Histone demethylation is crucial for proper chromatin structure and to ensure normal development, and requires the large family of Jumonji C (JmjC)-containing demethylases; however, the molecular mechanisms that regulate the substrate specificity of these JmjC-containing demethylases remain largely unknown. Here, we show that the substrate specificity of the Arabidopsis histone demethylase JMJ16 is broadened from Lys 4 of histone H3 (H3K4) alone in somatic cells to both H3K4 and H3K9 when it binds to the meiocyte-specific histone reader MMD1. Consistent with this, the JMJ16 catalytic domain exhibits both H3K4 and H3K9 demethylation activities. Moreover, the JMJ16 C-terminal FYR domain interacts with the JMJ16 catalytic domain and probably restricts its substrate specificity. By contrast, MMD1 can compete with the N-terminal catalytic domain of JMJ16 for binding to the FYR-C domain, thereby expanding the substrate specificity of JMJ16 by preventing the FYR domain from binding to the catalytic domain. We propose that MMD1 and JMJ16 together in male meiocytes promote gene expression in an H3K9me3-dependent manner and thereby contribute to meiotic chromosome condensation.

组蛋白去甲基化对于适当的染色质结构和确保正常发育至关重要，它需要包含Jumonji C（JmjC）的大家族脱甲基酶。然而，调节这些含JmjC的脱甲基酶的底物特异性的分子机制仍然是未知的。在这里，我们显示了拟南芥的底物特异性当组蛋白脱甲基酶JMJ16与肌​​细胞特异性组蛋白阅读器MMD1结合时，在体细胞中仅从组蛋白H3（H3K4）的Lys 4扩展到H3K4和H3K9。与此相一致，JMJ16催化域同时具有H3K4和H3K9脱甲基活性。此外，JMJ16 C端FYR结构域与JMJ16催化结构域相互作用，并可能限制其底物特异性。相比之下，MMD1可以与JMJ16的N末端催化结构域竞争与FYR-C结构域的结合，从而通过阻止FYR结构域与催化结构域的结合来扩展JMJ16的底物特异性。我们建议，MMD1和JMJ16一起在男性肌细胞中以H3K9me3依赖的方式促进基因表达，从而有助于减数分裂染色体的凝聚。