Major regulators of carotenoid biosynthesis have remained rather elusive even though the flux through the branch in the carotenoid pathway can affect plant development in response to environmental stimuli, such as light. Our recent investigations demonstrated that the production of the most abundant carotenoid in plants, lutein, is regulated by carotenoid isomerase (CRTISO) activity at a rate-limiting step of this branch point in carotenoid biosynthesis. CRTISO is required to isomerase cis-carotenes, such as tetra-cis-lycopene to all-trans-lycopene. In order to maintain permissive transcriptional regulation of CRTISO, active marks of histone lysine methylation are targeted to the promoter region by the SET DOMAIN GROUP8 (SDG8) methyltransferase. Mutants of SDG8 (ccr1) and CRTISO (ccr2) show an increase in shoot branching, which may be partly explained by limiting synthesis of the carotenoid-derived branching hormone, strigolactone. In this addendum, we demonstrate new functions for SDG8 in mediating branching in Arabidopsis roots. The roles that carotenoids and SDG8 play in root and shoot development begins to open new doors for investigating the regulation of carotenoid composition in response to epigenetic events.
Keywords: SDG8; arabidopsis; carotenoid; chromatin; epigenetic; histone; lutein; mRNA; methylation; regulation; root development; shoot branching; transcription.