Interaction of abscisic acid and auxin on gene expression involved in banana ripening

Phytohormones regulate numerous aspects of plant growth and development. Green-mature banana fruit were treated with deionized water (control), abscisic acid (ABA), indole-3-acetic acid (IAA) and ABA + IAA, respectively, to investigate the role of ABA and IAA in fruit ripening. Results showed that ABA accelerated fruit ripening, but IAA delayed the process. However, treatment of ABA + IAA showed little difference in fruit color and firmness. The acceleration of ABA and delay of IAA on banana ripening process seems to be neutralized by ABA + IAA. Digital gene expression revealed that ABA + IAA treated fruit maintained the similar color phenotype with the control by regulating the expression of chlorophyll degradation-related gene PaO (GSMUA_Achr6G25590_001), and carotenoid biosynthesis-related genes DXR (GSMUA_Achr3G20790_001) and PSY (GSMUA_Achr2G12480_001, GSMUA_Achr4G17270_001, GSMUA_Achr4G17290_001). Moreover, ABA + IAA treated fruit maintained the similar softening phenotype with the control by adjusting the expression of pectin degradation-related genes PME (GSMUA_Achr3G05740_001) and PL (GSMUA_Achr6G28160_001, GSMUA_Achr7G04580_001). ABA + IAA treatment nearly abolished the action of individual ABA or IAA through equilibrating the expression of specific genes involved in chlorophyll degradation, carotenoid biosynthesis and pectin degradation pathways in the postharvest ripening of banana. The interaction between ABA and IAA might exercise as an antagonistic mechanism of neutralizing the specific gene expression either induced by ABA or reduced by IAA in the postharvest ripening of banana.