Pioneering “non-host” genetic resistance against Asian soybean rust by molecular mapping of a novel QTL in Medicago truncatula

Robinson, Kelly (2024) Pioneering “non-host” genetic resistance against Asian soybean rust by molecular mapping of a novel QTL in Medicago truncatula. Doctoral thesis, University of East Anglia.

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Abstract

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is a major disease impacting global soybean production, particularly due to limited genetic resistance in soybean. Non-host resistance (NHR) is proposed to be a durable, broad-spectrum form of resistance. While the model legume Medicago truncatula is described as a “non-host” of P. pachyrhizi, lack of susceptible accessions has inhibited genetic studies to map resistance. In this thesis I explored M. truncatula as a source of genetic resistance to P. pachyrhizi and used this system to characterise pathogen-secreted molecules, effectors, which are key determinants of infection. By screening 37 M. truncatula accessions with a highly virulent Brazilian isolate, UFV02, we report for the first time differential immune, resistant, and sporulating susceptible phenotypes. A bi-parental F2 mapping population (Mt_19 (S) x Mt_34 (R)) segregated 3:1 for resistance. Using 4,678 GBS-based SNPs, I constructed a high-density physical map with a total length of 391.64 Mb. By performing QTL mapping, I identified a single major QTL (MtRpp1) spanning 7.3 Mb with peak LOD of 31.7 that explained 58.27% phenotypic variance. Fine-mapping narrowed the interval to a 759 kb region containing 33 candidate genes. Of these, an ABCG32 transporter and a metacaspase7-like gene were prioritised. I performed Markov cluster (MCL) analysis with the UFV02 de novo transcriptome and 9 rust fungal secretomes to identify an expanded family of effectors, Tribe_36. This tribe contained 8 P. pachyrhizi effectors, including the published effector PpEC23 (2BE_260) that interacts with the soybean GmSPL12l. To identify effector host targets in M. truncatula, 2BE_460 and a novel homologue, 2BE_047, were screened against a yeast-two-hybrid cDNA library. In planta validation of their interaction with host proteins revealed these effectors display non-specific binding. This work establishes the genetic basis of resistance to ASR in M. truncatula and explores the molecular basis of NHR.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	27 Mar 2025 09:48
Last Modified:	27 Mar 2025 09:48
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98889
DOI:

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