Reduced expression of the genes encoding chloroplast-localized proteins in a cold-resistant bri1 (brassinosteroid-insensitive 1) mutant.

We showed that constitutive activation of the stress-inducible genes led to the endogenous difference to cold tolerance in the bri1-9 mutant and in the BRI1-GFP plants compared to the wild type. In order to get more insight into the balance between growth and stress resistance, we analyzed the cellular localization of the proteins encoded by the genes previously reported as up or downregulated in the bri1-9 and BRI1-GFP plants. We found that the genes responsible for the chloroplast-localized proteins are markedly downregulated in bri1-9, and the proteins encoded by them are involved with chloroplast development, metabolism, and the photosynthetic regulation that is an essential function of chloroplast in the plants cells during active growing periods. These imply that subsets of gene products that are yet uncharacterized modulate the metabolic and signaling processes that are occurring in the chloroplast, leading to the balanced growth and response to abiotic stresses including light stimulus.