Biochemical diversity among the 1-amino-cyclopropane-1-carboxylate synthase isozymes encoded by the Arabidopsis gene family

Genome-wide identification of polyamine metabolism and ethylene synthesis genes in Chenopodium quinoa Willd. and their responses to low-temperature stress

BACKGROUND

Quinoa (Chenopodium quinoa Willd.) is valued for its nutritional richness. However, pre-harvest sprouting poses a significant threat to yield and grain quality. This study aims to enhance our understanding of pre-harvest sprouting mitigation strategies, specifically through delayed sowing and avoiding rainy seasons during quinoa maturation. The overarching goal is to identify cold-resistant varieties and unravel the molecular mechanisms behind the low-temperature response of quinoa. We employed bioinformatics and genomics tools for a comprehensive genome-wide analysis of polyamines (PAs) and ethylene synthesis gene families in quinoa under low-temperature stress.

RESULTS

This involved the identification of 37 PA biosynthesis and 30 PA catabolism genes, alongside 227 ethylene synthesis. Structural and phylogenetic analyses showcased conserved patterns, and subcellular localization predictions indicated diverse cellular distributions. The results indicate that the PA metabolism of quinoa is closely linked to ethylene synthesis, with multiple genes showing an upregulation in response to cold stress. However, differential expression within gene families suggests a nuanced regulatory network.

CONCLUSIONS

Overall, this study contributes valuable insights for the functional characterization of the PA metabolism and ethylene synthesis of quinoa, which emphasize their roles in plant low-temperature tolerance and providing a foundation for future research in this domain.

Recent advances in understanding the regulation of plant secondary metabolite biosynthesis by ethylene-mediated pathways

Plants produce a large repertoire of secondary metabolites. The pathways that lead to the biosynthesis of these metabolites are majorly conserved in the plant kingdom. However, a significant portion of these metabolites are specific to certain groups or species due to variations in the downstream pathways and evolution of the enzymes. These metabolites show spatiotemporal variation in their accumulation and are of great importance to plants due to their role in development, stress response and survival. A large number of these metabolites are in huge industrial demand due to their potential use as therapeutics, aromatics and more. Ethylene, as a plant hormone is long known, and its biosynthetic process, signaling mechanism and effects on development and response pathways have been characterized in many plants. Through exogenous treatments, ethylene and its inhibitors have been used to manipulate the production of various secondary metabolites. However, the research done on a limited number of plants in the last few years has only started to uncover the mechanisms through which ethylene regulates the accumulation of these metabolites. Often in association with other hormones, ethylene participates in fine-tuning the biosynthesis of the secondary metabolites, and brings specificity in the regulation depending on the plant, organ, tissue type and the prevailing conditions. This review summarizes the related studies, interprets the outcomes, and identifies the gaps that will help to breed better varieties of the related crops and produce high-value secondary metabolites for human benefits.

Identification of Key Ubiquitination Sites Involved in the Proteasomal Degradation of AtACS7 in Arabidopsis

The gaseous hormone ethylene plays pivotal roles in plant growth and development. The rate-limiting enzyme of ethylene biosynthesis in seed plants is 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS). ACS proteins are encoded by a multigene family and the expression of ACS genes is highly regulated, especially at a post-translational level. AtACS7, the only type III ACS in Arabidopsis, is degraded in a 26S proteasome-dependent pathway. Here, by using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) analysis, two lysine residues of AtACS7, lys285 (K285) and lys366 (K366), were revealed to be ubiquitin-modified in young, light-grown Arabidopsis seedlings but not in etiolated seedlings. Deubiquitylation-mimicking mutations of these residues significantly increased the stability of the AtACS7K285RK366R mutant protein in cell-free degradation assays. All results suggest that K285 and K366 are the major ubiquitination sites on AtACS7, providing deeper insights into the post-translational regulation of AtACS7 in Arabidopsis.

