|MASSONNET, MELANIE - University Of California, Davis|
|VONDRAS, AMANDA - University Of California, Davis|
|COCHETEL, NOE - University Of California, Davis|
|PAP, DANIEL - University Of California, Davis|
|MINIO, ANDREA - University Of California, Davis|
|FIGUEROA BALDERAS, ROSA - University Of California, Davis|
|WALKER, ANDREW - University Of California, Davis|
|CANTU, DARIO - University Of California, Davis|
Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2022
Publication Date: 6/13/2022
Citation: Massonnet, M., Vondras, A.M., Cochetel, N., Riaz, S., Pap, D., Minio, A., Figueroa Balderas, R., Walker, A.M., Cantu, D. 2022. Haplotype-resolved powdery mildew resistance loci reveal the impact of heterozygous structural variation on NLR genes in Muscadinia rotundifolia. Horticulture Research. 12(8). https://doi.org/10.1093/g3journal/jkac148.
Interpretive Summary: The grape genus Muscadinia rotundifolia is a reservior of disease resistance genes to multuple diseases; resistance to fungal disease powdery mildew is one of them. In this study, two gentic loci Run1.2 and Run2.2 from cultivar Trayshed were characterized. For both loci, nucleotide-binding leucine-rich repeat (NLR) genes is predominant class, and the number, classes of NLR genes and their expression vary between loci as well as haplotype of each locus.
Technical Abstract: Muscadinia rotundifolia cv. Trayshed is a valuable source of resistance to grape powdery mildew (PM). It carries two PM resistance (R) loci, Run1.2 on chromosome 12 and Run2.2 on chromosome 18. This study identified the nucleotide-binding leucine-rich repeat (NLR) genes composing each R locus and their associated defense mechanisms. Evaluation of PM disease development showed that introgression of both loci confers resistance to PM in a V. vinifera background, but with varying speed and intensity of the response. To better understand the effect of NLR composition on PM resistance, both haplotypes of each R locus were reconstructed and the gene models within each haplotype were manually refined. We found that the number and classes of NLR genes differed between Run1.2 and Run2.2 loci and between the haplotypes of each R locus. In addition, NLR genes composing Run1.2b or Run2.2 loci exhibited different levels of gene expression, pointing to candidate NLR genes responsible for PM resistance in Trayshed. Finally, transcriptomic analysis showed differences in the defense mechanisms associated with Run1.2b and Run2.2 in response to PM and at constitutive level. Altogether, our results reveal that Trayshed’s R loci are composed of distinct NLRs that trigger different plant defense mechanisms in response to PM and at constitutive level, which would explain the variation of pathogen restriction between the two loci.