OR, a Natural Variant of OR, Specifically Interacts with Plastid Division Factor ARC3 to Regulate Chromoplast Number and Carotenoid Accumulation.

Chromoplasts are colored plastids that synthesize and store massive amounts of carotenoids. Chromoplast number and size define the sink strength for carotenoid accumulation in plants. However, nothing is known about the mechanisms controlling chromoplast number.

1-Aminocyclopropane-1-carboxylic acid oxidase reaction mechanism and putative post-translational activities of the ACCO protein.

1-Aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACCO) catalyses the final step in ethylene biosynthesis converting ACC to ethylene, cyanide, CO2, dehydroascorbate and water with inputs of Fe(II), ascorbate, bicarbonate (as activators) and oxygen. Cyanide activates ACCO. A 'nest' comprising several positively charged amino acid residues from the C-terminal α-helix 11 along with Lys158 and Arg299 are proposed as binding sites for ascorbate and bicarbonate to coordinately activate the ACCO reaction.

Chloroplast division protein ARC3 regulates chloroplast FtsZ-ring assembly and positioning in arabidopsis through interaction with FtsZ2.

Chloroplast division is initiated by assembly of a mid-chloroplast FtsZ (Z) ring comprising two cytoskeletal proteins, FtsZ1 and FtsZ2. The division-site regulators ACCUMULATION AND REPLICATION OF CHLOROPLASTS3 (ARC3), MinD1, and MinE1 restrict division to the mid-plastid, but their roles are poorly understood. Using genetic analyses in Arabidopsis thaliana, we show that ARC3 mediates division-site placement by inhibiting Z-ring assembly, and MinD1 and MinE1 function through ARC3.

FtsHi1/ARC1 is an essential gene in Arabidopsis that links chloroplast biogenesis and division.

The Arabidopsis arc1 (accumulation and replication of chloroplasts 1) mutant has pale seedlings and smaller, more numerous chloroplasts than the wild type. Previous work has suggested that arc1 affects the timing of chloroplast division but does not function directly in the division process. We isolated ARC1 by map-based cloning and discovered it encodes FtsHi1 (At4g23940), one of several FtsHi proteins in Arabidopsis.

In vivo quantitative relationship between plastid division proteins FtsZ1 and FtsZ2 and identification of ARC6 and ARC3 in a native FtsZ complex.

FtsZ1 and FtsZ2 are phylogenetically distinct homologues of the tubulin-like bacterial cell division protein FtsZ that play major roles in the initiation and progression of plastid division in plant cells. Both proteins are components of a mid-plastid ring, the Z-ring, which functions as a contractile ring on the stromal surface of the chloroplast IEM (inner envelope membrane). FtsZ1 and FtsZ2 have been shown to interact, but their in vivo biochemical properties are largely unknown.

Effects of mutations in Arabidopsis FtsZ1 on plastid division, FtsZ ring formation and positioning, and FtsZ filament morphology in vivo.

In plants, chloroplast division FtsZ proteins have diverged into two families, FtsZ1 and FtsZ2. FtsZ1 is more divergent from its bacterial counterparts and lacks a C-terminal motif conserved in most other FtsZs. To begin investigating FtsZ1 structure-function relationships, we first identified a T-DNA insertion mutation in the single FtsZ1 gene in Arabidopsis thaliana, AtFtsZ1-1.

ARC5, a cytosolic dynamin-like protein from plants, is part of the chloroplast division machinery.

Chloroplast division in plant cells is orchestrated by a complex macromolecular machine with components positioned on both the inner and outer envelope surfaces. The only plastid division proteins identified to date are of endosymbiotic origin and are localized inside the organelle. Employing positional cloning methods in Arabidopsis in conjunction with a novel strategy for pinpointing the mutant locus, we have identified a gene encoding a new chloroplast division protein, ARC5.