WRKY40, WRKY70, and Downy Mildew Resistant 6 (DMR6)-Like Oxygenase 1 are universal marker genes for the salicylic acid pathway in bananas

Abstract

Background: Banana, an important cash and staple crop worldwide, suffers from various biotrophic and hemi-biotrophic pathogens. In plants’ defense against these pathogens, the phytohormone salicylic acid (SA) plays a key role in the regulation of immune response. Using a specific set of SA-responsive genes as markers is frequently adopted to monitor the onset of SA-mediated immune response. However, reliable SA-responsive genes marker genes have not been well established in bananas. Results: From the transcriptome analysis of SA-treated ‘Pei-Chiao’ banana roots, we identified 19 up-regulated and 3 down-regulated genes. Four of the up-regulated genes previously reported to play crucial roles in SA-mediated immunity in other species were further analyzed for their applicability in different tissues and cultivars of bananas using real-time quantitative reverse-transcription PCR. The analysis showed that WRKY40, WRKY70, and Downy Mildew Resistant 6 (DMR6)-Like Oxygenase 1 (DLO1) were significantly induced upon SA treatment in both the leaves and roots of ‘Pei-Chiao’ (AAA genome), ‘Pisang Awak’ (ABB genome), and ‘Lady Finger’ (AA genome) bananas.Conclusions: The uncovering of common marker genes WRKY40, WRKY70, and DLO1 for SA response in different banana genome types provides the stepping stone for studies towards understanding of SA-mediated immune response in bananas.