Metabolic Alterations in the Enoyl-CoA Hydratase 2 Mutant Disrupt Peroxisomal Pathways in Seedlings

Genome-wide expression analysis of LACS gene family implies GhLACS25 functional responding to salt stress in cotton

BACKGROUND

Long-chain acyl-coenzyme A synthetase (LACS) is a type of acylating enzyme with AMP-binding, playing an important role in the growth, development, and stress response processes of plants.

RESULTS

The research team identified different numbers of LACS in four cotton species (Gossypium hirsutum, Gossypium barbadense, Gossypium raimondii, and Gossypium arboreum). By analyzing the structure and evolutionary characteristics of the LACS, the GhLACS were divided into six subgroups, and a chromosome distribution map of the family members was drawn, providing a basis for further research classification and positioning. Promoter cis-acting element analysis showed that most GhLACS contain plant hormones (GA, MeJA) or non-biological stress-related cis-elements. The expression patterns of GhLACS under salt stress treatment were analyzed, and the results showed that GhLACS may significantly participate in salt stress response through different mechanisms. The research team selected 12 GhLACSs responsive to salt stress for tissue expression analysis and found that these genes are expressed in different tissues.

CONCLUSIONS

There is a certain diversity of LACS among different cotton species. Analysis of promoter cis-acting elements suggests that GhLACS may be involved in regulating plant growth, development and stress response processes. GhLACS25 was selected for in-depth study, which confirmed its significant role in salt stress response through virus-induced gene silencing (VIGS) and induced expression in yeast cells.

Direct balancing of lipid mobilization and reactive oxygen species production by the epoxidation of fatty acid catalyzed by a cytochrome P450 protein during seed germination

Fatty acid (FA) β-oxidation provides energy for oil seed germination but also produces massive byproduct reactive oxygen species (ROS), posing potential oxidative damage to plant cells. How plants overcome the contradiction between energy supply and ROS production during seed germination remains unclear. In this study, we identified an Arabidopsis mvs1 (methylviologen-sensitive) mutant that was hypersensitive to ROS and caused by a missense mutation (G1349 substituted as A) of a cytochrome P450 gene, CYP77A4. CYP77A4 was highly expressed in germinating seedling cotyledons, and its protein is localized in the endoplasmic reticulum. As CYP77A4 catalyzes the epoxidation of unsaturated FA, disruption of CYP77A4 resulted in increased unsaturated FA abundance and over accumulated ROS in the mvs1 mutant. Consistently, scavenging excess ROS or blocking FA β-oxidation could repress the ROS overaccumulation and hypersensitivity in the mvs1 mutant. Furthermore, H₂ O₂ transcriptionally upregulated CYP77A4 expression and post-translationally modified CYP77A4 by sulfenylating its Cysteine-456, which is necessary for CYP77A4's role in modulating FA abundance and ROS production. Together, our study illustrates that CYP77A4 mediates direct balancing of lipid mobilization and ROS production by the epoxidation of FA during seed germination.

Leaf-size control beyond transcription factors: Compensatory mechanisms

Plant leaves display abundant morphological richness yet grow to characteristic sizes and shapes. Beginning with a small number of undifferentiated founder cells, leaves evolve via a complex interplay of regulatory factors that ultimately influence cell proliferation and subsequent post-mitotic cell enlargement. During their development, a sequence of key events that shape leaves is both robustly executed spatiotemporally following a genomic molecular network and flexibly tuned by a variety of environmental stimuli. Decades of work on Arabidopsis thaliana have revisited the compensatory phenomena that might reflect a general and primary size-regulatory mechanism in leaves. This review focuses on key molecular and cellular events behind the organ-wide scale regulation of compensatory mechanisms. Lastly, emerging novel mechanisms of metabolic and hormonal regulation are discussed, based on recent advances in the field that have provided insights into, among other phenomena, leaf-size regulation.

Comprehensive Profiling of Phosphomonoester Metabolites in Saccharomyces cerevisiae by the Chemical Isotope Labeling-LC-MS Method

Phosphomonoesters are important biosynthetic and energy metabolism intermediates in microorganisms. A comprehensive analysis of phosphomonoester metabolites is of great significance for the understanding of their metabolic phosphorylation process and inner mechanism. In this study, we established a pair of isotope reagent d₀/d₅-2-diazomethyl-N-methyl-phenyl benzamide-labeling-based LC-MS method for the comprehensive analysis of phosphomonoester metabolites. By this method, the labeled phosphomonoester metabolites specifically produced characteristic isotope paired peaks with an m/z difference of 5.0314 in the MS¹ spectra and a pair of diagnostic ions (m/z 320.0693/325.1077) in the MS² spectra. Based on this, a diagnostic ion-based strategy was established for the rapid screening, identification, and relative quantification of phosphomonoester metabolites. Using this strategy, 42 phosphomonoester metabolites were highly accurately identified fromSaccharomyces cerevisiae (S. cerevisiae). Notably, two phosphomonoesters were first detected fromS. cerevisiae. The relative quantification results indicated that the contents of nine phosphomonoester metabolites including two intermediates (Ru5P and S7P) in the pentose phosphate pathway (PPP) were significantly different between lycopene-producible and wild-type S. cerevisiae. A further enzyme assay indicated that the activity of the PPP was closely related to the production of lycopene. Our findings provide new perspectives for the related mechanism study and valuable references for making informed microbial engineering decisions.

