Glycolate oxidase gene family in Nicotiana benthamiana : genome-wide identification and functional analyses in disease resistance

Glycolate oxidase (GOX)-dependent production of H2O2 in response to pathogens and its function in disease resistance are still poorly understood. In this study, we performed genome-wide identification of GOX gene family in Nicotiana benthamiana and analyzed their function in various types of disease resistance. Sixteen GOX genes were identified in N. benthamiana genome. They consisted of GOX and HAOX groups. All but two NbGOX proteins contained an alpha_hydroxyacid_oxid_FMN domain with extra 43–52 amino acids compared to that of FMN-dependent alpha-hydroxyacid oxidizing enzymes (NCBI-CDD cd02809). Silencing of three NbGOX family genes NbHAOX8, NbGOX1 and NbGOX4 differently affected resistance to various pathogens including Tobacco rattle virus, Xanthomonas oryzae pv. oryzae (Xoo) and Sclerotinia sclerotiorum. Effect of these genes on resistance to Xoo is well correlated with that on Xoo–responsive H2O2 accumulation. Additionally, silencing of these genes enhanced PAMP-triggered immunity as shown by increased flg22-elicited H2O2 accumulation in NbGOX-silenced plants. These NbGOX family genes were distinguishable in altering expression of defense genes. Analysis of mutual effect on gene expression indicated that NbGOX4 might function through repressing NbHAOX8 and NbGOX1. Collectively, our results reveal the important roles and functional complexity of GOX genes in disease resistance in N. benthamiana.