Sulfoxidation Regulation of Musa acuminata Calmodulin (MaCaM) Influences the Functions of MaCaM-Binding Proteins

Sulfoxidation of methionine in proteins by reactive oxygen species can cause conformational alteration or functional impairment, and can be reversed by methionine sulfoxide reductase (Msr). Currently, only a few potential Msr substrates have been confirmed in higher plants. Here, we investigated Msr-mediated sulfoxidation regulation of calmodulin (CaM) and its underlying biological significance in relation to banana fruit ripening and senescence. Expression of MaCaM1 and MaMsrA7 was up-regulated with increased ripening and senescence. We verified that MaCaM1 interacts with MaMsrA7 in vitro and in vivo, and sulfoxidated MaCaM1 could be partly repaired by MaMsrA7 (MaMsrA7 reduces oxidized residues Met77 and Met110 in MaCaM1). Furthermore, we investigated two known CaM-binding proteins, catalase (MaCAT1) and MaHY5-1. MaHY5-1 acts as a transcriptional repressor of carotenoid biosynthesis-related genes (MaPSY1, MaPSY2 and MaPSY3) in banana fruit. MaCaM1 could enhance the catalytic activity of MaCAT1 and the transcriptional repression activity of MaHY5-1 toward MaPSY2. Mimicked sulfoxidation in MaCaM1 did not affect the physical interactions of the protein with MaHY5-1 and MaCAT1, but reduced the catalytic activity of MaCAT1 and the transcriptional repression activity of MaHY5-1. Our data suggest that sulfoxidation modification in MaCaM1 by MaMsrA7 regulates antioxidant response and gene transcription, thereby being involved in regulation of ripening and senescence of banana fruit.