title: The N-terminal domain of chlorophyllide a oxygenase confers protein instability in response to chlorophyll B accumulation in Arabidopsis.
abstract: Plants acclimate to variations in light intensity by changing the antenna size of photosystems. This acclimation allows them to undergo efficient photosynthesis and creates a protective strategy to minimize photodamage. Chlorophyll b synthesis by chlorophyllide a oxygenase (CAO) is a key regulatory step in the control of antenna size. Recently, we found that higher plant CAOs consist of three domains (A, B, and C domains) and confirmed that the C domain possesses catalytic function. To investigate the function of the A domain, we fused various combinations of these three domains with green fluorescent protein (GFP) and introduced them into Arabidopsis thaliana. When a full-length CAO-GFP fusion protein was introduced into a chlorophyll b-less chlorina1-1 mutant, chlorophyll b accumulated to almost the same levels as in the chlorophyll b-containing Columbia wild type, but the CAO-GFP could not be detected by immunoblotting. By contrast, when a GFP-C domain fusion was introduced into chlorina1-1 or Columbia wild type, a large amount of GFP-C domain protein accumulated and the chlorophyll a/b ratio decreased drastically from 3.6 to 2.2 in Columbia wild type. When an A domain-GFP was introduced into Columbia wild type, A domain-GFP levels were very low. Conversely, a large amount of the protein accumulated when it was introduced into the chlorina1-1 mutant. These results indicate that the A domain may sense the presence of chlorophyll b and regulate the accumulation of CAO protein in the chloroplasts.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yamasato
authors.forename: Nozomi
authors.initials: N
authors.lastname: Nagata
authors.forename: Ryouichi
authors.initials: R
authors.lastname: Tanaka
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism*; D025461:Feedback, Physiological / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000378:metabolism; D009154:Mutation / Q000502:physiology; D010105:Oxygenases / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; C037184:chlorophyll b; D010105:Oxygenases; C115272:chlorophyll a oxygenase