Abstract
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.
Highlights
Glycolate oxidase (GOX/GLO) is a crucial enzyme in photorespiration, catalyzing the conversion of glycolate into glyoxylate in peroxisomes with the production of H2O21
N. benthamiana genome, BLASTp search was performed for five Arabidopsis GOX family protein sequences including three AtGOXs and two AtHAOXs against the N. benthamiana genome databases in SGN and University of Sydney, respectively
It is noteworthy that domain prediction analysis using NCBI-Conserved Domain Database (CDD) indicated that the alpha_hydroxyacid_oxid_FMN domain of all the identified N. benthamiana and Arabidopsis GOX sequences except NbHAOX3 and NbHAOX6 contained an extra fragment in the middle compared with that of FMN-dependent alpha-hydroxyacid oxidizing enzymes deposited in NCBI-CDD
Summary
Glycolate oxidase (GOX/GLO) is a crucial enzyme in photorespiration, catalyzing the conversion of glycolate into glyoxylate in peroxisomes with the production of H2O21. GOX is supposed to play a crucial role in plant disease resistance. Direct evidence supporting a role of GOX in plant disease resistance has been mainly reported from the studies in the model plant species Arabidopsis, rice and Nicotiana benthamiana to date. Tomato and cell death elicited by several R genes such as LOV1, RPP8 and Pto[5,20] These results indicate that GOX may play distinct roles in different types of plant disease resistance against various types of pathogens. Our results reveal that GOX genes play important roles in various types of resistance including PAMP-triggered immunity (PTI), host and nonhost resistance in N. benthamiana against different pathogens, and members of NbGOX gene family employ distinct defense pathways to modulate disease resistance
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