The OPR Protein MTHI1 Controls the Expression of Two Different Subunits of ATP Synthase CFo in Chlamydomonas reinhardtii

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Ozawa, Shin-Ichiro | Cavaiuolo, Marina | Jarrige, Domitille | Kuras, Richard | Rutgers, Mark | Eberhard, Stephan | Drapier, Dominique | Wollman, Francis-André | Choquet, Yves

Edité par CCSD ; American Society of Plant Biologists (ASPB) -

International audience. One sentence summary: The OPR protein MTHI1 is a major actor in the biogenesis of chloroplast ATP synthase that co-regulates the expression of AtpH and AtpI, the two subunits of the proton channel in green algae. ABSTRACT In the green alga Chlamydomonas reinhardtii, chloroplast gene expression is tightly regulated post-transcriptionally by gene-specific transacting protein factors. Here we report the identification of the octotricopeptide repeat (OPR) protein MTHI1, which is critical for the biogenesis of chloroplast ATP synthase CFo. Unlike most transacting factors characterised so far in C. reinhardtii, which control the expression of a single gene, MTHI1 targets two distinct transcripts: it is required for the accumulation and translation of atpH mRNA, encoding a subunit of the selective proton channel, but it also enhances the translation of atpI mRNA, which encodes the other subunit of the channel. MTHI1 targets the 5'UTRs of both the atpH and atpI genes. Co-immuno-precipitation and small RNA sequencing revealed that MTHI1 binds specifically a sequence highly conserved among Chlorophyceae and the Ulvale clade of Ulvophyceae at the 5'end of tri-phosphorylated atpH mRNA. A very similar sequence, located approximately 60 nt upstream of the atpI initiation codon, was also found in some Chlorophyceae and Ulvale algae species and is essential for atpI mRNA translation in C. reinhardtii. Such a dual targeted transacting factor provides a means to co-regulate the expression of the two proton hemi-channels.

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