A phytochrome/phototropin chimeric photoreceptor promotes growth of fern gametophytes under limited light conditions.

This article focuses on the photoreceptor phytochrome 3/neochrome (phy3/neo) in the fern Adiantum capillus-veneris and its role in fern adaptation to low-light environments under forest canopies. The study demonstrates that phy3/neo localizes both at the plasma membrane and in the nucleus, where it interacts directly with Adiantum cryptochrome 3 (cry3), suggesting a coordinated regulation of light-mediated responses including phototropism, chloroplast photorelocation, and gametophyte growth. Loss-of-function mutants of phy3/neo exhibit delayed prothallium expansion and altered expression of the Cyclin-like gene AcCyc1, indicating phy3/neo’s involvement in cell cycle regulation during the gametophytic stage. These findings provide insight into the molecular mechanisms underlying fern shade adaptation and propose that phy3/neo’s dual localization and interaction with cryptochrome contribute to efficient light signaling in shaded habitats.