CCD8

CCD8, or carotenoid cleavage dioxygenase 8, is an enzyme in the plant carotenoid cleavage dioxygenase family that participates in the biosynthesis of strigolactones, a class of plant hormones and rhizosphere signaling molecules. CCD8 acts in the strigolactone pathway alongside CCD7 to convert carotenoid-derived intermediates into carlactone, which is subsequently oxidized by MAX1 family cytochrome P450 enzymes to form active strigolactones.

Genetic and functional context: In Arabidopsis thaliana the gene is known as MAX4; in pea (Pisum sativum) as RMS1; in rice as D17 or HTD1, reflecting conservation across plants. CCD8 enzymes are typically localized to plastids where carotenoids are produced.

Physiological role: Strigolactones regulate shoot branching by inhibiting the outgrowth of axillary buds. Loss-of-function CCD8 mutants exhibit increased shoot branching and reduced strigolactone production, whereas application of synthetic strigolactones or genetic restoration of SL biosynthesis can restore normal branching.

Regulation and expression: CCD8 expression is often highest in roots and young shoots and can be induced under nutrient stress such as phosphate deficiency, reflecting a role in adaptive growth responses and rhizosphere signaling.

Impact and applications: Understanding CCD8 and the strigolactone pathway has implications for crop architecture and yields, as well as interactions with symbiotic fungi and parasitic plants through root exudates.