Overexpression of cat2 restores antioxidant properties and production traits in degenerated strains of Volvariella volvacea

Strain degeneration is an important factor hindering the development of the edible fungus industry. Strain degeneration is associated with the excessive accumulation of reactive oxygen species (ROS) in vivo. Catalase (CAT), an important antioxidant enzyme, can promote the clearance of ROS. In this study, the cat2 gene of Volvariella volvacea was first cloned into an overexpression plasmid via homologous recombination. Finally, through Agrobacterium-mediated transformation, this plasmid was inserted into degenerated strains of V. volvacea T19. The physiological properties, antioxidant properties, ROS content, matrix degradation activity, and cultivation properties of the transformants were tested. The results showed that the cloned cat2 gene was 99.94% similar to the reference sequence. Screening revealed that six positive transformants were successfully obtained. After the overexpression of cat2, the growth rate and biomass of the mycelium increased significantly in the transformant strains (versus the V. volvacea T19 degenerated strains). Moreover, the accumulation of superoxide radical (O2•-) and hydrogen peroxide (H2O2) was significantly reduced, and the activity of the enzymes CAT, superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPX) was significantly increased. Meanwhile, the expression of cat2, Mnsod1, Mnsod2, gpx, and gr was significantly upregulated, and the activity of eight matrix degradation-related enzymes was increased to varying degrees. More importantly, the overexpression of the cat2 gene promoted the regrowth of fruiting bodies in degenerated strains of V. volvacea T19. This study provides a new biotechnological strategy to control the degeneration of V. volvacea and other edible fungi.

Exploring ethylene-related genes in Cannabis sativa: implications for sexual plasticity

KEY MESSAGE

Presented here are model Yang cycle, ethylene biosynthesis and signaling pathways in Cannabis sativa. C. sativa floral transcriptomes were used to predict putative ethylene-related genes involved in sexual plasticity in the species. Sexual plasticity is a phenomenon, wherein organisms possess the ability to alter their phenotypic sex in response to environmental and physiological stimuli, without modifying their sex chromosomes. Cannabis sativa L., a medically valuable plant species, exhibits sexual plasticity when subjected to specific chemicals that influence ethylene biosynthesis and signaling. Nevertheless, the precise contribution of ethylene-related genes (ERGs) to sexual plasticity in cannabis remains unexplored. The current study employed Arabidopsis thaliana L. as a model organism to conduct gene orthology analysis and reconstruct the Yang Cycle, ethylene biosynthesis, and ethylene signaling pathways in C. sativa. Additionally, two transcriptomic datasets comprising male, female, and chemically induced male flowers were examined to identify expression patterns in ERGs associated with sexual determination and sexual plasticity. These ERGs involved in sexual plasticity were categorized into two distinct expression patterns: floral organ concordant (FOC) and unique (uERG). Furthermore, a third expression pattern, termed karyotype concordant (KC) expression, was proposed, which plays a role in sex determination. The study revealed that CsERGs associated with sexual plasticity are dispersed throughout the genome and are not limited to the sex chromosomes, indicating a widespread regulation of sexual plasticity in C. sativa.

The Ethylene Biosynthetic Enzymes, 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase (ACS) and ACC Oxidase (ACO): The Less Explored Players in Abiotic Stress Tolerance

Ethylene is an essential plant hormone, critical in various physiological processes. These processes include seed germination, leaf senescence, fruit ripening, and the plant's response to environmental stressors. Ethylene biosynthesis is tightly regulated by two key enzymes, namely 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxidase (ACO). Initially, the prevailing hypothesis suggested that ACS is the limiting factor in the ethylene biosynthesis pathway. Nevertheless, accumulating evidence from various studies has demonstrated that ACO, under specific circumstances, acts as the rate-limiting enzyme in ethylene production. Under normal developmental processes, ACS and ACO collaborate to maintain balanced ethylene production, ensuring proper plant growth and physiology. However, under abiotic stress conditions, such as drought, salinity, extreme temperatures, or pathogen attack, the regulation of ethylene biosynthesis becomes critical for plants' survival. This review highlights the structural characteristics and examines the transcriptional, post-transcriptional, and post-translational regulation of ACS and ACO and their role under abiotic stress conditions. Reviews on the role of ethylene signaling in abiotic stress adaptation are available. However, a review delineating the role of ACS and ACO in abiotic stress acclimation is unavailable. Exploring how particular ACS and ACO isoforms contribute to a specific plant's response to various abiotic stresses and understanding how they are regulated can guide the development of focused strategies. These strategies aim to enhance a plant's ability to cope with environmental challenges more effectively.

