The Atypical Short-Chain Dehydrogenases HCF173 and HCF244 Are Jointly Involved in Translational Initiation of the psbA mRNA of Arabidopsis  

Abstract

The related proteins D1 and D2 together build up the photosystem II reaction center. Synthesis of D1 (PsbA) is highly regulated in all photosynthetic organisms. The mechanisms and specific protein factors involved in controlled expression of the psbA gene in higher plants are highly elusive. Here, we report on the identification of a chloroplast-located protein, HCF244 (for high chlorophyll fluorescence244), which is essentially required for translational initiation of the psbA messenger RNA in Arabidopsis (Arabidopsis thaliana). The factor is highly conserved between land plants, algae, and cyanobacteria. HCF244 was identified by coexpression analysis of HCF173, which encodes a protein that is also necessary for psbA translational initiation and in addition for stabilization of this messenger RNA. Phenotypic characterization of the mutants hcf244 and hcf173 suggests that the corresponding proteins operate cooperatively during psbA translation. Immunolocalization studies detected the majority of the two proteins at the thylakoid membrane. Both HCF244 and HCF173 are members of the atypical short-chain dehydrogenase/reductase superfamily, a modified group, which has lost enzyme activity but acquires new functions in the metabolism of the cell.

Thylakoid proteome modulation in pea plants grown at different irradiances: quantitative proteomic profiling in a non‐model organism aided by transcriptomic data integration

“…HCF136, HHL1, MPH2, PPL1 and Psb27) accumulated upon HL acclimation; notably, the amount of HCF244, LPA1 and MET1 was already increased in ML (Figure ). From the literature it is established that HCF244 is involved in translation of psbA (Link et al ., ), LPA1 is involved in insertion of PsbA during PSII reassembly (Zhang et al ., ) and MET1 interacts with the PsbB/PsbC intermediates of PSII assembly (Bhuiyan et al ., ). Considering the similar rate of accumulation of these proteins in ML, we propose their direct and concerted involvement in turnover of PsbA, which is already enhanced at moderate irradiances (Aro et al ., ).…”

Discovery of a Chlorophyll Binding Protein Complex Involved in the Early Steps of Photosystem II Assembly in Synechocystis

“…Link et al (2012) have pointed out that this motif could in fact bind RNA instead of being involved in redox reactions typical for the family of atypical short-chain dehydrogenases/reductases to which Ycf39 can be assigned (Kavanagh et al, 2008). As RNAs are components of ribosomes, the motif might represent a binding site for ribosomes or possibly for mRNA.…”

“…Genes for one-helix-proteins (Ohps) homologous to Hlips have been identified in the Arabidopsis genome (Engelken et al, 2010) and like Hlips are also induced by high irradiance (Jansson et al, 2000;Andersson et al, 2003). The Ycf39 homolog from Arabidopsis called High Chlorophyll Fluorescence 244 (HCF244) (Link et al, 2012) is essential for normal accumulation of PSII and the protein has been shown to be needed for biosynthesis of the D1 protein, although the mechanism of its action has not been explained. Our data are in accordance with the close relationship between Ycf39 and biosynthesis of the D1 protein.…”

A Cyanobacterial Chlorophyll Synthase-HliD Complex Associates with the Ycf39 Protein and the YidC/Alb3 Insertase

“…This observation led to speculation that Ycf39 is a chaperone-like protein involved in quinone insertion into the PSII complex (Ermakova-Gerdes and Vermaas, 1999). Inactivation of the Arabidopsis Ycf39 homolog Hcf244 greatly decreased accumulation of PSII core proteins, and although the mechanism of Hcf244 action was not explained, it appears to be connected to the synthesis of the D1 protein (Link et al, 2012). The association of the cyanobacterial Ycf39 with ChlG and HliD suggests its role in pigment insertion or modification.…”