Tomato photorespiratory glycolate-oxidase-derived H2O2 production contributes to basal defence against Pseudomonas syringae

Despite being essential for C-3 plants, photorespiration is believed to cause a significant crop yield loss even under future climates. However, how photorespiration affects plant basal defence still remains largely unknown. Here, we studied the involvement of photorespiration in tomato-Pseudomonas syringae pv. tomato DC3000 interaction focusing on three photorespiratory genes. Inoculation with P.syringae increased photorespiration rate (Pr) and expression of glycolate oxidase (GOX2), serine glyoxylate aminotransferase (SGT) and serine hydroxyl methyltransferase (SHMT1); however, inhibition of photorespiration by isonicotinic acid hydrazide decreased tomato basal defence against P.syringae. Furthermore, silencing of GOX2, SGT or SHMT1 genes in tomato decreased Pr but increased susceptibility to P.syringae, whereas transient overexpression of GOX2, SGT or SHMT1 in tobacco increased basal defence. Further study revealed that salicylic acid (SA) signalling is involved in GOX2-mediated, SGT-mediated and SHMT1-mediated defence. Moreover, H2O2 pretreatment remarkably alleviated the GOX2 silencing-induced depression in basal defence and SA signalling, whereas it had no effect on that of SGT-silenced and SHMT1-silenced plants. Taken together, these results suggest that H2O2 is critical for GOX2-modulated but not SGT-modulated or SHMT1-modulated SA signalling and subsequent basal defence against P.syringae. This work deepens the understanding of photorespiration-involved defence responses to bacterial attack in plants. Although photorespiration, an essential process in C-3 plants, has been implicated in the defence response of plants against pathogens, its role in plant basal defence still remains largely unknown. In this study, we investigated the involvement of photorespiration in tomato-Pseudomonas syringae pv. tomato DC3000 interaction focusing on three photorespiratory genes, namely glycolate oxidase (GOX2), serine glyoxylate aminotransferase (SGT) and serine hydroxyl methyltransferase (SHMT1). Results showed that inoculation with P.syringae increased photorespiration rate and expression of GOX2, SGT and SHMT1, while inhibition of photorespiration decreased tomato basal defence against P.syringae. Further investigation using virus-induced gene silencing and transient overexpression of those genes reveals that H2O2 is critical for GOX2-modulated but not SGT-modulated or SHMT1-modulated SA signalling and subsequent basal defence against P.syringae.