METABOLOMICS INSIGHTS INTO RICE STRESS RESPONSES UNDER CHANGING CLIMATE

Abstract

More than half a world relies on rice as the source of calories; however, it is facing mounting threats of heat, drought, flooding, salinity, cold and growing levels of atmospheric CO2 the dangers often do not happen in isolation but happen together. Understanding of molecular response of rice to multiple environmental stresses has become a major priority modern crop science. The review brings together existing metabolomics studies on rice responses to stress, the objective of which is to unravel shared metabolic responses to six major abiotic stresses, to establish the impact of soil typology on these responses, and to determine the key knowledge gaps that have a direct impact on breeding programmes. Available published metabolomic studies utilizing either gas chromatography/ mass spectrometry (GC-MS), liquid chromatography/ mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR) were analyzed and related to the soil-science literature with the aim of placing metabolic findings in real agronomic situations. It used evidence based on both the controlled experiments and free-air CO2 enrichment (FACE) field trials. In all stress conditions, proline, γ -aminobutyric acid (GABA), and raffinose -family oligosaccharides became conserved protective compounds, whereas a general inhibition of tricarboxylic -acid (TCA) intermediates indicated metabolic stress and resultant yield loss. Heat stress alters the biosynthesis of starch, resulting in chalky grains; drought stimulates the accumulation of proline and trehalose, which is regulated by soil texture; flooding shifts the carbon flux to fermentative materials; salinity induces the accumulation of glycine-betaine; cold changes lipid composition of the membrane; and the increased CO2 selectively downregulates the concentration of grain protein, zinc, and iron - a phenomenon enhanced by nitrogen deficiency in the soils. Many of the metabolites can currently meet the metabolite-assisted breeding selection criteria. Metabolomics is no longer just another descriptive narrative; it has developed into quantifiable, inheritable biomarkers with an actual potential to guide the creation of stress-resistant rice crops modified to cope with a climate that is growing more erratic.