The Signal Transducer NPH3 Integrates the Phototropin1 Photosensor with PIN2-Based Polar Auxin Transport in Arabidopsis Root Phototropism

• Published in: The Plant cell 2012-02, Vol.24 (2), p.551-565
• Main Authors: Wan, Yinglang, Jasik, Jan, Wang, Li, Hao, Huaiqing, Volkmann, Dieter, Menzel, Diedrik, Mancuso, Stefano, Baluška, František, Lin, Jinxing
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Auxins; Bending; blue light; brefeldin A; Curvature; genetics; Hypocotyls; Indoleacetic Acids; Indoleacetic Acids - metabolism; Light; Light sources; metabolism; Mutation; Phosphoproteins; Phosphoproteins - genetics; Phosphoproteins - metabolism; Phototropins; Phototropins - metabolism; Phototropism; Phototropism - physiology; physiology; Plant cells; Plant Roots; Plant Roots - metabolism; Plant Roots - physiology; Plants; plasma membrane; Protein Serine-Threonine Kinases; Root growth; Roots; Seedlings; Signal Transduction; transporters
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.111.094284

Under blue light (BL) illumination, Arabidopsis thaliana roots grow away from the light source, showing a negative phototropic response. However, the mechanism of root phototropism is still unclear. Using a noninvasive microelectrode system, we showed that the BL sensor phototropini (phot1), the signal transducer NONPHOTOTROPIC HYPOCOTYL3 (NPH3), and the auxin efflux transporter PIN2 were essential for BL-induced auxin flux in the root apex transition zone. We also found that PIN2-green fluorescent protein (GFP) localized to vacuole-like compartments (VLCs) in dark-grown root epidermal and cortical cells, and phot1/NPH3 mediated a BL-initiated pathway that caused PIN2 redistribution to the plasma membrane. When dark-grown roots were exposed to brefeldin A (BFA), PIN2-GFP remained in VLCs in darkness, and BL caused PIN2-GFP disappearance from VLCs and induced PIN2-GFP-FM4-64 colocalization within enlarged compartments. In the nph3 mutant, both dark and BL BFA treatments caused the disappearance of PIN2-GFP from VLCs. However, in the photi mutant, PIN2-GFP remained within VLCs under both dark and BL BFA treatments, suggesting that photi and NPH3 play different roles in PIN2 localization. In conclusion, BL-induced root phototropism is based on the phot1/NPH3 signaling pathway, which stimulates the shootward auxin flux by modifying the subcellular targeting of PIN2 in the root apex transition zone.