Blue light exposure intensifies leaf red pigmentation and enhances oxidative stress tolerance in the ornamental bromeliad Neoregelia ‘Fireball’

Abstract

Neoregelia is a genus of attractive, eye-catching foliage plants in the family Bromeliaceae. Blue light globally regulates multiple biological processes and secondary metabolism in plants. Recently, addition of blue light to the spectrum was reported to intensify pigmentation in some ornamental pot plants. Nevertheless, how blue light influences leaf red pigmentation and oxidative stress tolerance in Neoregelia is unclear. In this study, we performed RNA-seq analysis and a series of assays related to biological, physiological, and phenotypic characteristics. We found that exposure to blue light not only inhibits chlorophyll biosynthesis and accelerates the degradation of chlorophylls, but also up-regulates several flavonoid biosynthesis genes and significantly increases the accumulation of anthocyanins in Neoregelia ‘Fireball’ plants. Ultimately, this response leads to the presence of pure dark red leaves. We also found that blue light enhances oxidative stress tolerance in Neoregelia by promoting the expression of antioxidant-related genes and the accumulation of more proanthocyanidins (PAs). Our results also showed that blue light plays a positive role in lignin biosynthesis by activating the transcription of lignin biosynthesis-related genes in Neoregelia plants exposed to blue light. Furthermore, co-expression network analyses of RNA-seq data indicated that NfWRKY70 may be a key gene involved in the intensified leaf red pigmentation and enhanced oxidative tolerance caused by blue light exposure. Our findings provide novel insights into the regulatory mechanisms underlying blue light-induced leaf red pigmentation and oxidative tolerance, and offer new clues for the coordination between flavonoid and lignin biosynthesis in the plant phenylpropanoid biosynthetic pathway.