Skotomorphogenesis exploits threonine to promote hypocotyl elongation

Mobilisation of seed storage reserves is important for seedling establishment in Arabidopsis. In this process, sucrose is synthesised from triacylglycerol via core metabolic processes. Mutants with defects in triacylglycerol-to-sucrose conversion display short etiolated seedlings. We found that whereas sucrose content in the indole-3-butyric acid response 10 (ibr10) mutant was significantly reduced, hypocotyl elongation in the dark was unaffected, questioning the role of IBR10 in this process. To dissect the metabolic complexity behind cell elongation, a quantitative-based phenotypic analysis combined with a multi-platform metabolomics approach was applied. We revealed that triacylglycerol and diacylglycerol breakdown were disrupted in ibr10, resulting in low sugar content and poor photosynthetic ability. Importantly, batch-learning self-organised map clustering revealed that threonine level was correlated with hypocotyl length. Consistently, exogenous threonine supply stimulated hypocotyl elongation, indicating that sucrose levels are not always correlated with etiolated seedling length, suggesting the contribution of amino acids in this process.

The Mechanisms Underlying Salt Resistance Mediated by Exogenous Application of 24-Epibrassinolide in Peanut

Peanut is one of the most important oil crops in the world, the growth and productivity of which are severely affected by salt stress. 24-epibrassinolide (EBL) plays an important role in stress resistances. However, the roles of exogenous EBL on the salt tolerance of peanut remain unclear. In this study, peanut seedlings treated with 150 mM NaCl and with or without EBL spray were performed to investigate the roles of EBL on salt resistance. Under 150 mM NaCl conditions, foliar application of 0.1 µM EBL increased the activity of catalase and thereby could eliminate reactive oxygen species (ROS). Similarly, EBL application promoted the accumulation of proline and soluble sugar, thus maintaining osmotic balance. Furthermore, foliar EBL spray enhanced the total chlorophyll content and high photosynthesis capacity. Transcriptome analysis showed that under NaCl stress, EBL treatment up-regulated expression levels of genes encoding peroxisomal nicotinamide adenine dinucleotide carrier (PMP34), probable sucrose-phosphate synthase 2 (SPS2) beta-fructofuranosidase (BFRUCT1) and Na⁺/H⁺ antiporters (NHX7 and NHX8), while down-regulated proline dehydrogenase 2 (PRODH). These findings provide valuable resources for salt resistance study in peanut and lay the foundation for using BR to enhance salt tolerance during peanut production.

An auxin signaling network translates low-sugar-state input into compensated cell enlargement in the fugu5 cotyledon

In plants, the effective mobilization of seed nutrient reserves is crucial during germination and for seedling establishment. The Arabidopsis H+-PPase-loss-of-function fugu5 mutants exhibit a reduced number of cells in the cotyledons. This leads to enhanced post-mitotic cell expansion, also known as compensated cell enlargement (CCE). While decreased cell numbers have been ascribed to reduced gluconeogenesis from triacylglycerol, the molecular mechanisms underlying CCE remain ill-known. Given the role of indole 3-butyric acid (IBA) in cotyledon development, and because CCE in fugu5 is specifically and completely cancelled by ech2, which shows defective IBA-to-indoleacetic acid (IAA) conversion, IBA has emerged as a potential regulator of CCE. Here, to further illuminate the regulatory role of IBA in CCE, we used a series of high-order mutants that harbored a specific defect in IBA-to-IAA conversion, IBA efflux, IAA signaling, or vacuolar type H+-ATPase (V-ATPase) activity and analyzed the genetic interaction with fugu5-1. We found that while CCE in fugu5 was promoted by IBA, defects in IBA-to-IAA conversion, IAA response, or the V-ATPase activity alone cancelled CCE. Consistently, endogenous IAA in fugu5 reached a level 2.2-fold higher than the WT in 1-week-old seedlings. Finally, the above findings were validated in icl-2, mls-2, pck1-2 and ibr10 mutants, in which CCE was triggered by low sugar contents. This provides a scenario in which following seed germination, the low-sugar-state triggers IAA synthesis, leading to CCE through the activation of the V-ATPase. These findings illustrate how fine-tuning cell and organ size regulation depend on interplays between metabolism and IAA levels in plants.

