Nitrate participates in the regulation of MdBT2-mediated MdCIbHLH1 protein stability. A, Protein stability of MdCIbHLH1 in response to nitrate. 35S:: MdCIbHLH1-GFP calli were incubated without nitrate (−N) and with nitrate (+N), respectively. The total proteins extracted from these calli samples were then used for immunoblotting (IB) assays using the anti-GFP antibody. B and C, IB assays were conducted using 35S::MdCIbHLH1-GFP treated with or without nitrate. IP, Immunoprecipitated.