Objective  Physiological role of NPR1 gene plays in the development of induced systemic resistance (ISR) in Oncidium hybridum was studied.

  Method  NPR1 of the orchid was cloned using RACE technique, and bioinformatics and phylogenenetic analyses on the gene conducted. After co-cultured with Piriformospora indica or treated with salicylic acid (SA) or methyl jasmonate (MeJA) to induce ISR, the orchids were analyzed for the treatment effect against soft rot disease caused by Erwinia chrysanthemi. And, expressions of NPR1 during the treatments were investigated.

  Result  Two full-length cDNA sequences were cloned. They were of a same type, one named OgNPR1-1 with a length of 1 804 bp encoding 555 amino acids, and the other, OgNPR1-2 1 902 bp encoding 556 amino acids. Their expressions were slightly upregulated by the inoculation of symbiotic P. indica. However, as both P. indica and E. chrysanthemi were present in the orchids, the expressions were significantly upregulated. It indicated that, in the presence of P. indica, the orchid plants became significantly more resistant to E. chrysanthemi inhibiting spread of the soft rot disease. On the other hand, the symbiosis of P. indica did not upregulated the expressions of the two genes more than the treatment by exogenous SA or MeJA on the orchids.

  Conclusion  The expression of NPR1 in the orchids inoculated with the symbiotic P. indica was significantly upregulated in the presence of E. chrysanthemi. Although the increased expression by P. indica was lower than what induced by exogenous SA or MeJA hormone treatment, nonetheless, the orchids benefitted from the symbiosis and became more resistance to the soft rot disease.