Genome-wide in-silico analysis of ethylene biosynthesis gene family in Musa acuminata L. and their response under nutrient stress

Ethylene is a gaseous phytohormone involved in plants' growth and developmental processes, including seed germination, root initiation, fruit ripening, flower and leaf senescence, abscission, and stress responses. Ethylene biosynthesis (EB) gene analysis in response to nitrogen (N) and potassium (K) stress has not yet been conducted in Musa acuminata (banana) roots. The genome mining of banana (Musa acuminata L.) revealed 14 putative 1-aminocyclopropane-1-carboxylate synthase (ACS), 10 1-aminocyclopropane-1-carboxylate oxidase (ACO), and 3 Ethylene overproducer 1 (ETO1) genes. ACS, ACO, and ETO1 proteins possessed amino acid residues ranging from 422-684, 636-2670, and 893-969, respectively, with molecular weight (Mw) ranging from 4.93-7.55 kD, 10.1-8.3 kD and 10.1-10.78 kD. The number of introns present in ACS, ACO, and ETO1 gene sequences ranges from 0-14, 1-6, and 0-6, respectively. The cis-regulatory element analysis revealed the presence of light-responsive, abscisic acid, seed regulation, auxin-responsive, gibberellin element, endosperm-specific, anoxic inducibility, low-temperature responsiveness, salicylic acid responsiveness, meristem-specific and stress-responsive elements. Comprehensive phylogenetic analyses ACS, ACO, and ETO1 genes of Banana with Arabidopsis thaliana revealed several orthologs and paralogs assisting in understanding the putative functions of these genes. The expression profile of Musa acuminata genes in root under normal and low levels of nitrogen and potassium shows that MaACS14 and MaACO6 expressed highly at normal nitrogen supply. MaACS1 expression was significantly upregulated at low potassium levels, whereas, MaACO6 gene expression was significantly downregulated. The functional divergence and site-specific selective pressures on specific gene sequences of banana have been investigated. The bioinformatics-based genome-wide assessment of the family of banana attempted in the present study could be a significant step for deciphering novel ACS, ACO, and ETO1 genes based on genome-wide expression profiling.

Genome-Wide Identification and Expression Analysis of 1-Aminocyclopropane-1-Carboxylate Synthase (ACS) Gene Family in Chenopodium quinoa

Ethylene plays an important role in plant development and stress resistance. The rate-limiting enzyme in ethylene biosynthesis is 1-aminocyclopropane-1-carboxylic acid synthase (ACS). C. quinoa (Chenopodium quinoa) is an important food crop known for its strong tolerance to abiotic stresses. However, knowledge regarding the ACS gene family in C. quinoa remains restricted. In this study, we successfully identified 12 ACS genes (CqACSs) from the C. quinoa genome. Through thorough analysis of their sequences and phylogenetic relationships, it was verified that 8 out of these 12 CqACS isozymes exhibited substantial resemblance to ACS isozymes possessing ACS activity. Furthermore, these eight isozymes could be categorized into three distinct groups. The four remaining CqACS genes grouped under category IV displayed notable similarities with AtACS10 and AtACS12, known as amido transferases lacking ACS activity. The CqACS proteins bore resemblance to the AtACS proteins and had the characteristic structural features typically observed in plant ACS enzymes. Twelve CqACS genes were distributed across 8 out of the 18 chromosomes of C. quinoa. The CqACS genes were expanded from segment duplication. Many cis-regulatory elements related with various abiotic stresses, phytohormones, and light were found. The expression patterns of ACS genes varied across different tissues of C. quinoa. Furthermore, the analysis of gene expression patterns under abiotic stress showed that CqACS genes can be responsive to various stresses, implying their potential functions in adapting to various abiotic stresses. The findings from this research serve as a foundation for delving deeper into the functional roles of CqACS genes.

Biosynthetic Pathways of Hormones in Plants

Phytohormones exhibit a wide range of chemical structures, though they primarily originate from three key metabolic precursors: amino acids, isoprenoids, and lipids. Specific amino acids, such as tryptophan, methionine, phenylalanine, and arginine, contribute to the production of various phytohormones, including auxins, melatonin, ethylene, salicylic acid, and polyamines. Isoprenoids are the foundation of five phytohormone categories: cytokinins, brassinosteroids, gibberellins, abscisic acid, and strigolactones. Furthermore, lipids, i.e., α-linolenic acid, function as a precursor for jasmonic acid. The biosynthesis routes of these different plant hormones are intricately complex. Understanding of these processes can greatly enhance our knowledge of how these hormones regulate plant growth, development, and physiology. This review focuses on detailing the biosynthetic pathways of phytohormones.

Genome-Wide Analysis and Identification of 1-Aminocyclopropane-1-Carboxylate Synthase (ACS) Gene Family in Wheat (Triticum aestivum L.)

