Abstract
It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperms.
Highlights
Plants have evolved numerous ways to optimize photosynthetic light capture
Modern studies of phototropism began with experiments in monocotyledonous grasses by Charles Darwin and led to the discovery of the plant growth hormone auxin, establishing the concept that light perception at the shoot apex triggers differential bending in the tissues below
We show that the proximity of light perception and differential growth is conserved between monocots and dicots: in both plant types, differential growth is a consequence of lateral auxin movements across the shoot apex
Summary
Plants have evolved numerous ways to optimize photosynthetic light capture. Phototropism, the reorientation of growth towards light, is one of the most important of these adaptive processes [1]. Subsequent studies have since shown that phototropism arises from increased growth on the shaded side of the stem [3], owing to an accumulation of the phytohormone auxin [4]. Members of the PIN-FORMED family, named after the influorescence phenotype of the pin mutant, are the primary mediators of directional auxin fluxes that regulate plant development [8]. PIN3 is proposed to mediate lateral auxin fluxes by differentially restricting auxin to the vascular cylinder [6]. Consistent with this mode of action, PIN3 exhibits a subcellular localization on the inner side of bundle sheath cells [6]. PIN3 functions in apical hook opening [9], which may contribute to the delayed phototropism observed in etiolated pin seedlings [6,10]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
