A Chloroplast ABC1-like Kinase Regulates Vitamin E Metabolism in Arabidopsis      

Abstract

In bacteria and mitochondria, ABC1 (for Activity of bc1 complex)-like kinases regulate ubiquinone synthesis, mutations causing severe respiration defects, including neurological disorders in humans. Little is known about plant ABC1-like kinases; in Arabidopsis (Arabidopsis thaliana), five are predicted in mitochondria but, surprisingly, six are located at lipid droplets in chloroplasts. These are a known site of prenylquinone (including tocopherol [vitamin E], phylloquinone [vitamin K] and plastoquinone) metabolism and contain a large proportion of the tocopherol cyclase (VTE1) required for vitamin E synthesis and recycling. Therefore, ABC1-like kinases may be involved in the regulation of chloroplast prenylquinone metabolism. Using a nontargeted lipidomics approach, we demonstrate that plants lacking the plastoglobule ABC1-like kinase ABC1K3 are defective both for the production of plastochromanol-8 (a plastoquinone-derived lipid antioxidant) and the redox recycling of a-tocopherol, whereas tocopherol production is not affected. All of these pathways require VTE1 activity. However, in the abc1k3 mutant, VTE1 levels are strongly reduced posttranscriptionally. We provide evidence that the ABC1-like kinase ABC1K3 phosphorylates VTE1, possibly stabilizing it at plastoglobules. However, ABC1K3 may also have other targets and be involved in a wider chloroplast regulatory network.

Unexpected roles of plastoglobules (plastid lipid droplets) in vitamin K 1 and E metabolism

“…This supports the idea that the accumulation of DMPBQ under HL is not sufficient to completely replace a-tocopherol and assume its membrane protective role in the thylakoid membranes [2,44,45]. vte2 displayed a simi-lar phenotype under short-term HL stress as vte1 [2].…”

“…At the protein level, however, Martinis et al [44,48 ] showed significantly lower contents of VTE1 in the abc1k1/pgr6 and abc1k3 mutants than in wt. These data suggest that ABC1K1/ PGR6 and ABC1-K3 stabilize VTE1 levels.…”

“…This was confirmed by in vitro experimentation. Moreover, VTE1 is a known phosphoprotein containing a phosphor-ylation hotspot near its N-terminus [44]. However, the range of other metabolic effects (reduced levels of b-carotene and lutein, altered PQ/PQH 2 ratio) observed in the mutant suggests that ABC1K1/PGR6 has many more targets.…”

A Comprehensive Analysis of Chromoplast Differentiation Reveals Complex Protein Changes Associated with Plastoglobule Biogenesis and Remodeling of Protein Systems in Sweet Orange Flesh

“…The Atabc1k7 mutant developed larger plastoglobules and lipid composition of the chloroplast membrane when compared with wide-type Arabidopsis (Manara et al, 2014(Manara et al, , 2015. Additionally, ABC1K1/3, as a complex, binds with phosphorylated tocopherol cyclase to affect plastoquinone metabolism (Lundquist et al, 2013;Martinis et al, 2013Martinis et al, , 2014Manara et al, 2014). Their double mutation also leads to abnormal accumulation of plastoglobules in Arabidopsis.…”

Genetically Programmed Changes in Photosynthetic Cofactor Metabolism in Copper-deficient Chlamydomonas

“…It would be interesting to test whether other stress situations also allow PC-8 accumulation and to distinguish the relevant regulatory mechanisms. In Arabidopsis, PC-8 levels are regulated by the activity of a type II NADPH dehydrogenase C1 (ortholog is NDA5 in Chlamydomonas) (47,48) and a plastid ABC1-like kinase (49).…”