NtMYB1 and NtNCED1/2 control abscisic acid biosynthesis and tepal senescence in Chinese narcissus (Narcissus tazetta)

Abstract

Chinese narcissus (Narcissus tazetta var. chinensis cv. 'Jinzhanyintai') is one of the 10 most famous traditional flowers of China, having a beautiful and highly ornamental flower with a rich fragrance. However, the flower longevity affects its commercial appeal. While petal senescence in Narcissus is ethylene-independent and abscisic acid-dependent, the regulatory mechanism has yet to be determined. In this study, we identified a R2R3-MYB gene (NtMYB1) from Narcissus tazetta and generated oeNtMYB1 and Ntmyb1 RNA interference mutants in Narcissus as well as an oeNtMYB1 construct in Arabidopsis. Overexpressing NtMYB1 in Narcissus or Arabidopsis led to premature leaf yellowing, an elevated level of total carotenoid, a reduced level of chlorophyll b, and a decrease in photosystem II fluorescence (Fv/Fm). A dual-luciferase assay and chromatin immunoprecipitation-quantitative PCR revealed that NtMYB1 directly binds to the promoter of NtNCED1 or NtNCED2 and activates NtNCED1/2 gene expression both in vitro and in vivo. Moreover, overexpressing NtMYB1 accelerated abscisic acid biosynthesis, up-regulated the content of zeatin and abscisic acid, and down-regulated the level of β-carotene and gibberellin A1, leading to petal senescence and leaf yellowing in Narcissus. This study revealed a regulatory process that is fundamentally different between non-photosynthetic organs and leaves.

Keywords: Narcissus; NtNCED; ABA biosynthesis; NtMYB1; metabolic flux; tepal senescence.