From methylglyoxal to pyruvate: a genome-wide study for the identification of glyoxalases and D-lactate dehydrogenases in Sorghum bicolor

Abstract

Background: The glyoxalase pathway is evolutionarily conserved and involved in the glutathione-dependent detoxification of methylglyoxal (MG), a cytotoxic by-product of glycolysis. It acts via two metallo-enzymes, glyoxalase I (GLYI) and glyoxalase II (GLYII), to convert MG into D-lactate, which is further metabolized to pyruvate by D-lactate dehydrogenases (D-LDH). Since D-lactate formation occurs solely by the action of glyoxalase enzymes, its metabolism may be considered as the ultimate step of MG detoxification. By maintaining steady state levels of MG and other reactive dicarbonyl compounds, the glyoxalase pathway serves as an important line of defence against glycation and oxidative stress in living organisms. Therefore, considering the general role of glyoxalases in stress adaptation and the ability of Sorghum bicolor to withstand prolonged drought, the sorghum glyoxalase pathway warrants an in-depth investigation with regard to the presence, regulation and distribution of glyoxalase and D-LDH genes. Result: Through this study, we have identified 15 GLYI and 6 GLYII genes in sorghum. In addition, 4 D-LDH genes were also identified, forming the first ever report on genome-wide identification of any plant D-LDH family. Our in silico analysis indicates homology of putatively active SbGLYI, SbGLYII and SbDLDH proteins to several functionally characterised glyoxalases and D-LDHs from Arabidopsis and rice. Further, these three gene families exhibit development and tissue-specific variations in their expression patterns. Importantly, we could predict the distribution of putatively active SbGLYI, SbGLYII and SbDLDH proteins in at least four different sub-cellular compartments namely, cytoplasm, chloroplast, nucleus and mitochondria. Most of the members of the sorghum glyoxalase and D-LDH gene families are indeed found to be highly stress responsive.Conclusion: This study emphasizes the role of glyoxalases as well as that of D-LDH in the complete detoxification of MG in sorghum. In particular, we propose that D-LDH which metabolizes the specific end product of glyoxalases pathway is essential for complete MG detoxification. By proposing a cellular model for detoxification of MG via glyoxalase pathway in sorghum, we suggest that different sub-cellular organelles are actively involved in MG metabolism in plants.

Glutathione Metabolism in Plants under Stress: Beyond Reactive Oxygen Species Detoxification

“…In plants, genome wide analyses show that GLXI- and GLXII-like proteins are encoded by multi-gene families [ 176 , 189 , 190 , 191 , 192 ] as opposed to the situation observed in the majority of prokaryotes and animals, where they occur as single genes [ 193 ]. In Arabidopsis and other species, expression analysis of these genes reveals that several members are differentially transcribed depending on the plant tissue, stage of development, and abiotic stress [ 176 , 189 , 190 , 191 , 192 ]. However, not all genes are predicted to encode for proteins with enzyme activity.…”

Serotonin and Melatonin Biosynthesis in Plants: Genome-Wide Identification of the Genes and Their Expression Reveal a Conserved Role in Stress and Development

“…The primer sequences used in this study have been provided in Supplementary Table S5. The qRT-PCR analysis was performed as described elsewhere [83]. normalization of transcripts, elongation factor 1-alpha (EF-1a) was used.…”

Interplay among Oxidative Stress, Methylglyoxal Pathway and S-Glutathionylation

“…Finally, cell ability to discard D-LAC by oxidizing it inside mitochondria [ 17 ] or exporting it to the extracellular phase is also important to avoid MGO accumulation. In plants, following D-LDH silencing, MGO increase, cytosolic GSH level decrease and growth inhibition have been observed [ 27 , 28 ]. Similarly, to what was found in plants, mammalian D-LDH activity could be equally important for the complete detoxification of MGO.…”