Continuation of Collaborative Phytophthora Root Rot Genetic Resistance Studies

Grants and Contracts Details


Title: • Validation of the candidate genes associated with susceptibility and resistance to P. cinnamomi in American and Chinese chestnut • Ellen Crocker, Department of Forestry and Natural Resources, University of Kentucky Sponsor: Jared Westbrook, The American Chestnut Foundation (TACF) PI: Success in restoring the American chestnut to its native range relies on introducing resistance to both major pathogens, Cryphonectria parasitica (Cp) and Phytophthora cinnamomi (Pc), causing chestnut blight and Phytophthora root rot (PRR), respectively. In the southeastern US, where PRR kills chestnut trees by the roots before chestnut blight even has the chance to act, resistance to Pc is critical for restoration efforts. To support the resistance breeding, we conducted the QTL analysis in American chestnut × Chinese chestnut crosses derived from ‘Mahogany’ and ‘Nanking’, two sources of resistance to Pc in the TACF breeding program (Zhebentyayeva et al., 2019). The QTL intervals were delineated, first, on pseudochromosomes of the Chinese chestnut (Vanuxem) genome assembly (Staton et al., 2000). Second (and currently), the genic content of QTLs underlying the Pc resistance was recently established in high-quality Chinese chestnut genomes of Mahogany and Nanking trees. Gene expression profiling during the early response to Pc zoospores at 3, 6, 12 and 24 hours after inoculation (hai) revealed differences in the timing of molecular responses in American and Chinese chestnut roots. In resistant Chinese chestnut, activation of gene families involved in plant immunity occurred at 12 hai, while in susceptible American chestnut these gene families activated at 24 hai. On the pathogen side, effectors elicited by the pathogen in susceptible and resistant chestnut roots were identified and used for sketching key elements of the pathogen-host interaction in the P. cinnamomi-Castanea pathosystem. Based on prior genetic information (positioning within QTL intervals for Pc resistance and genome-wide neutrality tests) and our recent differential gene expression results, four genes were selected for further characterization as candidate genes for Pc resistance in Chinese chestnut. These are: membrane-anchored receptor-like protein kinases CmMahoganyH1.05G141800 and CmMahoganyH1.05G141900, tetrahydroberberine oxidase (CmMahoganyH1.05G146400) and ethylene-forming aminocyclopropanecarboxylate oxidase (CmMahoganyH1.05G169800). In American chestnut, two candidate genes for susceptibility to Pc were identified-- a putative JA- signaling repressor TIFY 5A-related protein (Caden.05G176200) and a highly activated HXXXD-type acyltransferase (Caden.05G298000). Essential to candidate gene validation is independent verification of the previously noted differences in transcriptomics profiles. Here we propose validating these candidate genes in an independent Pc-treatment experiment using RT-qPCR which is considered the gold-standard method for quantifying RNA transcript abundance changes within an organism. Subsequently, validated candidate resistance and susceptibility genes can be targeted for functional characterization in transgenic American chestnut. Also, candidate gene-targeted markers could supplement a set of markers for screening the TACF breeding material for resistance to Pc and Cp.
Effective start/end date4/1/249/30/24


  • American Chestnut Foundation: $27,682.00


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