Development and carotenoid synthesis in dark-grown carrot taproots require PHYTOCHROME RAPIDLY REGULATED1

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• Light regulates carotenoid synthesis via PHYTOENE SYNTHASE (PSY) in plants.
• Carrot taproots accumulate carotenoids but light inhibits their development and PSY gene expression.
• PHYTOCHROME RAPIDLY REGULATED1 (PAR1) is a transcriptional cofactor involved in plant photomorphogenesis.

Purpose of the Study:

• To investigate the role of carrot PHYTOCHROME RAPIDLY REGULATED1 (DcPAR1) in taproot development and carotenoid biosynthesis.
• To determine if DcPAR1 influences the expression of carotenogenic genes in carrots.
• To explore the functional conservation of PAR1 in regulating carotenoid synthesis and photomorphogenesis.

Main Methods:

• RNA sequencing to compare DcPAR1 expression in light-grown versus underground carrots.
• Overexpression of Arabidopsis AtPAR1 in carrot to assess effects on carotenoid production and DcPSY1 expression.
• In vivo binding assays and overexpression in Arabidopsis to study DcPAR1 interactions with PHYTOCHROME-INTERACTING FACTORs (PIFs) and PSY expression.
• Generation of DcPAR1 antisense carrot lines to evaluate the impact on carotenoid levels and taproot development.

Main Results:

• DcPAR1 shows higher expression in underground carrot taproots compared to light-grown ones.
• Overexpression of AtPAR1 in carrot enhances underground taproot carotenoid production and DcPSY1 expression.
• DcPAR1 binds to AtPIF7, and its overexpression in Arabidopsis increases AtPSY expression, carotenoid accumulation, and induces a photomorphogenic phenotype.
• DcPAR1 antisense lines exhibit significantly reduced carotenoid levels, decreased expression of carotenogenic genes, and impaired taproot development.

Conclusions:

• DcPAR1 plays a vital role in promoting secondary root development and carotenoid synthesis in underground carrot taproots.
• DcPAR1 acts as a positive regulator of carotenoid biosynthesis, potentially through interactions with PIFs.
• The findings suggest a conserved function of PAR1 in regulating plant growth, development, and secondary metabolite accumulation.