HIGH CHLOROPHYLL FLUORESCENCE145 Binds to and Stabilizes the psaA 5′ UTR via a Newly Defined Repeat Motif in Embryophyta

Abstract

ORCID IDs: 0000-0003-2740-5991 (N.M.); 0000-0003-2973-9514 (J.M.)The seedling-lethal Arabidopsis thaliana high chlorophyll fluorescence145 (hcf145) mutation leads to reduced stability of the plastid tricistronic psaA-psaB-rps14 mRNA and photosystem I (PSI) deficiency. Here, we genetically mapped the HCF145 gene, which encodes a plant-specific, chloroplast-localized, modular protein containing two homologous domains related to the polyketide cyclase family comprising 37 annotated Arabidopsis proteins of unknown function. Two further highly conserved and previously uncharacterized tandem repeat motifs at the C terminus, herein designated the transcript binding motif repeat (TMR) domains, confer sequence-specific RNA binding capability to HCF145. Homologous TMR motifs are often found as multiple repeats in quite diverse proteins of green and red algae and in the cyanobacterium Microcoleus sp PCC 7113 with unknown function. HCF145 represents the only TMR protein found in vascular plants. Detailed analysis of hcf145 mutants in Arabidopsis and Physcomitrella patens as well as in vivo and in vitro RNA binding assays indicate that HCF145 has been recruited in embryophyta for the stabilization of the psaA-psaB-rps14 mRNA via specific binding to its 59 untranslated region. The polyketide cyclase-related motifs support association of the TMRs to the psaA RNA, presumably pointing to a regulatory role in adjusting PSI levels according to the requirements of the plant cell.

A Nitrogen-Fixing Subunit Essential for Accumulating 4Fe-4S-Containing Photosystem I Core Proteins

“…In addition, subchloroplast fractionation and subsequent immunoblot analysis showed that NFU1 and NFU2 are located in the chloroplast stroma (Yabe et al, 2004). The three plastidtargeted NFU proteins contain an N-terminal redoxactive NFU domain with the conserved CXXC motif and a C-terminal redox-inactive NFU domain; the two mitochondrion-targeted NFU proteins contain an N-terminal domain that is unique to nonplastid types of eukaryotic NFU proteins and a C-terminal redoxactive NFU domain with the conserved CXXC motif (Gao et al, 2013;Manavski et al, 2015). Immunoblot analysis showed that the three plastid-targeted NFU proteins exhibited different expression patterns: NFU1 is expressed at a very low level; NFU2 is expressed ubiquitously in all the tissues tested, including roots, true rosette leaves, cauline leaves, flower stalks, and flowers; and NFU3 is expressed predominantly in the aerial portion of the plants (Yabe et al, 2004).…”

PUMPKIN, the Sole Plastid UMP Kinase, Associates with Group II Introns and Alters Their Metabolism

“…Our first reason was the lack of complementation experiments and RNA-binding studies as well as enzymatic tests of DPT1. Second, with HCF145, a factor required for psaA/psaB/rps14 RNA accumulation had already been unambiguously identified (Manavski et al, 2015). Indeed, genotyping experiments in two different laboratories (Jörg Meurer and Torsten Möhlmann) failed to confirm the described T-DNA insertion into the At3g18680 (N829192) locus.…”

“…RNA-gel-blot analyses, total RNA isolation, electrophoresis, blotting, and hybridization with radioactive labeled probes were carried out as described by Manavski et al (2015). Oligonucleotides and primers for PCR-probes are listed in Supplemental Table S1.…”

“…Under oxidizing conditions, the RNA-binding N terminus of the large Rubisco subunit becomes exposed and binds RNAs for regulation of translation, thus connecting the redox status with plastid gene expression (Yosef et al, 2004;Cohen et al, 2006). Likewise, predicted binding domains of the HCF145 protein for secondary metabolites were shown to impact RNA-binding affinity important for stabilization of the psaA/psaB/rps14 mRNA and accumulation of PSI, suggesting a metabolic control of psaA/psaB/rps14 gene expression (Lezhneva and Meurer, 2004;Manavski et al, 2015).…”

Chlorophyll Fluorescence Video Imaging: A Versatile Tool for Identifying Factors Related to Photosynthesis

“…Following its application for screening of Chlamydomonas mutant libraries (see for example Harris, 1989 ) the concept was tested in higher plants ( Miles and Daniel, 1973 ) and employed for the screening of maize ( Miles and Daniel, 1974 ; Barkan et al, 1986 ; Taylor et al, 1987 ) and Arabidopsis mutant libraries ( Dinkins et al, 1994 ; Meurer et al, 1996b ). Several factors involved in chloroplast biogenesis were identified using the hcf phenotyping method, including the maize proteins HCF106, HCF60, and HCF136 (reviewed in: Belcher et al, 2015 ) and the Arabidopsis proteins HCF5 ( Dinkins et al, 1997 ), HCF101 ( Lezhneva et al, 2004 ), HCF107 ( Felder et al, 2001 ), HCF109 ( Meurer et al, 1996a ), HCF145 ( Lezhneva and Meurer, 2004 ; Manavski et al, 2015 ), HCF152 ( Meierhoff et al, 2003 ) and LPA1 ( Peng et al, 2006 ).…”