Ethylene has an important role in regulating plant growth and development as well as responding to adversity stresses. The 1-aminocyclopropane-1-carboxylate synthase (ACS) is the rate-limiting enzyme for ethylene biosynthesis. However, the role of the ACS gene family in wheat has not been examined. In this study, we identified 12 ACS members in wheat. According to their position on the chromosome, we named them TaACS1-TaACS12, which were divided into four subfamilies, and members of the same subfamilies had similar gene structures and protein-conserved motifs. Evolutionary analysis showed that fragment replication was the main reason for the expansion of the TaACS gene family. The spatiotemporal expression specificity showed that most of the members had the highest expression in roots, and all ACS genes contained W box elements that were related to root development, which suggested that the ACS gene family might play an important role in root development. The results of the gene expression profile analysis under stress showed that ACS members could respond to a variety of stresses. Protein interaction prediction showed that there were four types of proteins that could interact with TaACS. We also obtained the targeting relationship between TaACS family members and miRNA. These results provided valuable information for determining the function of the wheat ACS gene, especially under stress.

A role for ethylene signaling and biosynthesis in regulating and accelerating CO2 - and abscisic acid-mediated stomatal movements in Arabidopsis

Little is known about long-distance mesophyll-driven signals that regulate stomatal conductance. Soluble and/or vapor-phase molecules have been proposed. In this study, the involvement of the gaseous signal ethylene in the modulation of stomatal conductance in Arabidopsis thaliana by CO2 /abscisic acid (ABA) was examined. We present a diffusion model which indicates that gaseous signaling molecule/s with a shorter/direct diffusion pathway to guard cells are more probable for rapid mesophyll-dependent stomatal conductance changes. We, therefore, analyzed different Arabidopsis ethylene-signaling and biosynthesis mutants for their ethylene production and kinetics of stomatal responses to ABA/[CO2 ]-shifts. According to our research, higher [CO2 ] causes Arabidopsis rosettes to produce more ethylene. An ACC-synthase octuple mutant with reduced ethylene biosynthesis exhibits dysfunctional CO2 -induced stomatal movements. Ethylene-insensitive receptor (gain-of-function), etr1-1 and etr2-1, and signaling, ein2-5 and ein2-1, mutants showed intact stomatal responses to [CO2 ]-shifts, whereas loss-of-function ethylene receptor mutants, including etr2-3;ein4-4;ers2-3, etr1-6;etr2-3 and etr1-6, showed markedly accelerated stomatal responses to [CO2 ]-shifts. Further investigation revealed a significantly impaired stomatal closure to ABA in the ACC-synthase octuple mutant and accelerated stomatal responses in the etr1-6;etr2-3, and etr1-6, but not in the etr2-3;ein4-4;ers2-3 mutants. These findings suggest essential functions of ethylene biosynthesis and signaling components in tuning/accelerating stomatal conductance responses to CO2 and ABA.

Roles of S-Adenosylmethionine and Its Derivatives in Salt Tolerance of Cotton

Salinity is a major abiotic stress that restricts cotton growth and affects fiber yield and quality. Although studies on salt tolerance have achieved great progress in cotton since the completion of cotton genome sequencing, knowledge about how cotton copes with salt stress is still scant. S-adenosylmethionine (SAM) plays important roles in many organelles with the help of the SAM transporter, and it is also a synthetic precursor for substances such as ethylene (ET), polyamines (PAs), betaine, and lignin, which often accumulate in plants in response to stresses. This review focused on the biosynthesis and signal transduction pathways of ET and PAs. The current progress of ET and PAs in regulating plant growth and development under salt stress has been summarized. Moreover, we verified the function of a cotton SAM transporter and suggested that it can regulate salt stress response in cotton. At last, an improved regulatory pathway of ET and PAs under salt stress in cotton is proposed for the breeding of salt-tolerant varieties.

Impacts of DNA methylases and demethylases on the methylation and expression of Arabidopsis ethylene signal pathway genes

