Exploring traditional aus-type rice formetabolites conferring drought tolerance

Background:Traditional varieties and landraces belonging to the aus-type group of rice (Oryza sativaL.) are knownto be highly tolerant to environmental stresses, such as drought and heat, and are therefore recognized as a valuablegenetic resource for crop improvement. Using two aus-type (Dular, N22) and two drought intolerant irrigated varieties(IR64, IR74) an untargeted metabolomics analysis was conducted to identify drought-responsive metabolites associatedwith tolerance.Results:The superior drought tolerance of Dular and N22 compared with the irrigated varieties was confirmed byphenotyping plants grown to maturity after imposing severe drought stress in a dry-down treatment. Dular and N22did not show a significant reduction in grain yield compared to well-watered control plants, whereas the intolerantvarieties showed a significant reduction in both, total spikelet number and grain yield. The metabolomics analysis wasconducted with shoot and root samples of plants at the tillering stage at the end of the dry-down treatment. The datarevealed an overall higher accumulation ofN-rich metabolites (amino acids and nucleotide-related metabolites allantoinand uridine) in shoots of the tolerant varieties. In roots, the aus-type varieties were characterised by a higher reduction ofmetabolites representative of glycolysis and the TCA cycle, such as malate, glyceric acid and glyceric acid-3-phosphate.On the other hand, the oligosaccharide raffinose showed a higher fold increase in both, shoots and roots of the sensitivegenotypes. The data further showed that, for certain drought-responsive metabolites, differences between the contrastingrice varieties were already evident under well-watered control conditions.Conclusions:The drought tolerance-related metabolites identified in the aus-type varieties provide a valuable set ofprotective compounds and an entry point for assessing genetic diversity in the underlying pathways for developingdrought tolerant rice and other crops.