Long Hypocotyl 1 mediates light regulation of adventitious root development in Arabidopsis

Adventitious root (AR) formation is controlled by both endogenous and environmental cues. Light is an important environmental factor that has been reported to promote plant root development. However, knowledge about the mechanisms controlling light-mediated AR formation in etiolated hypocotyl cuttings is not fully understood. In this study, we report that a light-induced photomorphogenic gene Long Hypocotyl 1 (HY1), regulates AR formation in Arabidopsis and rice. In Arabidopsis, plastid-localized AtHY1 in pericycle cells was capable of activating AR formation. Transcriptome profiling and genetic evidence revealed that Phytochrome B (AtPHYB) and Long Hypocotyl 5 (AtHY5) act downstream of HY1 to regulate AR formation, through the stimulation of auxin signaling and transport. However, in rice, AR emergence at stem node is inhibited by light upon submergence, opposite to its effects in Arabidopsis. We further showed that defective mutants of OsHY1, OsPHYB and OsHY5 showed enhanced AR emergence by upregulating the expression of OsGH3s and OsPIN1 genes. These findings uncover a opposite role of HY1 on AR development in responses to light between Arabidopsis and rice. Overall design: Dark to light treatment for 0, 12, and 24h bwteen hy1 and WT