Essays in Biochemistry

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ISSN / EISSN : 0071-1365 / 1744-1358
Published by: Portland Press Ltd. (10.1042)
Total articles ≅ 910
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Jian Chen, Xiaoxiao Zhang, John P. Rathjen,
Published: 22 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210072

Abstract:
Plants deploy extracellular and intracellular immune receptors to sense and restrict pathogen attacks. Rapidly evolving pathogen effectors play crucial roles in suppressing plant immunity but are also monitored by intracellular nucleotide-binding, leucine-rich repeat immune receptors (NLRs), leading to effector-triggered immunity (ETI). Here, we review how NLRs recognize effectors with a focus on direct interactions and summarize recent research findings on the signalling functions of NLRs. Coiled-coil (CC)-type NLR proteins execute immune responses by oligomerizing to form membrane-penetrating ion channels after effector recognition. Some CC-NLRs function in sensor–helper networks with the sensor NLR triggering oligomerization of the helper NLR. Toll/interleukin-1 receptor (TIR)-type NLR proteins possess catalytic activities that are activated upon effector recognition-induced oligomerization. Small molecules produced by TIR activity are detected by additional signalling partners of the EDS1 lipase-like family (enhanced disease susceptibility 1), leading to activation of helper NLRs that trigger the defense response.
Niels Aerts, Himanshu Chhillar, ,
Published: 21 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210100

Abstract:
Transcriptional reprogramming is an integral part of plant immunity. Tight regulation of the immune transcriptome is essential for a proper response of plants to different types of pathogens. Consequently, transcriptional regulators are proven targets of pathogens to enhance their virulence. The plant immune transcriptome is regulated by many different, interconnected mechanisms that can determine the rate at which genes are transcribed. These include intracellular calcium signaling, modulation of the redox state, post-translational modifications of transcriptional regulators, histone modifications, DNA methylation, modulation of RNA polymerases, alternative transcription inititation, the Mediator complex and regulation by non-coding RNAs. In addition, on their journey from transcription to translation, mRNAs are further modulated through mechanisms such as nuclear RNA retention, storage of mRNA in stress granules and P-bodies, and post-transcriptional gene silencing. In this review, we highlight the latest insights into these mechanisms. Furthermore, we discuss some emerging technologies that promise to greatly enhance our understanding of the regulation of the plant immune transcriptome in the future.
Jessica Erickson, Philipp Weckwerth, ,
Published: 20 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210088

Abstract:
Plant immunity is crucial to plant health but comes at an expense. For optimal plant growth, tight immune regulation is required to prevent unnecessary rechannelling of valuable resources. Pattern- and effector-triggered immunity (PTI/ETI) represent the two tiers of immunity initiated after sensing microbial patterns at the cell surface or pathogen effectors secreted into plant cells, respectively. Recent evidence of PTI-ETI cross-potentiation suggests a close interplay of signalling pathways and defense responses downstream of perception that is still poorly understood. This review will focus on controls on plant immunity through phosphorylation, a universal and key cellular regulatory mechanism. Rather than a complete overview, we highlight “what’s new in protein kinase/phosphatase signalling” in the immunity field. In addition to phosphoregulation of components in the pattern recognition receptor (PRR) complex, we will cover the actions of the major immunity-relevant intracellular protein kinases/phosphatases in the ‘signal relay’, namely calcium-regulated kinases (e.g. calcium-dependent protein kinases, CDPKs), mitogen-activated protein kinases (MAPKs), and various protein phosphatases. We discuss how these factors define a phosphocode that generates cellular decision-making ‘logic gates’, which contribute to signalling fidelity, amplitude, and duration. To underscore the importance of phosphorylation, we summarize strategies employed by pathogens to subvert plant immune phosphopathways. In view of recent game-changing discoveries of ETI-derived resistosomes organizing into calcium-permeable pores, we speculate on a possible calcium-regulated phosphocode as the mechanistic control of the PTI-ETI continuum.
Bei Wang,
Published: 17 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20220009

Abstract:
Cancer stem cells (CSCs) are a subpopulation of tumor cells with self-renewal ability. Increasing evidence points to the critical roles of CSCs in tumorigenesis, metastasis, therapy resistance, and cancer relapse. As such, the elimination of CSCs improves cancer treatment outcomes. However, challenges remain due to limited understanding of the molecular mechanisms governing self-renewal and survival of CSCs. Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 screening has been increasingly used to identify genetic determinants in cancers. In this primer, we discuss the progress made and emerging opportunities of coupling advanced CRISPR screening systems with CSC models to reveal the understudied vulnerabilities of CSCs.
Published: 15 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210070

Abstract:
Plants must cope with an ever-changing environment, including concurrent biotic and abiotic stresses. The ubiquitin–proteasome system (UPS) is intricately involved in regulating signaling events that facilitate cellular changes required to mitigate the detrimental effects of environmental stress. A key component of the UPS are ubiquitin ligases (or E3s) that catalyze the attachment of ubiquitin molecules to select substrate proteins, which are then recognized by the 26S proteasome for degradation. With the identification of substrate proteins, a growing number of E3s are shown to differentially regulate responses to abiotic as well as bioitic stresses. The review discusses select E3s to illustrate the role of ubiquitin ligases as negative and/or positive regulators of responses to both biotic and abiotic stresses.
Shiji Hou,
Published: 14 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210090

