Lighting the Way Underground: Unraveling the Role of Dcphya in Carotenoid Synthesis in Carrot Taproots

Abstract

Light emerged as a paramount signal influencing the autotrophic growth of plants. Phytochrome A (PHYA) is characterized as light-labile, remaining stable in continuous far-red (FR)-rich light, playing a pivotal role in regulating seed germination, de-etiolation, and photomorphogenesis (including reducing hypocotyl length, chlorophyll, and carotenoid synthesis), as well as contributing to shade avoidance responses. Daucus carota L. (carrot), is known for its underground carotenoid accumulation while direct exposure to white light (WL) impairs both carotenoid synthesis and root development. By means of an RNA-seq analysis, light signal genes, such as DcPAR1, DcPIF3 and DcPHYA were found more expressed in the taproot grown underground. Here we present evidence on the functional characterization of DcPHYA, which exhibits 73% amino acid identity with AtPHYA in their functional domains, presents nuclear localization and a stable interaction with ELONGATED HYPOCOTYL 5 (DcHY5). Nicotiana tabacum overexpressing DcPHYA exhibit reduced hypocotyl length and reduced expression of the target genes NtPEPCK and NtPAR1 under FR, suggesting that DcPHYA is functional. Carrot transgenic lines with up to 50% reduced relative expression of DcPHYA have a reduction in carotenoid content between 65%-80% as well as in the relative expression of key genes in carotenoid synthesis, DcPSY1 and DcPSY2 in the taproot grown underground compared to wild-type plant. These results suggest that DcPHYA is functional and participates in carotenoid synthesis in the carrot taproot.

Keywords: DcPHYA, Carrot taproot, photomorphogenesis, carotenoid synthesis