Long chain acyl CoA synthetase 4 catalyzes the first step in peroxisomal indole-3-butyric acid to IAA conversion

Indole-3-butyric acid (IBA) is an endogenous storage auxin important for maintaining appropriate indole-3-acetic acid (IAA) levels, thereby influencingprimary root elongation and lateral root development. IBA is metabolized into free IAA in peroxisomes in a multistep process similar to fatty acid β-oxidation. We identified LONG CHAIN ACYL-COA SYNTHETASE 4 (LACS4) in a screen for enhanced IBA resistance in primary root elongation in Arabidopsis thaliana. LACSs activate substrates by catalyzing the addition of CoA, the necessary first step for fatty acids to participate in β-oxidation or other metabolic pathways. Here, we describe the novel role of LACS4 in hormone metabolism and postulate that LACS4 catalyzes the addition of CoA onto IBA, the first step in its β-oxidation. lacs4 is resistant to the effects of IBA in primary root elongation and dark-grown hypocotyl elongation, and has reduced lateral root density. lacs6 also is resistant to IBA, although both lacs4 and lacs6 remain sensitive to IAA in primary root elongation, demonstrating that auxin responses are intact. LACS4 has in vitro enzymatic activity on IBA, but not IAA or IAA conjugates, and disruption of LACS4 activity reduces the amount of IBA-derived IAA in planta. We conclude that, in addition to activity on fatty acids, LACS4 and LACS6 also catalyze the addition of CoA onto IBA, the first step in IBA metabolism and a necessary step in generating IBA-derived IAA.

Glycerolipid profile differences between perennial and annual stem zones in the perennial model plant Arabis alpina

The perennial life style is a successful ecological strategy, and Arabis alpina is a recently developed model Brassicaceae species for studying it. One aspect, poorly investigated until today, concerns the differing patterns of allocation, storage, and metabolism of nutrients between perennials and annuals and the yet unknown signals that regulate this process. A. alpina has a complex lateral stem architecture with a proximal vegetative perennial (PZ) and a distal annual flowering zone (AZ) inside the same stems. Lipid bodies (LBs) with triacylglycerols (TAGs) accumulate in the PZ. To identify potential processes of lipid metabolism linked with the perennial lifestyle, we analyzed lipid species in the PZ versus AZ. Glycerolipid fractions, including neutral lipids with mainly TAGs, phospholipids, and glycolipids, were present at higher levels in the PZ as compared to AZ or roots. Concomitantly, contents of specific long-chain and very long-chain fatty acids increased during formation of the PZ. Corresponding gene expression data, gene ontology term enrichment, and correlation analysis with lipid species pinpoint glycerolipid-related genes to be active during the development of the PZ. Possibilities that lipid metabolism genes may be targets of regulatory mechanisms specifying PZ differentiation in A. alpina are discussed.

Chemical Genetics Approach Identifies Abnormal Inflorescence Meristem 1 as a Putative Target of a Novel Sulfonamide That Protects Catalase2-Deficient Arabidopsis against Photorespiratory Stress

Alterations of hydrogen peroxide (H₂O₂) levels have a profound impact on numerous signaling cascades orchestrating plant growth, development, and stress signaling, including programmed cell death. To expand the repertoire of known molecular mechanisms implicated in H₂O₂ signaling, we performed a forward chemical screen to identify small molecules that could alleviate the photorespiratory-induced cell death phenotype of Arabidopsisthaliana mutants lacking H₂O₂-scavenging capacity by peroxisomal catalase2. Here, we report the characterization of pakerine, an m-sulfamoyl benzamide from the sulfonamide family. Pakerine alleviates the cell death phenotype of cat2 mutants exposed to photorespiration-promoting conditions and delays dark-induced senescence in wild-type Arabidopsis leaves. By using a combination of transcriptomics, metabolomics, and affinity purification, we identified abnormal inflorescence meristem 1 (AIM1) as a putative protein target of pakerine. AIM1 is a 3-hydroxyacyl-CoA dehydrogenase involved in fatty acid β-oxidation that contributes to jasmonic acid (JA) and salicylic acid (SA) biosynthesis. Whereas intact JA biosynthesis was not required for pakerine bioactivity, our results point toward a role for β-oxidation-dependent SA production in the execution of H₂O₂-mediated cell death.

Peroxisomes: versatile organelles with diverse roles in plants

Peroxisomes are small, ubiquitous organelles that are delimited by a single membrane and lack genetic material. However, these simple-structured organelles are highly versatile in morphology, abundance and protein content in response to various developmental and environmental cues. In plants, peroxisomes are essential for growth and development and perform diverse metabolic functions, many of which are carried out coordinately by peroxisomes and other organelles physically interacting with peroxisomes. Recent studies have added greatly to our knowledge of peroxisomes, addressing areas such as the diverse proteome, regulation of division and protein import, pexophagy, matrix protein degradation, solute transport, signaling, redox homeostasis and various metabolic and physiological functions. This review summarizes our current understanding of plant peroxisomes, focusing on recent discoveries. Current problems and future efforts required to better understand these organelles are also discussed. An improved understanding of peroxisomes will be important not only to the understanding of eukaryotic cell biology and metabolism, but also to agricultural efforts aimed at improving crop performance and defense.