Gene expression of pathogenesis-related protein during banana ripening and after treatment with 1-MCP

Pathogenesis-related (PR) proteins are generally considered as plant defense proteins associated with preventing or limiting pathogen and insect attack. Identification and characterization of a fruit PR1, the MaPR1a gene, is reported here for the first time from banana. The MaPR1a cDNA is 606 bp long and contains an open reading frame of 489 nucleotides encoding 162 amino acid residues. The deduced amino acid sequence of MaPR1a has a high level of identity with PR1 proteins from other plants. Southern blot as well as nucleotide sequence analyses using the Global Musa Genomics Consortium database suggests that MaPR1a is encoded by a multigene family in banana. Ethylene exposure of unripe mature banana fruit induced MaPR1a expression, which increased with ripening, and 1-methylcyclopropene (1-MCP) treatment prior to ethylene exposure inhibited expression. No expression was detected in any other tissue which suggests that MaPR1a gene family members are fruit-specific and ripening related. The 1506 bp proximal promoter of the gene shows the presence of cis-acting elements which could bind to sets of transcription factors as well as regulate jasmonic acid (JA) and salicylic acid (SA) signalling. Our expression analysis suggests that in addition to ethylene, JA and SA also induce expression of MaPR1a in fruit tissue.