Isolation and characterization of two NPR1 genes in banana

Abstract

The protein encoded by the Nonexpressor of pathogenesis-related gene 1 (NPR1) also referred to as Non inducible immunitiy 1 (NIM1) or Salicylic acid insensitive 1 (SAI1) is a co-transcriptional regulator. The NPR1 gene plays a pivotal role in conferring broad spectrum resistant to plants. Elicitors like salicylic acid and pathogens coupled with the accumulation of reactive oxygen species influence its activation in the cytoplasm. The downstream activity of the NPR1 gene necessitates its translocation to the nucleus and an interaction with other transcription factors with a ‘TGAC’ core sequence for the induction of Pathogenesis-related genes. In this study I identified and isolated homologues of genes encoding the NPR1 protein in banana (Musa sp.). Southern blot analysis revealed the possible existence of more than one Musa NPR1 gene in four different banana cultivars. Furthermore, two banana NPR1 gene fragments designated (MNPR1A and MNPR1B) were isolated and their full lengths recovered and deposited in the gene bank. A preliminary phylogenetic analysis of Musa NPR1 revealed that the two newly isolated banana genes grouped closely with other monocot NPR1 genes. The two identified MNPR1-sequences differed greatly in their expression profile using quantitative real time polymerase chain reaction following either salicylic acid or methyl jasmonate treatment or treatment with Fusarium oxysporum Schlecht f. sp. cubense (Smith) Snyd. MNPR1A was expressed after Fusarium treatment with higher and earlier expression in the Fusarium-tolerant banana cultivar GCTCV-218 than in the Fusarium-susceptible banana cultivar Grand Naine. In comparison, MNPR1B was highly responsive to salicylic acid, but not to methyl jasmonate treatment, in both the tolerant banana cultivar GCTCV-218 and the susceptible banana cultivar Grand Naine. Expression of the MNPR1 genes correlated to Pathogenesis-related gene expression known to be involved in fungal resistance. It was found as a new result in this study that reduced sensitivity to Fusarium in GCTCV-218 might be partially attributed to the higher and an earlier expression of both MNPR1A and Pathogenesis-related-1 genes in this cultivar after Fusarium treatment.