Abstract

Methylglyoxal (MG) is a potent cytotoxin which is produced as a by-product of various metabolic reactions in the cell. In conditions of abiotic stress in plants, MG production increases by 6 folds and it accumulates in the cell, ultimately leading to yield loss and productivity.  The major pathway which involves in MG detoxification comprises of two enzymes, Glyoxalase I and Glyoxalase II. Glyoxalase system converts MG to D-lactate and when overexpressed in plant system can improve the abiotic stress to tolerance significantly. Here in this study we are focusing on another enzyme D-LDH (D-Lactate dehydrogenase). It has been observed when, D-Lactate (the end product of Glyoxalase pathway) is accumulated at high level in the cell it can also be toxic.  D-LDH converts D-lactate to pyruvate, which goes to TCA cycle for energy production. Thus, MG detoxification involves three enzymes which work together to divert the toxic molecule towards energy production in times of unfavorable conditions. We have worked upon deciphering the role of these enzyme families in plants.For the first time, coexistence of different metal ion dependent Glyoxalase I enzymes in a single plant was found. Zn2+ dependent Glyoxalase I was found to provide better stress tolerance than Ni2+ dependent when overexpressed in E. coli and yeast.D-LDH yeast mutants were found to be sensitive to MG. A comparative study among GLYI, GLYII and D-LDH revealed AtGLYI and AtD-LDH to be more important than AtGLYII in conferring tolerance to multiple abiotic stresses.Thus, D-LDH is shown to be an integral part of MG detoxification system as well as helps in conferring abiotic stress tolerance.