Transcription factor that may act as negative regulator of phyB-dependent light signal transduction (PubMed:17485859). Transcription activator that acts as positive regulator of internode elongation. May function via regulation of cell wall-related genes. May play a role in a drought-associated growth-restriction mechanism in response to drought stress (PubMed:22984180). Interacts with PRR1 (PubMed:17485859, PubMed:21549224). Interacts with LF (PubMed:21549224). Highly expressed in the node portions of the stem. Expressed in the leaves and the basal part of shoots. Induced by light in dark-grown etiolated seedlings (PubMed:17485859). Circadian oscillation under 12 h light/12 h dark cycle conditions, with peaks in the middle of the light period (PubMed:17485859, PubMed:22984180). Down-regulated by cold and drought stresses (PubMed:22984180). Overexpression of PIL13 in transgenic plants promotes internode elongation. Expression of a chimeric repressor in transgenic plants results in short internode sections. Alteration of internode cell size causes the change in internode length. Belongs to the bHLH protein family.