Figure 8.

A simplified working model of phyB-dependent seed germination mediated by HID1. Previous studies have shown that upon activation by red light, the Pfr form of phyB mediates the rapid degradation of PIF1 as an early light response. This inhibits PIF1-induced transcription of ABA biosynthesis genes via a SOMNUS-dependent pathway. Following 48 h DAL, the expression of the noncoding RNA HID1 in the radicles is significantly increased in a phyB-dependent manner. HID1 directly and indirectly inhibits the expression of ABA biosynthesis genes to promote phyB-dependent seed germination. Solid arrows, direct positive regulation; Dashed arrows, indirect positive regulation; Solid bars, direct negative regulation; Dashed bars, indirect negative regulation.