Chapter One - Regulatory Networks Acted Upon by the GID1–DELLA System After Perceiving Gibberellin

Abstract

Recent studies have revealed that DELLA proteins (DELLAs) interact with various kinds of transcription factors (TFs) and other kinds of proteins to regulate GA signaling. Here, we enumerate some of these DELLA interactors to show the multiple functions of DELLAs in the GA signaling pathway. Through interaction with TFs, DELLAs regulate the expression of many genes in an inhibitory or enhancing manner under various biological events including the crosstalk between GA and other phytohormones, and the development of organs and tissues. DELLA-interacting TFs can be categorized into two types in terms of the effect of DELLA on their transacting activity. The first group includes those that are inhibited by DELLAs in terms of their DNA-binding activity, which includes the phytochrome interacting factor family of proteins involved in hypocotyl elongation, chlorophyll biosynthesis, fruit patterning, and cotyledon expansion; squamosa promoter binding-like proteins involved in floral transition; ethylene insensitive 3 and EIN3-like 1 proteins involved in GA-ethylene crosstalk; brassinazole-resistant 1 involved in GA-brassinosteroid crosstalk; and jasmonate ZIM domain and MYC2 proteins involved in GA-jasmonate crosstalk. The second group includes those TFs that affected in terms of their transcriptional activity but not DNA-binding activity upon interaction with DELLA, which includes the ABA-insensitive 3 and ABI5 involved in GA-abscisic acid crosstalk, indeterminate domain involved in feedback regulation of GA signaling, and Botrytis-susceptible interactor proteins involved in DELLAs transrepression activity. We also mentioned that interaction of DELLAs with proteins besides TFs regulates the crosstalk between GA and strigolactone, and tubulin folding. The interaction of all of these various TFs and proteins with DELLAs strongly demonstrates that DELLA functions as a hub protein linking GA signaling to a myriad of biological events.