Abstract
BACKGROUND: Systematic acquired resistance (SAR) is an effective broad-spectrum defense mechanism that confers long-lasting protection against biotrophic pathogens trough defense related salicylic acid (SA) signaling. Gene(s) involved in SAR have been extensively studied in dicot plants; however, remains largely unresolved in monocot plants. NPR1, an evolutionary conserved gene, plays a central role in SAR, and PR-1 is widely used as a marker for effective SA signaling. RESULTS: We identified NPR1 and PR-1 homologous genes, PhaNPR1 and PhaPR1, from an economically important orchid, Phalaenopsis aphrodite, and characterized their roles in SA signaling and Cymbidium mosaic virus (CymMV) resistance. A phylogenetic analysis of NPR1 homologs showed that these genes appear to have evolved before angiospermy. Similar to Arabidopsis NPR1, PhaNPR1 was only moderately induced upon SA treatment and CymMV infection. Although PhaPR1 shows only 36% identity with AtPR1, its promoter shared conserved elements with those of other PR-1 genes, and it was induced upon SA treatment and CymMV infection. After CymMV infection, silencing on PhaNPR1 also reduced PhaPR1 expression; however, CymMV accumulation was not affected. CONCLUSIONS: In conclusion, after virus infection, PhaNPR1 is required for PhaPR1 induction, but plays little role in defense against CymMV.