Abstract:
The phytohormones salicylic acid (SA) and jasmonic acid (JA) are major players in plant immunity. Numerous studies have provided evidence that SA- and JA-mediated signaling interact with each other (SA-JA crosstalk) to orchestrate plant immune responses against pathogens. At the same time, SA-JA crosstalk is often exploited by pathogens to promote their virulence. In this review, we summarize our current knowledge of molecular mechanisms for and modulations of SA-JA crosstalk during pathogen infection.
Published: 9 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210060

Abstract:
Proper regulation of protein homeostasis (proteostasis) is essential for all organisms to survive. A diverse range of post-translational modifications (PTMs) allow precise control of protein abundance, function and cellular localisation. In eukaryotic cells, ubiquitination is a widespread, essential PTM that regulates most, if not all cellular processes. Ubiquitin is added to target proteins via a well-defined enzymatic cascade involving a range of conjugating enzymes and ligases, while its removal is catalysed by a class of enzymes known as deubiquitinases (DUBs). Many human diseases have now been linked to DUB dysfunction, demonstrating the importance of these enzymes in maintaining cellular function. These findings have led to a recent explosion in studying the structure, molecular mechanisms and physiology of DUBs in mammalian systems. Plant DUBs have however remained relatively understudied, with many DUBs identified but their substrates, binding partners and the cellular pathways they regulate only now beginning to emerge. This review focuses on the most recent findings in plant DUB biology, particularly on newly identified DUB substrates and how these offer clues to the wide-ranging roles that DUBs play in the cell. Furthermore, the future outlook on how new technologies in mammalian systems can accelerate the plant DUB field forward is discussed.
, Lamia Aouini, Yajun Wang,
Published: 7 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210081

Abstract:
Plant immunity is triggered following the perception of pathogen-derived molecules by plant receptor proteins. Two protein families, membrane-localized receptor-like kinases (RLK) and intracellular nucleotide-binding leucine-rich repeat (NLR) receptors, play key roles in pathogen perception and in the initiation of downstream signaling cascades that lead to defense responses. In addition to RLKs and NLRs, recent research has identified additional protein families that function as plant resistance (R) proteins. In particular, the botanical tribe Triticeae, which includes the globally important crop species wheat and barley, has played a significant role in the discovery of ‘unconventional’ R proteins. In this review, we will summarize the current knowledge on unconventional R genes in Triticeae and the proteins they encode. The knowledge on unconventional R proteins will not only broaden our understanding of plant–pathogen interactions but also have great implications for disease resistance breeding in crops.
Qian Yan, Xiaona Fang, Chenxi Li, Ping Lan,
Published: 7 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20220025

Abstract:
Cancer stem cells (CSCs) are considered as a small population of cells with stem-like properties within the tumor bulk, and are largely responsible for tumor recurrence, metastasis, and therapy resistance. CSCs share critical features with embryonic stem cells (ESCs). The pluripotent transcription factors (TFs) and developmental signaling pathways of ESCs are invariably hijacked by CSCs termed ‘oncofetal drivers’ in many cancers, which are rarely detectable in adult tissues. The unique expression pattern makes oncofetal proteins ideal therapeutic targets in cancer treatment. Therefore, elucidation of oncofetal drivers in cancers is critical for the development of effective CSCs-directed therapy. In this review, we summarize the common pluripotent TFs such as OCT4, SOX2, NANOG, KLF4, MYC, SALL4, and FOXM1, as well as the development signaling including Wnt/β-catenin, Hedgehog (Hh), Hippo, Notch, and TGF-β pathways of ESCs and CSCs. We also describe the newly identified oncofetal proteins that drive the self-renewal, plasticity, and therapy-resistance of CSCs. Finally, we explore how the clinical implementation of targeting oncofetal drivers, including small-molecule inhibitors, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) can facilitate the development of CSCs-directed therapy.
Published: 7 June 2022
Essays in Biochemistry; https://doi.org/10.1042/ebc20210058

Abstract:
Several protein homeostasis (proteostasis) pathways safeguard the integrity of thousands of proteins that localize in plant chloroplasts, the indispensable organelles that perform photosynthesis, produce metabolites, and sense environmental stimuli. In this review, we discuss the latest efforts directed to define the molecular process by which proteins are imported and sorted into the chloroplast. Moreover, we describe the recently elucidated protein folding and degradation pathways that modulate the levels and activities of chloroplast proteins. We also discuss the links between the accumulation of misfolded proteins and the activation of signalling pathways that cope with folding stress within the organelle. Finally, we propose new research directions that would help to elucidate novel molecular mechanisms to maintain chloroplast proteostasis.
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