<p>Phytophthora
root and stem rot (PRSR), caused by oomycete <i>Phytophthora sojae</i>, is the
most severe soil-borne disease of soybean (<i>Glycine max</i> (L.) Merr.) worldwide.
The disease can be effectively managed by introducing resistance to <i>P. sojae</i>
(<i>Rps</i>) genes into soybean cultivars by breeding, which requires
continuous efforts on identification of resistance resources from soybean
germplasm. Previously, two resistance genes, <i>Rps2-cas</i> (former name <i>Rps2-das</i>)
and <i>Rps14 </i>(former name<i> Rps1-f</i>), were mapped by linkage analysis
from soybean landraces, PI 594549 C and PI 340029, respectively. The resistance
underlying PI 594592 also need further characterization given its broad
resistance spectrum. In this study, <i>Rps-2cas</i> and <i>Rps14</i> were
further mapped, and <i>Rps2-b</i>, was identified and initial mapped from PI
594592. Thus, this thesis research was divided into three parts for three <i>Rps</i>
genes.</p><p>The first part
mainly focuses advances on <i>Rps2-cas</i>. Marker-assisted spectrum analysis
was performed for <i>Rps-2cas</i> to confirm its potential in disease
management. A high-quality genome assembly of PI 594549 C was generated, and
KASP markers were developed based on comparison between new reference and
Williams 82 reference genome. The gene was further mapped to a 32.67-kb region
on PI 594549 C reference genome harboring three expressed NLRs by 24
recombinants screened from a large F<sub>4</sub> population. Comparative
genomics analysis suggests the only intact NBS-LRR gene in the fine mapping
region is the best candidate gene for <i>Rps2cas</i>, and its function was
validated by stable transformation. Evidences from other high-quality assembly
genomes suggest <i>Rps2-cas</i> originated from an ancient unequal crossing
over event.</p>
<p>In the second
part, <i>Rps14</i> was further mapped using 21 recombinants identified from a F<sub>3
</sub>population consisting of 473 plants. In commonly used Williams 82
reference genome, the assembly of fine mapping region was incomplete, and <i>Rps14</i>
region showed drastic variation in size and copy number of NLRs in 23
high-quality genome assemblies, suggesting the complexity of <i>Rps14</i>
region and high-quality reference sequence of donor line is required for
isolation of <i>Rps14</i> candidate genes. Marker assisted resistance test
showed <i>Rps14</i> had wider resistance spectrum to different <i>P. sojae </i>isolates
comparing to other <i>Rps</i> genes on chromosome 3, and phylogenic analysis
further supported the potential of <i>Rps14</i> to be a novel resistance gene. </p>
<p>For the third
part, an F<sub>2 </sub>population derived from a cross between PI 594592 and
Williams was tested by <i>P. sojae</i> race 1. The 3:1 and 1:2:1 Mendelian
segregation ratios were observed in F<sub>2 </sub>individuals and F<sub>2:3 </sub>families,
respectively, suggesting a single dominant <i>Rps</i> gene in PI 594592. The
gene was initially mapped to the distal end chromosome 16 overlapped with <i>Rps2</i>,
and the gene was tentatively named as <i>Rps2-b</i>. Polymorphic SSR markers
and InDel markers designed based on re-sequencing data of PI 594592 and
Williams was used to genotyping all the F<sub>2:3 </sub>families, and a linkage
map was constructed for <i>Rps2-b</i>. <i>Rps2-b</i> was mapped to a 461.8-kb
region flanked by SSR marker Satt431 and InDel marker InDel3668 according to the
reference genome (Wm82. a2). Marker-assisted resistance test showed <i>Rps2-b</i>
hold a wide resistance spectrum. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/15074508 |
| Date | 29 July 2021 |
| Creators | Liyang Chen (8744436) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Molecular_identification_of_Phytophthora_resistant_genes_in_soybean/15074508 |
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