Abstract
Similar to animals, plants possess ‘immune memory’ in response to invading pathogens that lead to enhanced defense reaction following pathogen exposure. Systemic acquired resistance (SAR) is a well-characterized type of plant immunity and is associated with coordinated expression of a set of pathogenesis-related (PR) genes and proteins also known as SAR markers. Induction of SAR in plants was shown to be initiated by group of chemicals and biological compounds known as SAR inducers that can be used for the management of important plant diseases. Elucidation and characterization of potential SAR inducers as potential elicitors that can protect papaya from the papaya dieback disease pathogen were carried out using HRPX protein, which was produced as a recombinant protein in an Escherichia coli system. Disease severity analysis in a glasshouse experiment indicated lower disease infection rates in the HRPX-treated plants than in water-treated plants. Selected SAR-associated defense gene expression was also shown to increase in treated plants, via quantitative real-time PCR analysis, confirming enhanced disease response through SAR activation. In this report, the selected recombinant protein was shown to activate the SAR mechanism in papaya for increased tolerance against papaya dieback disease, which was proven via physiological and molecular analysis.