<i>Glycine max</i> Jumonji C domain-containing proteins JMJ19/20 exhibit endopeptidase activity and interact with LUXs to mediate flowering time

Histone demethylases serve essential functions in plant growth and development across various species. However, their roles in Glycine max remain largely unexplored. This study identified GmJMJ19 and GmJMJ20, encoding JmjC domain-containing proteins. They exhibit circadian rhythmic expression patterns and interact with LUX ARRHYTHMO 2 (GmLUX2) both in vitro and in vivo. Although GmJMJ19/20 bind to histones, they lack conventional histone demethylase activity. Rather, GmJMJ19/20 function as endopeptidases that specifically cleave histone H3 peptides at unmethylated lysine 27 residues, in a manner independent of Fe²⁺ and α-ketoglutarate, the cofactors required for typical JmjC enzymes. Structural modeling supports the occlusion of the catalytic pocket that prevents access to methylated substrates. The simultaneous knockout of GmJMJ19/20 significantly delays flowering time. Comparative transcriptomic analyses reveal that the GmJM19/20-GmLUX2 module enhances GmFULc expression via independent of the canonical evening complex. Haplotype analysis suggests that GmJMJ19 underwent selection during domestication, potentially contributing to soybean geographical adaptation.