Phytophthora sojae infection severely impairs soybean production. We previously identified a dirigent protein, GmDRR1 (Glycine max Disease Resistant Response 1), that increases soybean resistance to P. sojae. However, the molecular basis of GmDRR1 function remained largely uncharacterized. In the present study, analysis of GmDRR1-RNAi, GmDRR1-overexpressing, and CRISPR/Cas9-derived Gmdrr1 mutant lines revealed that GmDRR1 expression significantly restricted P. sojae growth. Combining co-immunoprecipitation with liquid chromatography–tandem mass spectrometry revealed a GmDRR1-interacting protein, GmDRR2, which is homologous to GmDRR1. An E-coniferyl alcohol coupling assay indicated that GmDRR1 promotes the synthesis of (+)-pinoresinol, which helps to protect plants from P. sojae. The GmNAC1 (Glyma.05G025500) transcription factor bound to the GmDRR1 promoter both in vitro and in vivo to upregulate GmDRR1 expression. Soybean resistance to P. sojae was increased by overexpression of GmNAC1. Our findings suggest a novel signaling pathway involving a NAC transcription factor that mediates soybean resistance to P. sojae. Specifically, GmNAC1 directly induces GmDRR1 expression to increase resistance of soybean plants to P. sojae.

Powdery mildew, caused by Erysiphe pisi D.C., is an important disease of pea (Pisum sativum L.). The use of cultivars carrying powdery mildew resistance alleles at the er1 locus is the most effective and economical means of controlling this disease. The objectives of this study were to screen Chinese elite pea cultivars for resistance to E. pisi and to identify the responsible gene at the er1 locus. Among the 37 pea cultivars tested, three (Yunwan 8, Yunwan 21, and Yunwan 23) were immune to E. pisi infection in phenotypic evaluations. The full-length cDNA sequences of the er1 candidate gene, PsMLO1, from the three resistant cultivars and control plants were analyzed. Comparison of the cDNA sequences of 10 clones revealed differences among the powdery mildew-resistant cultivars, susceptible controls, and wild-type cultivar Sprinter. The observed resistance in Yunwan 8 plants resulted from a point mutation (C→G) at position 680 of PsMLO1 that introduced a stop codon, leading to premature termination of protein synthesis. The responsible resistance allele was identified as er1–1. Powdery mildew resistance in Yunwan 21 and Yunwan 23 plants was caused by identical insertions or deletions in PsMLO1. Three distinct PsMLO1 transcripts were observed in Yunwan 21 and Yunwan 23 plants. These transcripts were characterized by a 129-bp deletion and 155- and 220-bp insertions, respectively. The responsible resistance allele was identified as er1–2. We have characterized two important er1 alleles in three E. pisi-resistant pea cultivars bred in Yunnan Province, China. These cultivars represent important genetic resources for the breeding of powdery mildew-resistant pea cultivars.

Powdery mildew, caused by Erysiphe pisi D.C., is a major constraint to pea production worldwide. The pea cultivar Xucai 1 has shown high resistance to E. pisi under greenhouse and field conditions. The objectives of this study were to identify and characterize genes conferring resistance to powdery mildew in Xucai 1. Three crosses, Qizhen 76 × Xucai 1, Bawan 6 × Xucai 1, and Xucai 1 × Bawan 6, were made to generate populations for genetic analysis. The resistance to E. pisi and segregation ratios in the F₁, F₂, and F_2:3 populations suggested a single recessive gene conferring the resistance of Xucai 1. Bulked segregant analysis was used to map the resistance gene using two F₂ populations. The resistance gene was close to markers AD60 and c5DNAmet on linkage group VI with genetic distances of 9.9 cM and 15.4 cM in the Xucai 1 × Bawan 6 F₂ population and 8.7 cM and 8.1 cM in the Qizhen 76 × Xucai 1 F₂ population, respectively, suggesting that the resistance gene was an er1 allele. This hypothesis was confirmed by comparison of the cDNA sequences of the PsMLO1 gene between the parents and the PsMLO1 wild type. Three distinct types of transcripts in Xucai 1, characterized by a 129-bp deletion and 155- and 220-bp insertions, were detected, consistent with the structure of the er1-2 allele. We concluded that resistance in Xucai 1 was conferred by er1-2 and that its linked markers will be useful in pea breeding programs.