Molecular Cloning and Characterization of a Serotonin N -Acetyltransferase Gene, xoSNAT3 , from Xanthomonas oryzae pv. oryzae .

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae ( Xoo ), is one of the top ten bacterial plant diseases worldwide. Serotonin N -acetyltransferase (SNAT) is one of the key rate-limiting enzymes in melatonin (MT) biosynthesis. However, its function in pathogenic bacteria remains unclear. In this study, a Xoo SNAT protein (xoSNAT3) that showed 27.39% homology with sheep SNAT was identified from a collection of 24 members of GCN5-related N -acetyltransferase (GNAT) superfamily in Xoo . This xoSNAT3 could be induced by MT. In tobacco-based transient expression system, xoSNAT3 was found localized on mitochondria. In vitro studies indicated that xoSNAT3 showed the optima enzymatic activity at 50 °C. The recombinant enzyme showed K m and V max values of 709.98 μM and 2.21 nmol/min/mg protein, respectively. Mutant △ xoSNAT3 showed greater impaired MT biosynthesis than the wild-type strain. Additionally, △ xoSNAT3 showed 14.06% less virulence and 26.07% less biofilm formation. Collectively, our results indicated that xoSNAT3 services as a SNAT involved in MT biosynthesis and pathogenicity in Xoo .