The obligatory role of ethylene in inducing ripening in fleshy fruits is well known. Due to the essential nature of ethylene in ripening, its biosynthesis and signaling pathways are well studied in fleshy fruits such as tomato. However, a complete understanding of the genetic regulatory mechanisms controlling ethylene-induced ripening program remains to be fully understood. Improved knowledge of such molecular regulatory events is crucial to develop effective biotechnological strategies for improving ripening traits such as fruit flavor, pigment accumulation, and fruit shelf-life. Varieties with prolonged fruit shelf-life can minimize the post-harvest loss of fruits and vegetables during transport and storage. Such superior varieties will also benefit farmers for their ROI and consumers for fresh and quality agri-products.
In a breakthrough collaborative research, a team of plant scientists jointly led by Dr. Rahul Kumar, University of Hyderabad, and Prof. Arun K. Sharma, University of Delhi, has identified a conserved mechanism that control tomato fruit ripening by inhibiting ethylene biosynthesis. The team found that several non-ripening mutants which do not ripe normally accumulate high levels of Methylglyoxal (MG), a toxic compound produced as a byproduct of several cellular processes, such as respiration and photosynthesis. MG is known to interfere with proteins function by non-enzymatically glycating them in both animals and plants. The main MG detoxification enyme system was found to be compromised in the non-ripening tomato mutants. The team developed both overexpression and gene-silenced lines of one of the ripening-associate glyoxalase enzyme (SlGLYI4) and demonstrated that silencing of this gene led to drastic MG overaccumulation at ripening-stages. This inhibited fruit ripening in the silenced lines and these fruits phenocopied the ripening phenotypes of non-ripening mutants. Further investigations showed 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, the study reported a novel mechanism regulating fruit ripening program and projected SlGLYI4 and its homologs, in other fruit species as potential candidates, to improve ripening traits in fleshy fruits.
Figure caption: Proposed model depicting the function of glyoxalase detoxification pathway and the impact of MG levels during tomato fruit ripening. The photosynthetically active mature green fruits accumulate high amounts of MG. However, at the onset of ripening, SlGLYI4 curtails the enhanced levels of MG associated with the respiratory burst and several other metabolic activities so that the ripening can proceed in a normal way. In the absence of the glyoxalase detoxification system at the time of fruit maturation, soaring amounts of MG can potentially inhibit the ethylene biosynthetic pathway at multiple levels, thereby leading to fruits incompetency to ripen. ACS2 1-aminocyclopropane-1-carboxylate synthase 2; SAM S-adenosyl methionine.
Due to the novelty and significance of the research findings, this work entitled ” Elevated methylglyoxal levels inhibit tomato fruit ripening by preventing ethylene biosynthesis” by Priya Gambhir et al. March 2034 (DOI: https://doi.org/10.1093/plphys/kiad142) is recently published in Plant Physiology, one of the top most scientific journal published by the American Society of Plant Biologists, USA.
The team members are:
- Priya Gambhir, Ph.D. scholar, Department of Plant Molecular Biology, UDSC, DU
- Vijendra Singh, Department of Plant Molecular Biology, UDSC, DU
- Adwaita Parida, Department of Plant Molecular Biology, UDSC, DU
- Utkarsh Raghuvanshi, Department of Plant Molecular Biology, UDSC, DU
- Shweta Sharma, Department of Plant Molecular Biology, UDSC, DU
- Arun Kumar Sharma, Department of Plant Molecular Biology, UDSC, DU
- Sudhir K. Sopory, International Centre for Genetic Engineering and Biotechnology, New Delhi
- Stuti Kujur, Department of Plant Sciences, UoH
- Rahul Kumar, Assistant Professor, Department of Plant Sciences, UoH