Arabidopsis ethylene (ET) signal pathway plays important roles in various aspects. Cytosine DNA methylation is significant in controlling gene expression in plants. Here, we analyzed the bisulfite sequencing and mRNA sequencing data from Arabidopsis (de)methylase mutants met1, cmt3, drm1/2, ddm1, ros1-4, and rdd to investigate how DNA (de)methylases influence the DNA methylation and expression of Arabidopsis ET pathway genes. At least 32 genes are found to involved in Arabidopsis ET pathway by text mining. Among them, 14 genes are unmethylated or methylated with very low levels. ACS6 and ACS9 are conspicuously methylated within their upstream regions. The other 16 genes are predominantly methylated at the CG sites within gene body regions in wild-type plants, and mutation of MET1 resulted in almost entire elimination of the CG methylations. In addition, CG methylations within some genes are jointly maintained by MET1 and other (de)methylases. Analyses of mRNA-seq data indicated that some ET pathway genes were differentially expressed between wild-type and diverse mutants. PDF1.2, the marker gene of ET signal pathway, was found being regulated indirectly by the methylases. Eighty-two transposable elements (TEs) were identified to be associated to 15 ET pathway genes. ACS11 is found located in a heterochromatin region that contains 57 TEs, indicating its specific expression and regulation. Together, our results suggest that DNA (de)methylases are implicated in the regulation of CG methylation within gene body regions and transcriptional activity of some ET pathway genes and that maintenance of normal CG methylation is essential for ET pathway in Arabidopsis.

Domain Swapping between AtACS7 and PpACL1 Results in Chimeric ACS-like Proteins with ACS or Cβ-S Lyase Single Enzymatic Activity

The gaseous hormone ethylene plays a pivotal role in plant growth and development. In seed plants, the key rate-limiting enzyme that controls ethylene biosynthesis is ACC synthase (ACS). ACS has, for a long time, been believed to be a single-activity enzyme until we recently discovered that it also possesses C_β-S lyase (CSL) activity. This discovery raises fundamental questions regarding the biological significance of the dual enzymatic activities of ACS. To address these issues, it is highly necessary to obtain ACS mutants with either ACS or CSL single activity. Here, domain swapping between Arabidopsis AtACS7 and moss CSL PpACL1 were performed. Enzymatic activity assays of the constructed chimeras revealed that, R10, which was produced by replacing AtACS7 box 6 with that of PpACL1, lost ACS but retained CSL activity, whereas R12 generated by box 4 substitution lost CSL and only had ACS activity. The activities of both chimeric proteins were compared with previously obtained single-activity mutants including R6, AtACS7^Q98A, and AtACS7^D245N. All the results provided new insights into the key residues required for ACS and CSL activities of AtACS7 and laid an important foundation for further in-depth study of the biological functions of its dual enzymatic activities.

WRKY29 transcription factor regulates ethylene biosynthesis and response in arabidopsis

The gaseous phytohormone ethylene participates in a lot of physiological processes in plants. 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS, EC 4.4.1.14) and the ACC oxidase (ACO, EC 1.14.17.4) are key enzymes in ethylene biosynthesis. However, how ACSs and ACOs are regulated at the transcriptional level is largely unknown. In the present study, we showed that an Arabidopsis (Arabidopsis thaliana) WRKY-type transcription factor (TF), WRKY29 positively regulated the expression of ACS5, ACS6, ACS8, ACS11 and ACO5 genes and thus promoted basal ethylene production. WRKY29 protein was localized in nuclei and was a transcriptional activator. Overexpression of WRKY29 caused pleiotropic effect on plant growth, development and showed obvious response even without ACC treatment. Inducible overexpression of WRKY29 also reduced primary root elongation and lateral root growth. A triple response assay of overexpression and mutant seedlings of WRKY29 showed that overexpression seedlings had shorter hypocotyls than the transgenic GFP (Green Fluorescence Protein) control, while mutants had no difference from wild-type. A qRT-PCR assay demonstrated that expression of multiple ACSs and ACO5 was up-regulated in WRKY29 overexpression plants. A transactivation assay through dual luciferase reporter system confirmed the regulation of promoters of ACS5, ACS6, ACS8, ACS11 and ACO5 by WRKY29. Both in vivo chromatin immunoprecipitation (ChIP)- quantitative PCR and in vitro electrophoretic mobility shift assay (EMSA) revealed that WRKY29 directly bound to the promoter regions of its target genes. Taken together, these results suggest that WRKY29 is a novel TF positively regulating ethylene production by modulating the expression of ACS and ACO genes.

