Wheat plastidial methionine sulfoxide reductase MSRB3.1 interacts with haem oxygenase 1 to improve osmotic stress tolerance in wheat seedlings

Abstract

Methionine (Met) oxidation leads to a mixture of the R and S stereoisomers of Met sulfoxide (Met-SO), which are reduced in both their free and protein-bound forms by Met-SO reductase (MSR) enzymes. To the best of our knowledge, no information currently exists on function and substrates of wheat MSRB3.1, the gene of which is induced by drought, predominantly in the leaf. In the present study, we found that the TaMSRB3.1 protein localised in the chloroplast and specifically reduced Met-R-SO to Met. Total MSR enzyme activity levels were enhanced significantly in Triticum aestivum and Arabidopsis thaliana transgenic lines overexpressing TaMSRB3.1. Characterisation of these lines, as well as Arabidopsis msrb3 and TaMSRB3.1/msrb3 strains indicated that TaMSRB3.1 contributes to plant tolerance to osmotic stress. Constitutively expressed TaMSRB3.1 led to inhibition of reactive oxygen species (ROS) accumulation by enhancing ROS-removal enzyme activity, and an increase in the levels of endogenous abscisic acid (ABA) and the sensitivity of stomatal guard cells to exogenous ABA. Further analyses by means of yeast two-hybrid screening, bimolecular fluorescence complementation and co-immunoprecipitation assays revealed that wheat haem oxygenase 1 (TaHO1) may be a substrate of TaMSRB3.1. Furthermore, TaMSRB3.1 and TaHO1 were found to be expressed in the leaves, their proteins localised within the chloroplasts, and both acted in osmotic response, according to the present and previous studies. Finally, TaMSRB3.1 overexpression in the Arabidopsis hy1-100 mutant was not able to rescue its sensitivity to osmotic stress. In summary, our results suggest that TaMSRB3.1 and TaHO1 interact with each other, and may activate ROS and ABA signalling under osmotic stress.