NtMYB1 and NtbZIP53 antagonistically regulates NtGA3ox2 and NtGA2ox8 mediating diverse GAs biosynthesis and tiny-plant in Narcissus tazetta

Miniaturization and multiple branching are characteristic features of horticultural plants. Gibberellin participates in regulating the size and branching of plant architecture. Gibberellin 3β hydroxylase (GA3ox) and Gibberellin 2β hydroxylase (GA2ox) is the pair of key enzymes for the homeostasis of active GA. However, how the transcriptional regulation of GA3ox and GA2ox and the synthesis of active GAs remains unknown. Here roles of narcissus NtMYB1 and NtbZIP53 in regulating the biosynthesis of diverse active GAs were addressed. Overexpression of NtMYB1 in Arabidopsis and Narcissus shows a tiny-type phenotype. The NtMYB1 co-expression network reveals that NtMYB1 or NtbZIP53 is closely related to NtKS1, NtGA20ox, NtGA2ox, and NtGA3ox in the GA biosynthetic pathway of narcissus. NtMYB1 can interact with NtbZIP53. Overexpression of NtMYB1 and NtMYB1/NtbZIP53 transgenic narcissus upregulated the expression of upstream genes NtKS1 and NtGA20ox of the GA biosynthesis pathway, however, NtMYB1 or NtbZIP53 and both directly targeted the promoters of NtGA3ox2 and NtGA2ox8 and antagonistically controlled NtGA3ox2 and NtGA3ox8 transcription and repressed GA1 biosynthesis, respectively. NtMYB1 recruiting NtbZIP53 enhance the repression of NtGA3ox2 and the activation of NtGA2ox8 to decline GA1/GA3 ratio and plant size in narcissus. It provides a conceptual basis for controlling the architecture of Chinese narcissus.