Transcriptome Dynamics of Rooting Zone and Leaves during In Vitro Adventitious Root Formation in Eucalyptus nitens

Wood properties and agronomic traits associated with fast growth and frost tolerance make Eucalyptus nitens a valuable forest alternative. However, the rapid age-related decline in the adventitious root (AR) formation (herein, meaning induction, initiation, and expression stages) limits its propagation. We analyzed transcriptomic profile variation in leaves and stem bases during AR induction of microcuttings to elucidate the molecular mechanisms involved in AR formation. In addition, we quantified expressions of candidate genes associated with recalcitrance. We delimited the ontogenic phases of root formation using histological techniques and Scarecrow and Short-Root expression quantification for RNA sequencing sample collection. We quantified the gene expressions associated with root meristem formation, auxin biosynthesis, perception, signaling, conjugation, and cytokinin signaling in shoots harvested from 2- to 36-month-old plants. After IBA treatment, 702 transcripts changed their expressions. Several were involved in hormone homeostasis and the signaling pathways that determine cell dedifferentiation, leading to root meristem formation. In part, the age-related decline in the rooting capacity is attributable to the increase in the ARR1 gene expression, which negatively affects auxin homeostasis. The analysis of the transcriptomic variation in the leaves and rooting zones provided profuse information: (1) To elucidate the auxin metabolism; (2) to understand the hormonal and signaling processes involved; (3) to collect data associated with their recalcitrance.

Transcriptomic profiling analysis to identify genes associated with PA biosynthesis and insolubilization in the late stage of fruit development in C-PCNA persimmon

PA-enhanced content causes astringency in persimmon fruit. PCNA persimmons can lose their astringency naturally and they become edible when still on the tree, which allows for conserves of physical and financial resources. C-PCNA persimmon originates in China. Its deastringency trait primarily depends on decreased PA biosynthesis and PA insolubilization at the late stage of fruit development. Although some genes and transcription factors that may be involved in the deastringency of C-PCNA persimmon have been reported, the expression patterns of these genes during the key deastringency stage are reported less. To investigate the variation in PA contents and the expression patterns of deastringency-related genes during typical C-PCNA persimmon 'Xiaoguo-tianshi' fruit development and ripening, PA content and transcriptional profiling were carried out at five late stages from 70 to 160 DAF. The combinational analysis phenotype, PA content, and DEG enrichment revealed that 120-140 DAF and 140-160 DAF were the critical phases for PA biosynthesis reduction and PA insolubilization, respectively. The expression of PA biosynthesis-associated genes indicated that the downregulation of the ANR gene at 140-160 DAF may be associated with PA biosynthesis and is decreased by inhibiting its precursor cis-flavan-3-ols. We also found that a decrease in acetaldehyde metabolism-associated ALDH genes and an increase in ADH and PDC genes might result in C-PCNA persimmon PA insolubilization. In addition, a few MYB-bHLH-WD40 (MBW) homologous transcription factors in persimmon might play important roles in persimmon PA accumulation. Furthermore, combined coexpression network analysis and phylogenetic analysis of MBW suggested that three putative transcription factors WD40 (evm.TU.contig1.155), MYB (evm.TU.contig8910.486) and bHLH (evm.TU.contig1398.203), might connect and co-regulate both PA biosynthesis and its insolubilization in C-PCNA persimmon. The present study elucidated transcriptional insights into PA biosynthesis and insolubilization during the late development stages based on the C-PCNA D. kaki genome (unpublished). Thus, we focused on PA content variation and the expression patterns of genes involved in PA biosynthesis and insolubilization. Our work has provided additional evidence on previous knowledge and a basis for further exploration of the natural deastringency of C-PCNA persimmon.

Multigenic regulation in the ethylene biosynthesis pathway during coffee flowering

Ethylene regulates different aspects of the plant's life cycle, such as flowering, and acts as a defense signal in response to environmental stresses. Changes induced by water deficit (WD) in gene expression of the main enzymes involved in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and oxidase (ACO), are frequently reported in plants. In this study, coffee (Coffea arabica) ACS and ACO family genes were characterized and their expression profiles were analyzed in leaves, roots, flower buds, and open flowers from plants under well-watered (WW) and water deficit (WD) conditions. Three new ACS genes were identified. Water deficit did not affect ACS expression in roots, however soil drying strongly downregulated ACO expression, indicating a transcriptional constraint in the biosynthesis pathway during the drought that can suppress ethylene production in roots. In floral buds, ACO expression is water-independent, suggesting a higher mechanism of control in reproductive organs during the final flowering stages. Leaves may be the main sites for ethylene precursor (1-aminocyclopropane-1-carboxylic acid, ACC) production in the shoot under well-watered conditions, contributing to an increase in the ethylene levels required for anthesis. Given these results, we suggest a possible regulatory mechanism for the ethylene biosynthesis pathway associated with coffee flowering with gene regulation in leaves being a key point in ethylene production and ACO genes play a major regulatory role in roots and the shoots. This mechanism may constitute a regulatory model for flowering in other woody species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01235-y.

