InterPro domain: IPR043454

Root phototropism protein 3 (RPT3), also known as nonphototropic hypocotyl 3 (NPH3), and root phototropism 2 (RPT2) ( IPR029958 ) represent the founding members of a novel plant-specific family [ 1 ]. Three domains define the members of this family: an N-terminal BTB (broad complex, tramtrack, bric a brac) domain ( IPR000210 ), a centrally located NPH3 domain ( IPR027356 ), and a C-terminal coiled-coil domain.

NPH3 assembles with CUL3 to form a E3 complex that ubiquitinates phototropin 1 (phot1) and modulates phototropic responsiveness [ 2 , 3 ]. NPH3 is necessary for root and hypocotyl phototropisms, but not for the regulation of stomata opening or chloroplast relocation [ 4 ]. Coleoptile phototropism protein 1 (CPT1) is a rice orthologue of Arabidopsis NPH3 also required for phototropism [ 5 ]. This entry also includes DOT3 (AT5G10250) that is involved in shoot and primary root growth; DOT3 mutants produce an aberrant parallel venation pattern in juvenile leaves [ 6 ].

The NRL (for NPH3/RPT2-Like) family is formed by signaling molecules specificto higher plants. Several regions of sequence and predicted structuralconservation define members of the NRL family, with three domains being mostnotable: an N-terminal BTB domain, a centrally located NPH3domain, and a C-terminal coiled coil domain. The function of the NPH3 domainis not yet known [ 7 , 8 , 9 , 9 , 9 , 10 , 11 , 11 ].

1. Understanding phototropism: from Darwin to today. J. Exp. Bot. 60, 1969-78
2. Cullins 3a and 3b assemble with members of the broad complex/tramtrack/bric-a-brac (BTB) protein family to form essential ubiquitin-protein ligases (E3s) in Arabidopsis. J. Biol. Chem. 280, 18810-21
3. Modulation of phototropic responsiveness in Arabidopsis through ubiquitination of phototropin 1 by the CUL3-Ring E3 ubiquitin ligase CRL3(NPH3). Plant Cell 23, 3627-40
4. RPT2 is a signal transducer involved in phototropic response and stomatal opening by association with phototropin 1 in Arabidopsis thaliana. Plant Cell 16, 887-96
5. The Rice COLEOPTILE PHOTOTROPISM1 gene encoding an ortholog of Arabidopsis NPH3 is required for phototropism of coleoptiles and lateral translocation of auxin. Plant Cell 17, 103-15
6. Vein patterning screens and the defectively organized tributaries mutants in Arabidopsis thaliana. Plant J. 56, 251-63
7. Arabidopsis NPH3: A NPH1 photoreceptor-interacting protein essential for phototropism. Science 286, 961-4
8. RPT2. A signal transducer of the phototropic response in Arabidopsis. Plant Cell 12, 225-36
9. Regulation of phototropic signaling in Arabidopsis via phosphorylation state changes in the phototropin 1-interacting protein NPH3. J. Biol. Chem. 282, 19992-20001
10. Leaf positioning of Arabidopsis in response to blue light. Mol Plant 1, 15-26