Molecular mechanism of phytohormones regulating dormancy and germination of barley seeds

Under adverse conditions such as continuous rainfall or high humidity, mature grains are prone to pre-harvest sprouting (PHS) on the parent plant, significantly impacting crop yield and quality. While abscisic acid (ABA) and gibberellin (GA) are well-known regulators of seed germination, the molecular mechanisms by which other phytohormones influence this process remain underexplored. A germination test of 236 barley varieties showed a germination index range of 5.22 to 97.17, indicating extensive genetic diversity. Hormone treatments on fast-germinating Harrington and slow-germinating Stirling revealed that ABA, cytokinin, and salicylic acid inhibited germination, whereas GA and ethylene promoted it. Endogenous hormone quantification indicated that variations in PHS resistance between Harrington and Stirling were primarily due to differences in ABA, GA, auxin, and cytokinin levels. Transcriptomic analysis of barley embryonic tissues identified 260 hormone-responsive differentially expressed genes, with 54 of these genes showing specificity in their expression during germination. Comparative resequencing data from two pairs barley varieties exhibiting contrasting germination traits revealed 19 genes with substantial genetic variation in their coding regions, implicating these genes in the regulation of barley germination properties.