Genome-Wide Identification and Characterization of Members of the ACS Gene Family in Cucurbita maxima and Their Transcriptional Responses to the Specific Treatments

Ethylene biosynthesis and signal transduction play critical roles in plant sex differentiation. ACS (1-aminocyclopropane-1-carboxylic acid synthase) is a rate-limiting enzyme in ethylene biosynthesis. However, the understanding of the ACS gene family in Cucurbita maxima is limited. Here, we identified and characterized 13 ACS genes in the C. maxima genome. All ACS genes could be divided into three groups according to a conserved serine residue at the C-terminus. Thirteen CmaACS genes were found to be randomly distributed on 10 of the 20 chromosomes of C. maxima. The ACS gene exhibits different tissue-specific expression patterns in pumpkin, and four ACS genes (CmaACS1, CmaACS4, CmaACS7, and CmaACS9) were expressed specifically in both the female and male flowers of C. maxima. In addition, the expression levels of CmaACS4 and CmaACS7 were upregulated after ethephon and IAA treatments, which ultimately increased the number of female flowers, decreased the position of the first female flower and decreased the number of bisexual flowers per plant. These results provide relevant information for determining the function of the ACS genes in C. maxima, especially for regulating the function of ethylene in sex determination.

Discovery of a novel nucleoside immune signaling molecule 2'-deoxyguanosine in microbes and plants

INTRODUCTION

Beneficial microorganisms play essential roles in plant growth and induced systemic resistance (ISR) by releasing signaling molecules. Our previous study obtained the crude extract from beneficial endophyte Paecilomyces variotii, termed ZNC (ZhiNengCong), which significantly enhanced plant resistance to pathogen even at 100 ng/ml. However, the immunoreactive components of ZNC remain unclear. Here, we further identified one of the immunoreactive components of ZNC is a nucleoside 2'-deoxyguanosine (2-dG).

OBJECTIVES

This paper intends to reveal the molecular mechanism of microbial-derived 2'-deoxyguanosine (2-dG) in activating plant immunity, and the role of plant-derived 2-dG in plant immunity.

METHODS

The components of ZNC were separated using a high-performance liquid chromatography (HPLC), and 2-dG is identified using a HPLC-mass spectrometry system (LC-MS). Transcriptome analysis and genetic experiments were used to reveal the immune signaling pathway dependent on 2-dG activation of plant immunity.

RESULTS

This study identified 2'-deoxyguanosine (2-dG) as one of the immunoreactive components from ZNC. And 2-dG significantly enhanced plant pathogen resistance even at 10 ng/ml (37.42 nM). Furthermore, 2-dG-induced resistance depends on NPR1, pattern-recognition receptors/coreceptors, ATP receptor P2K1 (DORN1), ethylene signaling but not salicylic acid accumulation. In addition, we identified Arabidopsis VENOSA4 (VEN4) was involved in 2-dG biosynthesis and could convert dGTP to 2-dG, and vne4 mutant plants were more susceptible to pathogens.

CONCLUSION

In summary, microbial-derived 2-dG may act as a novel immune signaling molecule involved in plant-microorganism interactions, and VEN4 is 2-dG biosynthesis gene and plays a key role in plant immunity.

Glutathione contributes to plant defence against parasitic cyst nematodes

Cyst nematodes (CNs) are an important group of root-infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l-γ-glutamyl-l-cysteinyl-glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate-cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione-deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione-mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine-tuning the balance between the cellular redox environment and the production of compounds related to defence against infection.

Evolutionary Origin and Functional Diversification of Aminotransferases

Aminotransferases (ATs) are pyridoxal 5′-phosphate–dependent enzymes that catalyze the transamination reactions between amino acid donor and keto acid acceptor substrates. Modern AT enzymes constitute ∼2% of all classified enzymatic activities, play central roles in nitrogen metabolism, and generate multitude of primary and secondary metabolites. ATs likely diverged into four distinct AT classes before the appearance of the last universal common ancestor and further expanded to a large and diverse enzyme family. Although the AT family underwent an extensive functional specialization, many AT enzymes retained considerable substrate promiscuity and multifunctionality because of their inherent mechanistic, structural, and functional constraints. This review summarizes the evolutionary history, diverse metabolic roles, reaction mechanisms, and structure–function relationships of the AT family enzymes, with a special emphasis on their substrate promiscuity and multifunctionality. Comprehensive characterization of AT substrate specificity is still needed to reveal their true metabolic functions in interconnecting various branches of the nitrogen metabolic network in different organisms.

