FtsH4 protease controls biogenesis of the PSII complex by dual regulation of high light-inducible proteins

Genome-wide analysis of filamentous temperature-sensitive H protease (ftsH) gene family in soybean

BACKGROUND

The filamentous temperature-sensitive H protease (ftsH) gene family belongs to the ATP-dependent zinc metalloproteins, and ftsH genes play critical roles in plant chloroplast development and photosynthesis.

RESULTS

In this study, we performed genome-wide identification and a systematic analysis of soybean ftsH genes. A total of 18 GmftsH genes were identified. The subcellular localization was predicted to be mainly in cell membranes and chloroplasts, and the gene structures, conserved motifs, evolutionary relationships, and expression patterns were comprehensively analyzed. Phylogenetic analysis of the ftsH gene family from soybean and various other species revealed six distinct clades, all of which showed a close relationship to Arabidopsis thaliana. The members of the GmftsH gene family were distributed on 13 soybean chromosomes, with intron numbers ranging from 3 to 15, 13 pairs of repetitive segment. The covariance between these genes and related genes in different species of Oryza sativa, Zea mays, and Arabidopsis thaliana was further investigated. The transcript expression data revealed that the genes of this family showed different expression patterns in three parts, the root, stem, and leaf, and most of the genes were highly expressed in the leaves of the soybean plants. Fluorescence-based real-time quantitative PCR (qRT-PCR) showed that the expression level of GmftsH genes varied under different stress treatments. Specifically, the genes within this family exhibited various induction levels in response to stress conditions of 4℃, 20% PEG-6000, and 100 mmol/L NaCl. These findings suggest that the GmftsH gene family may play a crucial role in the abiotic stress response in soybeans. It was also found that the GmftsH7 gene was localized on the cell membrane, and its expression was significantly upregulated under 4 ℃ treatment. In summary, by conducting a genome-wide analysis of the GmftsH gene family, a strong theoretical basis is established for future studies on the functionality of GmftsH genes.

CONCLUSIONS

This research can potentially serve as a guide for enhancing the stress tolerance characteristics of soybean.

Bacteria can anticipate the seasons: photoperiodism in cyanobacteria

Photoperiodic Time Measurement is the ability of plants and animals to measure differences in day/night-length (photoperiod) and use that information to anticipate critical seasonal transformations such as annual temperature cycles. This timekeeping phenomenon triggers adaptive responses in higher organisms such as gonadal growth/regression, flowering, and hibernation. Unexpectedly, we discovered this capability in cyanobacteria, unicellular prokaryotes with generation times of only 5-6 h. Cyanobacteria in short winter-like days develop enhanced resistance to cold that involves desaturation of membrane lipids and differential programs of gene transcription, including stress response pathways. As in eukaryotes, this photoperiodic timekeeping requires an intact circadian clockwork and develops over multiple cycles. Therefore, photoperiodic timekeeping evolved in much simpler organisms than previously appreciated, and involved genetic responses to stresses that recur seasonally.

The cyanobacterial FtsH4 protease controls accumulation of protein factors involved in the biogenesis of photosystem I

Membrane-bound FtsH proteases are universally present in prokaryotes and in mitochondria and chloroplasts of eukaryotic cells. These metalloproteases are often critical for viability and play both protease and chaperone roles to maintain cellular homeostasis. In contrast to most bacteria bearing a single ftsH gene, cyanobacteria typically possess four FtsH proteases (FtsH1-4) forming heteromeric (FtsH1/3 and FtsH2/3) and homomeric (FtsH4) complexes. The functions and substrate repertoire of each complex are however poorly understood. To identify substrates of the FtsH4 protease complex we established a trapping assay in the cyanobacterium Synechocystis PCC 6803 utilizing a proteolytically inactivated trapFtsH4-His. Around 40 proteins were specifically enriched in trapFtsH4 pulldown when compared with the active FtsH4. As the list of putative FtsH4 substrates contained Ycf4 and Ycf37 assembly factors of Photosystem I (PSI), its core PsaB subunit and the IsiA chlorophyll-binding protein that associates with PSI during iron stress, we focused on these PSI-related proteins. Therefore, we analysed their degradation by FtsH4 in vivo in Synechocystis mutants and in vitro using purified substrates. The data confirmed that FtsH4 degrades Ycf4, Ycf37, IsiA, and also the individual PsaA and PsaB subunits in the unassembled state but not when assembled within the PSI complexes. A possible role of FtsH4 in the PSI life-cycle is discussed.

Halotolerance mechanisms in salt‑tolerant cyanobacteria

Cyanobacteria are ubiquitously distributed in nature and are the most abundant photoautotrophs on Earth. Their long evolutionary history reveals that cyanobacteria have a remarkable capacity and strong adaptive tendencies to thrive in a variety of conditions. Thus, they can survive successfully, especially in harsh environmental conditions such as salty environments, high radiation, or extreme temperatures. Among others, salt stress because of excessive salt accumulation in salty environments, is the most common abiotic stress in nature and hampers agricultural growth and productivity worldwide. These detrimental effects point to the importance of understanding the molecular mechanisms underlying the salt stress response. While it is generally accepted that the stress response mechanism is a complex network, fewer efforts have been made to represent it as a network. Substantial evidence revealed that salt-tolerant cyanobacteria have evolved genomic specific mechanisms and high adaptability in response to environmental changes. For example, extended gene families and/or clusters of genes encoding proteins involved in the adaptation to high salinity have been collectively reported. This chapter focuses on recent advances and provides an overview of the molecular basis of halotolerance mechanisms in salt‑tolerant cyanobacteria as well as multiple regulatory pathways. We elaborate on the major protective mechanisms, molecular mechanisms associated with halotolerance, and the global transcriptional landscape to provide a gateway to uncover gene regulation principles. Both knowledge and omics approaches are utilized in this chapter to decipher the mechanistic insights into halotolerance. Collectively, this chapter would have a profound impact on providing a comprehensive understanding of halotolerance in salt‑tolerant cyanobacteria.

Regulation of chloroplast protein degradation

Chloroplasts are unique organelles that not only provide sites for photosynthesis and many metabolic processes, but also are sensitive to various environmental stresses. Chloroplast proteins are encoded by genes from both nuclear and chloroplast genomes. During chloroplast development and responses to stresses, the robust protein quality control systems are essential for regulation of protein homeostasis and the integrity of chloroplast proteome. In this review, we summarize the regulatory mechanisms of chloroplast protein degradation refer to protease system, ubiquitin-proteasome system, and the chloroplast autophagy. These mechanisms symbiotically play a vital role in chloroplast development and photosynthesis under both normal or stress conditions.