Pm genes, PmX ( Fu et al, 2013 ), PmLK906 ( Niu et al, 2008 ), PmPS5A ( Niu et al, 2010 ), PmMl92145E8-9 ( Yu et al, 2018 ), and PmXMM ( Yao et al, 2022 ), which were also located on chromosome 2AL ( Supplementary Table 1 ). Three of these, PmX , PmLK906 , and PmPS5A , shared similar physical locations with Pm SN15218 , but PmMl92145E8-9 and PmXMM were located in the proximal region of the Pm4 locus.…”

“…Since the two genes have different donors, the contradictory localization results could be due to ectopic recombination that occurred during transfer to the common wheat background. To determine the allelic relationship of Pm SN 15218 and Pm4b-Fed , we tested JS717 × JS718 and Pm4.1 , two specific markers for Pm4b-Fed ( Sánchez-Martín et al, 2021 ; Yao et al, 2022 ), and a newly developed marker, Pm4b-Fed-S ( Supplementary Table 1 ), and found that this gene was not present in HXH, YN19, or SN15218. In addition, we analyzed the closely linked markers of other Pm genes, including PmX , Pm65 , PmLK906 , PmPS5A , and PmMl92145E8-9 , on chromosome 2AL using in silico PCR ( Supplementary Table 2 ).…”

Harnessing Knowledge from Plant Functional Genomics and Multi-Omics for Genetic Improvement

“…In wheat, Feng et al reported a new disomic substitution line containing the Leymus mollis ( L. mollis ) 2N chromosomal fragments and, more importantly, identified 13 markers by SLAF-seq for tracing the chromosome 2Ns of L. mollis in the wheat line [ 32 ]. Another study combined bulked segregant RNA sequencing (BSR-seq), comparative genomics and linkage mapping to map a recessive powdery mildew resistance gene pmXMM to the distal end of chromosome 2AL [ 33 ]. In maize, Guan et al mapped four QTLs (qTBN2a, qTBN2b, qTBN4, qTBN6) of the tassel branch number (TBN) trait and identified six candidate genes within the QTL regions.…”