Identification of genes induced by Venturia nashicola in indigenous Korean pear ‘Hwangsilri’

Abstract

Indigenous Korean pear ‘Hwangsilri’ leaves were inoculated with Venturia nashicola to build expressed sequence tags (ESTs) database as resources for transcripts induced in the inoculated leaves. After performing subtractive suppression hybridization using cDNA of the inoculated and uninoculated leaves harvested at 1, 48, and 96 hours after inoculation, 159 (1 hour), 384 (48 hours), and 110 clones (96 hours) were selected and sequenced. BLASTX searches each cDNA library against Genbank revealed 15, 50, and 22 unique sequences at 1, 48, and 96 hours after inoculation, respectively. Most highly represented ESTs at 1 hour after inoculation were photosynthesis- and senescence-related genes such as light harvesting chlorophyll a/b binding protein, ribulose-bishosphate carboxylase/oxyganase, and senescence-associated protein. Cytochrome P450-like TATA box binding proteins and manganese superoxide dismutase associated with the defense response, biotic and abiotic stresses were differentially expressed at 1 hour after inoculation. Although more than 50% of ESTs at 1 and 48 hours after inoculation were also associated with photosynthesis- and carbon fixation-related genes, defense-related genes were annotated as 14 clones at 48 hours after inoculation. Six ESTs associated with pathogen-defense and biotic and abiotic stresses were expressed only at 48 hours after inoculation. At 96 hours after inoculation, seven ESTs were involved in defense-response and biotic and abiotic stresses, and three out of the seven ESTs such as cyclophilin, F-box family, and leucine-rich repeat receptor-like kinase (LRR-RLK) were uniquely expressed. Quantitative real-time polymerase chain reaction analysis revealed that the transcripts for aldo-keto reductase (AKR) and LRR-RLK were highly expressed in the incompatible interaction. AKR gene was more highly expressed in resistant cultivar ‘Hwangsilri’ and moderately susceptible one ‘Gamcheonbae’ than in other cultivars. LRR-RLK showed differentially higher expression pattern in inoculated than in uninoculated leaves of susceptible cultivars including ‘Gamcheonbae’ and ‘Hwangkeumbae’. The ARK and LRRRLK genes were found to be associated with plant defense mechanism. However, more detailed further study using transformants introgressed these genes is required to understand how these genes are expressed and regulated by infection with V. nashicola.