|Zheng, Ping - Washington State University Extension Service|
|Main, Dorrie - Washington State University Extension Service|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2014
Publication Date: N/A
Technical Abstract: The defense response of apple rootstocks to necrotrophic soilborne pathogens that incite apple replant disease (ARD) has not been investigated. In this study, apple root tissues inoculated with Pythium ultimum, including those for mock inoculation, were sampled at 0, 1, 4, 8, 24, 48, 72 and 96 hour post inoculation (hpi). RNA-Seq based transcriptome profiling, with minimum 20 million reads per sample, was performed using CLC Genomics Workbench software suit, followed by Gene Ontology and KEGG pathway analyses. Based on the number of the identified differentially expressed genes (DEGs), the peak response occurred at 48 hpi. Gene functioning in hormone signaling including ethylene, jasmonate, gibberellin, cytokinin and auxin, and those encoding NAC, WRKY, MYB and ERF transcription factors were identified; genes encoding enzymes in several biosynthesis pathways of potential antimicrobial secondary metabolites and cell wall modification proteins are among the consistently up-regulated DEGs. Genes encoding defense and stress related protein such as wall-associated receptor kinase (WAK), endochitinase (PR4), thaumatin (PR5)-like protein, laccase, mandelonitrile lyase and cyanogenic beta-glucosidase were also highly induced after 24 hpi. Compared to Arabidopsis foliar pathosystem involving necrotrophic pathogens, substantial similarity was observed regarding the molecular framework of defense responses in the root system of perennial Rosaceae crops. Triple-digit induction of two cytokinin hydroxylase encoding genes may suggest that cytokinin signaling is one of the unique aspects in apple root system in response to necrotrophic oomycetes. The differential responses in resistant and susceptible apple rootstock genotypes, and to other ARD pathogens, are currently being examined.