InterPro domain: IPR044273

This entry represents a group of plant transcription factors that belongs to the basic helix-loop-helix (bHLH) family, including PIF3 from Arabidopsis, and APG/PIL15 from rice.

PIF3 (PHYTOCHROME INTERACTING FACTOR 3) is a phytochrome-interacting bHLH factor that targets G-box motifs through its bHLH domain [ 1 ]. PIF3 binds to phytochrome B, and the PAS domain of PIF3 is a major contributor to this interaction [ 2 ].

In rice PIL15 plays important roles in red light-mediated (phyA and/or phyB-dependent) signal transduction pathways [ 3 ]. APG interacts with POSITIVE REGULATOR OF GRAIN LENGTH 1 (PGL1), and this interaction represents a grain length and weight-controlling pathway in which APG is a negative regulator whose function is inhibited by PGL1 [ 4 ].

1. Direct targeting of light signals to a promoter element-bound transcription factor. Science 288, 859-63
2. Phytochrome B binds with greater apparent affinity than phytochrome A to the basic helix-loop-helix factor PIF3 in a reaction requiring the PAS domain of PIF3. Proc Natl Acad Sci U S A 97, 13419-24
3. Characterization of a set of phytochrome-interacting factor-like bHLH proteins in Oryza sativa. Biosci Biotechnol Biochem 71, 1183-91
4. Antagonistic actions of HLH/bHLH proteins are involved in grain length and weight in rice. PLoS One 7, e31325