Sulfoxidation modification of NON-RIPENING (NOR) transcription factor is involved in the regulation of fruit ripening in tomato

Transcription factors (TFs) are important regulators of plant growth and development and responses to stresses. TFs themselves are also susceptible to multiple post-translational modifications (PTMs). Relatively, redox-mediated PTM of TFs in plants is not well elucidated. Here, we found that NON-RIPENING (NOR), a master TF regulating tomato fruit ripening, is a target of SlMsrE4 or SlMsrB2, the methionine sulfoxide reductase A and B in tomato, respectively. Methionine oxidation in NOR, i.e. sulfoxidation, or mimicking sulfoxidation by mutating Met138 to glutamine, leads to the decreased DNA-binding capacity and transcriptional regulatory activity in vitro. On the other hand, SlMsrE4 and SlMsrB2 can partially repair oxidized-NOR and restore its DNA-binding capacity. Genetic transformation of the nor mutant with NOR genomic DNA almost completely rescues the ripening phenotype. However, transformation of nor with NOR-M138Q, the mimicked methionine sulfoxidation, inhibits the restore of fruit ripening phenotype, and this is associated with the decreased DNA-binding and transcriptional activation of numerous ripening-related genes. Taken together, these findings uncover a novel mechanism by which Msr-mediated redox modification of NOR regulates the expression of ripening-related genes, thereby influencing tomato fruit ripening. To our knowledge, this is the first report that redox modification of TF regulates fruit ripening.nor is a NOR mutant, the phenotype is obstructed by maturity; NOR-12 is a rotational NOR in NOR mutant, the phenotype is a mature inhibition phenotype that basically restores nor mutant; Nor-18 is a rotation of NOR-M138Q in nor mutant, phenotype with the effect of restoring maturity, but the recovery efficiency is lower than the swing NOR.