Bell-like homeodomain1 (BLH1) regulates ABA-mediated seed germination and early seedling development via interaction with KNAT3

Abstract

The phytohormone abscisic acid (ABA) regulates seed dormancy, germination, and seedling growth in response to environmental signals. Integration of environmental stimuli into intrinsic developmental programs is essential for optimal growth and development of plants. Here, we show that homeodomain transcription factors, known for key developmental regulators, are importantly involved in ABA-mediated seed dormancy and early seedling development. The expressions of two homeobox genes, BLH1 and KNAT3, were induced by RCAR-type receptor-triggered ABA signaling pathway. The blh1 and knat3 knockouts were less sensitive to ABA and salinity exposure during seed germination and early seedling development. In contrast, BLH1 overexpression led to hypersensitivity to ABA and salt stress. BLH1 induced ABA-responsive genes for seed germination such as ABI3 and ABI5. BLH1 interacted with KNAT3 and enhanced the retention of KNAT3 in the nucleus. BLH1 and KNAT3 synergistically induced the expression of ABA-inducible RD29B, while the disruption of the interaction between BLH1 and KNAT3 resulted in the loss of this synergism. Taken together, we propose a novel ABA signaling module in germination and seedling development governed by homeoproteins BLH1 and KNAT3