Transcriptional activator involved in cell elongation. Regulates the expression of a subset of genes involved in cell expansion by binding to the G-box motif. Homodimer (Probable). Interacts with IBH1. Expressed constitutively in roots, stems, and flowers. Plants over-expressing BHLH49 show increased hypocotyl and cotyledon lengths and increased flower size. May be due to a competing acceptor splice site.