ZmBSK1 positively regulates BR-induced H2O2 production via NADPH oxidase and functions in oxidative stress tolerance in maize

Abstract

Brassinosteroid (BR) has been indicated to induce the production of hydrogen peroxide (H₂O₂) in plants in response to various environmental stimuli. However, it remains largely unknown how BR induces H₂O₂ production. In this study, we found that BR treatment significantly raised the kinase activity of maize (Zea mays L.) brassinosteroid-signaling kinase 1 (ZmBSK1) using the immunoprecipitation kinase assay. ZmBSK1 could modulate the gene expressions and activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (EC 1.6.3.1) to modulate BR-induced H₂O₂ production. BR could enhance the interaction between ZmBSK1 and maize calcium/calmodulin-dependent protein kinase (ZmCCaMK), a previously identified substrate of ZmBSK1. The BR-induced phosphorylation and kinase activity of ZmCCaMK are dependent on ZmBSK1. Moreover, we showed that ZmBSK1 regulated the NADPH oxidase gene expression and activity via directly phosphorylating ZmCCaMK. Genetic analysis suggested that ZmBSK1-ZmCCaMK module strengthened plant tolerance to oxidative stress induced by exogenous application of H₂O₂ through improving the activities of antioxidant defense enzyme and alleviating the malondialdehyde (MDA) accumulation and electrolyte leakage rate. In conclusion, these findings provide the new insights of ZmBSK1 functioning in BR-induced H₂O₂ production and the theoretical supports for breeding stress-tolerant crops.

Keywords: Brassinosteroid; H(2)O(2); Maize; NADPH oxidase; Oxidative stress; ZmBSK1.