Amine oxidases of Arabidopsis thaliana are potential candidates of abscisic acid signalling

Abstract

Polyamines (PAs) are essential growth regulators present in all living organisms. PAs are oxidatively catabolized by two groups of amine oxidases namely copper-binding diamine oxidases (CuAO) and FAD-binding polyamine oxidases (PAO). Seven genes coding for CuAO and five genes coding for PAO are identified in Arabidopsis. PAs and amine oxidases play an array of roles in physiological processes of plant growth and development and in plant abiotic and biotic stress responses. Potential involvement of CuAO and PAO was tested for the role in nitric oxide (NO) signalling and ABA-mediated stress responses. Fluorimetric and fluorescence microscopic studies revealed that ABA-induced NO production was impaired in knockouts of CuAO1 and PAO2 compared to wild type (WT). The observations suggest possible functions of CuAO1 and PAO2 in ABA-mediated NO signalling. Further, ABA-induced H2O2 production was impaired in the knockouts indicating role of CuAO1 and PAO2 in H2O2 production. Morphological analysis with the knockouts and over-expressors showed differential sensitivity to exogenous application of ABA during seed germination, seedling establishment and root development. The results of ABA-induced NO production and growth responses suggest CuAO1 and PAO2 as potential signaling candidates linking ABA and NO.