Figure 10.

A working model on SH1-regulated hypocotyl elongation through modulating of the CsUVR8-mediated signaling pathway. Under UVB-free white light or monochromic lights, the plants will undergo photomorphogenesis mediated by phytochromes (Pr) or cryptochromes (Cry) via the CSCOP1/CsHY5 pathway. In LDUVB-sensitive plants, the Sh1 gene has high level of expression. The abundant SH1 chromatin remodeler protein alters the accessibility of CsHY5 transcription factor to activate cell-elongation-related genes for hypocotyl elongation. LDUVB inhibits Sh1 expression, reduces its abundance, and thus SH1 protein level, which allows increased CsHY5 expression and more binding to the promoter of cell-elongation-related genes to inactivate their expression, therefore hypocotyl elongation. In UVB-insensitive plants, the expression of sh1 is always low regardless of the light conditions resulting in a similar outcome as Sh1 under LDUVB.