Probable transcription repressor that functions as negative regulator of phytochrome-mediated promotion of seed germination. Inhibits seed germination by regulating the expression of gibberellic acid (GA) and abscisic acid (ABA) metabolic genes. Does not regulate the expression of the DELLA genes RGA and RGA1. Activated by PIL5, a phytochrome-interacting basic helix-loop-helix transcription factor (PubMed:18487351). Represses directly JMJ20 and JMJ22 expression in the absence of red light (R) and in far-red (FR) conditions (PubMed:22483719). Interacts with MARD1/FLZ9 and RD21A. Specifically expressed in seeds. Increased levels of JMJ20 and JMJ22 in far-red (FR) conditions. Plants lacking SOM germinate in darkness, independently of various light regimens.