Candidate Genes for Fungal Resistance: Mapping and SNP Development for LysM-Domain Encoding Genes in Soybean.

Chitin is a normal component of fungal cell walls and is also known to induce a plant defense response similar to that seen upon fungal pathogen infection.  The Stacey lab has demonstrated that members of the LysM-receptor kinase (LysM-RLK) family likely serve as the receptor for chitin.  A mutation in LysM-RLK3 resulted in a constitutive chitin response and elevated response to fungal pathogen infection, suggesting that the wild-type receptor acts to repress a chitin response, which would then be de-repressed upon chitin recognition.  This information suggests that the LysM genes represent promising candidate genes that could explain some of the resistance to white mold in selected genotypes.  Analyses of soybean sequence databases indicated that soybean has 13 unique LysM-RLKs and at least another 17 LysM-domain containing proteins.  The genes were cloned and sequenced.  The objectives of this study are to (1) map LysM-domain encoding genes in soybean and correlate their map locations to known white mold QTLs, and (2) develop SNP markers for those LysM-domain genes mapping close to known white mold QTLs.  Five soybean RIL populations used previously to identify QTLs for sclerotinia resistance will be used in this analysis.  The common susceptible parent is the cultivar Williams 82.  Out of 42 LysM-domain genes considered, we identified 37 that were located on Linkage Groups that contained significant QTL from our previous work.  To date, we have determined that six of the LysM genes map to locations where we identified QTL on LGs D1b, E, F, G, K, and L.  LysM genes on LG A1, B1, and D1a were not associated with our identified QTLs.  We are in the process of identifying SNPs for the LysM genes in Williams 82 and the five susceptible parents of the RIL populations, and we will map selected LysM genes in those 5 populations.  The SNP markers that are developed could be used for marker-assisted breeding to develop near-isogenic lines and potentially cultivars with improved resistance.