Seed development-related expression of ARGONAUTE4_9 class of genes in barley: possible role in seed dormancy

Resistance to pre-harvest sprouting is an important breeding objective for cereal crops like barley and wheat. Seed dormancy, which determines the resistance or susceptibility to pre-harvest sprouting (PHS), is a complex trait. It is largely controlled by the antagonistic action of the plant hormones abscisic acid and gibberellic acid, but also has a large component of genotype x environment interaction. Recent studies have revealed a role for epigenetic changes through histone modification in controlling seed dormancy. However, the role of DNA methylation in seed development and dormancy is not known. In this study, we explored the role of ARGONAUTE4_9 class genes of the DNA methylation pathway in seed development and dormancy in barley. Our results show that the two AGO4_9 class genes in barley, i.e. AGO1002 and AGO1003, are preferentially expressed in ovaries at meiosis and in embryos 25 days after pollination (DAP). The expression of AGO1003 is two to fivefold higher than that of AGO1002 in these tissues, demonstrating differential expression of these genes. We also analysed the expression of AGO1003 in embryos of PHS-resistant and -susceptible varieties at 25 DAP and found a significant variation in the expression of this gene in seeds of dormant and non-dormant lines. The observed expression pattern of AGO1002 and AGO1003 suggests a possible role in sporogenesis and post-fertilization seed development. Indirectly these results imply a potential role of DNA methylation in seed development and seed dormancy.