Mitochondrial transcription termination factors (mTERFs) are highly conserved proteins in metazoans. Plants have many more mTERF proteins than animals. The functions and the underlying mechanisms of plants’ mTERFs remain largely unknown. In plants, mTERF family proteins are present in both mitochondria and plastids and are involved in gene expression in these organelles through different mechanisms. In this study, we screened Arabidopsis mutants with pigment-defective phenotypes and isolated a T-DNA insertion mutant exhibiting seedling-lethal and albino phenotypes [seedling lethal 1 (sl1)]. The SL1 gene encodes an mTERF protein localized in the chloroplast stroma. The sl1 mutant showed severe defects in chloroplast development, photosystem assembly, and the accumulation of photosynthetic proteins. Furthermore, the transcript levels of some plastid-encoded proteins were significantly reduced in the mutant, suggesting that SL1/mTERF3 may function in the chloroplast gene expression. Indeed, SL1/mTERF3 interacted with PAP12/PTAC7, PAP5/PTAC12, and PAP7/PTAC14 in the subgroup of DNA/RNA metabolism in the plastid-encoded RNA polymerase (PEP) complex. Taken together, the characterization of the plant chloroplast mTERF protein, SL1/mTERF3, that associated with PEP complex proteins provided new insights into RNA transcription in the chloroplast.
The maintenance of a proton gradient across the thylakoid membrane is an integral aspect of photosynthesis that is mainly established by the splitting of water molecules in photosystem II and plastoquinol oxidation at the cytochrome complex, and it is necessary for the generation of ATP in the last step of photophosphorylation. Although environmental stresses, such as high temperatures, are known to disrupt this fundamental process, only a few studies have explored the molecular mechanisms underlying proton gradient regulation during stress. The present study identified a heat‐sensitive mutant that displays aberrant photosynthesis at high temperatures. This mutation was mapped to AtFtsH11, which encodes an ATP‐dependent AAA‐family metalloprotease. We showed that AtFtsH11 localizes to the chloroplast inner envelope membrane and is capable of degrading the ATP synthase assembly factor BFA3 under heat stress. We posit that this function limits the amount of ATP synthase integrated into the thylakoid membrane to regulate proton efflux from the lumen to the stroma. Our data also suggest that AtFtsH11 is critical in stabilizing photosystem II and cytochrome complexes at high temperatures, and additional studies can further elucidate the specific molecular functions of this critical regulator of photosynthetic thermotolerance.
DNA methylation plays an important role in regulating plant development, including organ and tissue differentiation, which may determine variations in agronomic traits. However, no reports exist for the regulation of leaf colour in wheat. The present study investigated the chloroplast structure and epigenetic mechanisms regulating leaf colour in an albino mutant of wheat (Triticum aestivum L.) cv. Xinong 1376. Structural analysis was performed by scanning and transmission electron microscopy, and epigenetic modifications were detected by methylation-sensitive amplification polymorphism (MSAP) analysis. Mesophyll cells of green leaves showed a well-ordered arrangement and they were filled with chloroplasts with intact lamellar structures and thylakoid membranes. By contrast, mesophyll cells of red and white leaves were disorganised and contained only a few plastids or chloroplasts with no lamellar structures or thylakoid membranes. Comparison of MSAP profiles revealed that white or red leaves had higher levels of cytosine methylation and showed changes in polymorphic loci compared with green leaves (4.35% and 4.10%, respectively). We sequenced 150 DNA fragments that were differentially displayed in MSAP patterns of white or red and green leaves of the Xinong 1376 albino mutant. A further BLAST search of 77 cloned sequences located them in coding regions. Most of these sequences were found to be involved in processes such as signal transduction, transcription regulation, post-transcriptional processing, DNA modification and repair, transport, biosynthesis of cellulose, photosynthesis, protein ubiquitination, stress responses, and retroposition. Expression analysis demonstrated a decrease in the transcription of two methylated genes, psaA and psbD, which are involved in the photosystem. Although the DNA methylation changes and leaf colour changes were not directly associated, these results may indicate that methylation of specific genes is an active and rapid epigenetic response to variation of leaf colour in the Xinong 1376 albino mutant, further elucidating the mechanism of variation in leaf colour.
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