Multiple phytohormones, including gibberellin (GA), abscisic acid (ABA), and indole-3-acetic acid (IAA), regulate seed germination. In this study, a barley aldehyde oxidase 1 (HvAO1) gene was identified, which is located near the SD2 (seed dormancy 2) region at the telomeric end of chromosome 5H. A doubled-haploid population (AC Metcalfe/Baudin) was used to characterize HvAO1 and validated its association with seed germination and malting quality. Aldehyde oxidase is predicted to catalyse the oxidation of various aldehydes, such as indoleacetaldehyde and abscisic aldehyde, into IAA and ABA, which is the final step of IAA/ABA biogenesis. This process influences the final IAA/ABA concentration in the seed, affecting the seed dormancy. Sequence analysis revealed substantial variations in the HvAO1 promoter regions between AC Metcalfe and Baudin. The combining seed germination tests, genetic variation analysis, gene expression, and phytohormone measurements showed that Baudin, which displays strong seed dormancy, has a specific sequence variation in the promoter region of the HvAO1 gene. This variation is associated with a higher expression level of the HvAO1 gene and an increased level of ABA than those in AC Metcalfe, which shows weak dormancy and lacks this sequence variation. In addition to its strong effect on the SD2 gene, HvAO1 shows excellent potential to fine-tune malting quality and seed dormancy, as evidenced by genotyping with HvAO1-specific markers, dormancy phenotypes, and malting quality. Our findings provide a new strategy for introducing favourable HvAO1 alleles to achieve the desired level of seed dormancy and high malting quality in barley.

Drought stress is one of the most severe environmental constraints to plant growth and crop productivity. Plant growth is greatly affected by drought stress, and plants, to survive, adapt to this stress by invoking different pathways. Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance to biotic and abiotic stresses, including drought stress, by affecting the physiological properties of the host plant. The fungus strongly colonizes the roots of maize (Zea mays L.) and promotes shoot and root growth under both normal growth conditions and drought stress. We used polyethylene glycol (PEG-6000) to mimic drought stress and found that root fresh and dry weight, leaf area, SPAD value, and leaf number were increased in P. indica-colonized plants. The antioxidative activities of catalases and superoxide dismutases were upregulated within 24h in the leaves of P. indica-colonized plants. Drought-related genes DREB2A, CBL1, ANAC072, and RD29A were upregulated in drought-stressed leaves of P. indica-colonized plants. Furthermore, after drought treatment, proline content increased, whereas accumulation of malondialdehyde (MDA), an indicator of membrane damage, decreased in P. indica-colonized maize. We conclude that P. indica-mediated plant protection against the detrimental effects of drought may result from enhanced antioxidant enzyme activity, proline accumulation, and expression of drought-related genes and lower membrane damage in maize plants.