**4. Transcription response to SL signal**

Phytohormones induce a change in gene expression. This response is usually mediated by transcription factors. Until now, only one family of transcription factors has been identified as a downstream component in SL signaling, namely the TEOSINTE BRANCHED1/CYCLOIDEA/ PROLIFERATING CELL FACTOR1 family (TCP). In different species, single transcription fac‐ tors from this family, related to SL signal, were already characterized: Branched1 (BRC1) in *A. thaliana* [57], Fine Culm1/Teosinte Branched1 (FC1/OsTB1) in rice [58], TB1 in *Zea mays* L. [59] and PsBRC1 in *Pisum sativum* L. [60]. Expression of these genes is particularly strong in axillary buds, and mutations in these genes lead to an increased branched phenotype, which cannot be reverse by treatment with SLs. Elevated levels of *AtBRC1* expression were found after SL treatment and in the triple *smxl6/7/8* mutant, whereas decreased levels were found in SL biosynthesis mutants [53, 54]. Similar results were obtained for the *AtBRC1* target gene *Homeobox‐Leucine Zipper Protein 53* (*HB53*) [54], confirming that the transcription factors from TCP family act as elicitors in the SL‐signaling cascade. There remain, however, some differ‐ ences between mono‐ and dicot species. In *A. thaliana* and pea, the expression of *AtBRC1/ PsBRC1* is upregulated by SL treatment [60], whereas in rice and maize, the expression of *FC1/OsTB1* and *TB1* is not elevated by SL treatment [61, 62]. This difference is sometimes explained by assuming that monocots contain additional, still unknown, transcription factors that may act as *AtBRC1/PsBRC1* in dicots.
