De novo organ regeneration is the process in which adventitious roots or shoots regenerate from detached or wounded organs. De novo organ regeneration can occur either in natural conditions, e.g. adventitious root regeneration from the wounded sites of detached leaves or stems, or in in-vitro tissue culture, e.g. organ regeneration from callus. In this review, we summarize recent advances in research on the molecular mechanism of de novo organ regeneration, focusing on the role of the WUSCHEL-RELATED HOMEOBOX11 (WOX11) gene in the model plant Arabidopsis thaliana. WOX11 is a direct target of the auxin signaling pathway, and it is expressed in, and regulates the establishment of, the founder cell during de novo root regeneration and callus formation. WOX11 activates the expression of its target genes to initiate root and callus primordia. Therefore, WOX11 links upstream auxin signaling to downstream cell fate transition during regeneration. We also discuss the role of WOX11 in diverse species and its evolution in plants.

Although many studies have elucidated the mechanisms by which different wavelengths of light (blue, red, far-red or ultraviolet-B [UV-B]) regulate plant development, whether and how green light regulates plant development remains largely unknown. Previous studies reported that green light participates in regulating growth and development in land plants, but these studies have reported conflicting results, likely due to technical problems. For example, commercial green LED light sources emit a little blue or red light. Here, using a pure green light source, we determined that unlike blue, red, far-red or UV-B light, which inhibit hypocotyl elongation, green light promotes hypocotyl elongation in Arabidopsis thaliana and several other plants during first the 2–3 days after planting. Phytochromes, cryptochromes, and other known photoreceptors do not mediate green light-promoted hypocotyl elongation, but the brassinosteroid signaling pathway is involved in this process. Green light promotes the DNA binding activity of BRI1-EMS-SUPPRESSOR 1 (BES1), a master transcription factor of the brassinosteroid pathway, thus regulating gene transcription to promote hypocotyl elongation. Our results indicate that pure green light promotes elongation via brassinosteroid signaling and acts as a shade signal to enable plants to adapt their development to a green-light-dominant environment under a canopy.