Cell Growth Defect Factor1/CHAPERONE-LIKE PROTEIN OF POR1 Plays a Role in Stabilization of Light-Dependent Protochlorophyllide Oxidoreductase in Nicotiana benthamiana and Arabidopsis    

Abstract

Angiosperms require light for chlorophyll biosynthesis because one reaction in the pathway, the reduction of protochlorophyllide (Pchlide) to chlorophyllide, is catalyzed by the light-dependent protochlorophyllide oxidoreductase (POR). Here, we report that Cell growth defect factor1 (Cdf1), renamed here as CHAPERONE-LIKE PROTEIN OF POR1 (CPP1), an essential protein for chloroplast development, plays a role in the regulation of POR stability and function. Cdf1/CPP1 contains a J-like domain and three transmembrane domains, is localized in the thylakoid and envelope membranes, and interacts with POR isoforms in chloroplasts. CPP1 can stabilize POR proteins with its holdase chaperone activity. CPP1 deficiency results in diminished POR protein accumulation and defective chlorophyll synthesis, leading to photobleaching and growth inhibition of plants under light conditions. CPP1 depletion also causes reduced POR accumulation in etioplasts of dark-grown plants and as a result impairs the formation of prolamellar bodies, which subsequently affects chloroplast biogenesis upon illumination. Furthermore, in cyanobacteria, the CPP1 homolog critically regulates POR accumulation and chlorophyll synthesis under high-light conditions, in which the dark-operative Pchlide oxidoreductase is repressed by its oxygen sensitivity. These findings and the ubiquitous presence of CPP1 in oxygenic photosynthetic organisms suggest the conserved nature of CPP1 function in the regulation of POR.

Cell growth defect factor 1 is crucial for the plastid import of NADPH:protochlorophyllide oxidoreductase A in Arabidopsis thaliana

“…Seeds of the Atcdf1 mutant GK-852F12-025757 were obtained from GABI-Kat (www.gabi-kat.de) but did not provide viable plants, consistent with previous results (20,23). To study the impact of CDF1 deficiency in vivo, we therefore used DEX-inducible RNAi, as described by Lee et al (23).…”

“…CDF1 proteins have no reported homology with any known animal protein, except for the presence of a J-like domain characteristic of DnaJ/Hsp40-type cochaperones (21,22). Hydrophobicity analyses revealed that CDF1 and the protein encoded by At3g51140 contain three trans-membrane domains, whereas other CDF1-related proteins, including Synechocystis slr1918 and At2g20920, possess four trans-membrane domains (19,20,23). …”

“…Attempts to isolate homozygous knockout plants from public mutant collections (GK-852F12-025757; GABI-Kat) failed because of the lethality of the mutation (20,23). We therefore examined in vivo effects of CDF1 deficiency in Arabidopsis by using the dexamethasone (DEX)-inducible RNA interference (RNAi) approach developed by Lee et al (23).…”

“…Attempts to isolate homozygous knockout plants from public mutant collections (GK-852F12-025757; GABI-Kat) failed because of the lethality of the mutation (20,23). We therefore examined in vivo effects of CDF1 deficiency in Arabidopsis by using the dexamethasone (DEX)-inducible RNA interference (RNAi) approach developed by Lee et al (23). DEX-inducible AtCdf1 RNAi Arabidopsis plants were cultivated on agar plates supplemented with DEX added right from the beginning of seed germination and kept either in continuous white light (photomorphogenesis) or darkness (skotomorphogenesis) (Fig.…”

“…Etioplasts were isolated from 4.5-d-old dark-grown plants that had been pretreated with DEX 12 h before seedling harvest and thus did not express any CDF1 protein (23) (Fig. S3).…”