Methylglyoxal controls tomato fruit ripening by regulating ethylene biosynthesis

Methylglyoxal (MG), a toxic compound produced as a byproduct in several cellular processes such as respiration and photosynthesis, is well investigated for its deleterious effects, mainly through glycation of proteins during plant stress responses. However, very little is known about its impact on fruit ripening. In the present study, we report that MG levels are maintained at high level in green tomato fruits, which declines during fruit ripening inspite of a respiratory burst during this transition. We demonstrate that this decline is mainly mediated by glutathione-dependent MG detoxification pathway and primarily catalyzed by glyoxalase enzyme encoded by SlGLY14 gene. SlGLYI4 is a direct target of MADS-RIN and is induced during fruit ripening. Silencing of this gene leads to drastic MG overaccumulation at ripening-stages in the transgenic fruits and interferes with the ripening process. Further investigations show that MG plausibly glycates and inhibits key enzymes such as methionine synthase (MS) and S-adenosyl methionine synthase (SAMS) of ethylene biosynthesis pathway, thereby indirectly affecting fruit pigmentation and cell was metabolism. MG overaccumulation in several non-ripening or inhibited- ripening tomato mutant fruits suggests the tightly regulated MG detoxification process is crucial for normal ripening program. Overall, we underpin a SlGLYI4-mediated novel regulatory mechanism of MG detoxification controlling fruit ripening in tomato.