Molecular mechanism of drought resistance in oat roots revealed using integrated physiological and multi-omics analyses

Abstract: Oat (Avena sativa L.), a key forage crop, is highly susceptible to water deficit. Many studies have elucidated the mechanisms through which oat leaves respond to drought; however, little is known about these mechanisms in roots. We compared the physiological, transcriptomic, and metabolomic responses of a drought-tolerant oat cultivar (DA92-2F6, D) and a drought-sensitive cultivar (Longyan No.3, L3) under PEG-induced drought stress at 0, 6, 24, and 72 h of the root system *to drought stress. We found that drought stress significant increases in malondialdehyde (MDA) and hydrogen peroxide levels, with the most pronounced accumulation observed in L3. D varieties maintained significantly higher antioxidant enzyme activities (CAT, POD, SOD, APX; P < 0.05), which causes variations in drought resistance. Additionally, differences in gene expression and drought-resistance pathways between the two varieties were clarified using transcriptome analysis. Through a multi-omics joint analysis, flavonoid biosynthesis and plant hormone signals were identified as the core drought resistance pathways in oat roots. Candidate genes associated with drought response included CHS, C4H, SHT, CYP98A3, FLS, and CHIL (flavonoid biosynthesis); and AUX/IAA, GH3, B-ARR, DELLA, PP2C, SnRK2, JAZ, MYC2, CPK, and GS2 (hormone signaling). Marker metabolites (phlorizin, naringenin, sakuranetin, pinobanksin) affecting drought resistance were identified. In addition, exogenous phlorizin effectively enhanced the drought response of the sensitive genotype L3. This study provides useful data for investigating drought responses in plant root and offers theoretical support for plant breeding for drought resistance.