Arabidopsis FIBRILLIN6 regulates carotenoid biosynthesis by directly promoting phytoene synthase activity

Abstract

Carotenoids are health-promoting plastidial isoprenoids with essential functions in plants as photoprotectants and photosynthetic pigments in chloroplasts. They also accumulate in specialized plastids named chromoplasts, providing color to non-photosynthetic tissues such as flower petals and ripe fruit. Carotenoid accumulation in chromoplast requires specialized structures and proteins such as fibrillins. Although fibrillins were first reported as structural components of carotenoid sequestering structures in chromoplasts, later work revealed roles in chloroplasts and other plastid types. However, the association of fibrillins with carotenoids in plastids other than chromoplasts has remained unexplored. Here we show that a member of the fibrillin family, FBN6, interacts with phytoene synthase (PSY, the first committed and rate-determining step of the carotenoid pathway) to promote its enzymatic activity. Transient overexpression of FBN6 in Nicotiana benthamiana leaves results in a higher production of phytoene, the product of PSY activity, whereas loss of FBN6 activity in Arabidopsis thaliana mutants dramatically reduces the production of carotenoids during seedling deetiolation and after exposure to high light. Our work hence demonstrates that fibrillins not only promote the accumulation of carotenoids but also their biosynthesis.

Involvement of Transcription Factors and Regulatory Proteins in the Regulation of Carotenoid Accumulation in Plants and Algae

“…119 Arabidopsis FBN6 could interact with PSY to promote its enzymatic activity, hence impacting the metabolic flux of the carotenoid pathway. 120 In melon, CmOR physically interacted with CmFBN1 and greatly stabilized CmFBN1, which stimulated plastoglobules proliferation and subsequently carotenoid accumulation in chromoplasts. 106 For algae, Dunaliella accumulates β-carotene in plastoglobules within the chloroplast, whereas H. pluvialis deposits astaxanthin in cytoplasmic lipid droplets 121 (Figure 1).…”

“…Recently, it was found that Arabidopsis FBN2 could interact with other proteins involved in various metabolic processes, including CCD4, a plastoglobules-associated enzyme involved in carotenoid degradation, but the functional relevance of the interaction with CCD4 was not explored Arabidopsis FBN6 could interact with PSY to promote its enzymatic activity, hence impacting the metabolic flux of the carotenoid pathway . In melon, CmOR physically interacted with CmFBN1 and greatly stabilized CmFBN1, which stimulated plastoglobules proliferation and subsequently carotenoid accumulation in chromoplasts .…”

Antioxidants of Non-Enzymatic Nature: Their Function in Higher Plant Cells and the Ways of Boosting Their Biosynthesis

“…The same authors have shown that homozygous Arabidopsis mutants with the FBN5 encoding gene knocked out were seedling-lethal, and the growth rate of transgenic plants with low FBN5-B levels was slower than that of wild-type plants. FBN6 was shown to interact with PSY and increase its enzymatic activity [72].…”