Potential Roles of 1-Aminocyclopropane-1-carboxylic Acid Synthase Genes in the Response of Gossypium Species to Abiotic Stress by Genome-Wide Identification and Expression Analysis

Ethylene plays a pivotal role in plant stress resistance and 1-aminocyclopropane-1-carboxylic acid synthase (ACS) is the rate-limiting enzyme in ethylene biosynthesis. Upland cotton (Gossypium hirsutum L.) is the most important natural fiber crop, but the function of ACS in response to abiotic stress has rarely been reported in this plant. We identified 18 GaACS, 18 GrACS, and 35 GhACS genes in Gossypiumarboreum, Gossypium raimondii and Gossypiumhirsutum, respectively, that were classified as types I, II, III, or IV. Collinearity analysis showed that the GhACS genes were expanded from diploid cotton by the whole-genome-duplication. Multiple alignments showed that the C-terminals of the GhACS proteins were conserved, whereas the N-terminals of GhACS10 and GhACS12 were different from the N-terminals of AtACS10 and AtACS12, probably diverging during evolution. Most type II ACS genes were hardly expressed, whereas GhACS10/GhACS12 were expressed in many tissues and in response to abiotic stress; for example, they were highly and hardly expressed at the early stages of cold and heat exposure, respectively. The GhACS genes showed different expression profiles in response to cold, heat, drought, and salt stress by quantitative PCR analysis, which indicate the potential roles of them when encountering the various adverse conditions, and provide insights into GhACS functions in cotton’s adaptation to abiotic stress.

The Oncidium Ethylene Synthesis Gene Oncidium 1-Aminocyclopropane-1 Carboxylic Acid Synthase 12 and Ethylene Receptor Gene Oncidium ETR1 Affect GA-DELLA and Jasmonic Acid Signaling in Regulating Flowering Time, Anther Dehiscence, and Flower Senescence in Arabidopsis

In plants, the key enzyme in ethylene biosynthesis is 1-aminocyclopropane-1 carboxylic acid (ACC) synthase (ACS), which catalyzes S-adenosyl-L-methionine (SAM) to ACC, the precursor of ethylene. Ethylene binds to its receptors, such as ethylene response 1 (ETR1), to switch on ethylene signal transduction. To understand the function of ACS and ETR1 in orchids, Oncidium ACC synthase 12 (OnACS12) and Oncidium ETR1 (OnETR1) from Oncidium Gower Ramsey were functionally analyzed in Arabidopsis. 35S::OnACS12 caused late flowering and anther indehiscence phenotypes due to its effect on GA-DELLA signaling pathways. 35S::OnACS12 repressed GA biosynthesis genes (CPS, KS, and GA3ox1), which caused the upregulation of DELLA [GA-INSENSITIVE (GAI), RGA-LIKE1 (RGL1), and RGL2] expression. The increase in DELLAs not only suppressed LEAFY (LFY) expression and caused late flowering but also repressed the jasmonic acid (JA) biosynthesis gene DAD1 and caused anther indehiscence by downregulating the endothecium-thickening-related genes MYB26, NST1, and NST2. The ectopic expression of an OnETR1 dominant-negative mutation (OnETR1-C65Y) caused both ethylene and JA insensitivity in Arabidopsis. 35S::OnETR1-C65Y delayed flower/leaf senescence by suppressing downstream genes in ethylene signaling, including EDF1-4 and ERF1, and in JA signaling, including MYC2 and WRKY33. JA signaling repression also resulted in indehiscent anthers via the downregulation of MYB26, NST1, NST2, and MYB85. These results not only provide new insight into the functions of ACS and ETR1 orthologs but also uncover their functional interactions with other hormone signaling pathways, such as GA-DELLA and JA, in plants.

Reduction of ethylene biosynthesis in sugarcane induces growth and investment in the non-enzymatic antioxidant apparatus

Lower ethylene production in sugarcane results in plants with higher stature, expression of growth-promoting genes, higher photosynthetic rate, and increased antioxidant compounds. The hormone ethylene is involved in critical processes in sugarcane, such as the growth and accumulation of sucrose. The lack of mutants for ethylene biosynthesis or signaling genes makes it difficult to understand the role of this phytohormone throughout sugarcane development. This study aimed to evaluate the physiology and development of sugarcane plants with low ethylene production. To achieve this goal, we used RNA interference to silence three genes, ScACS1, ScACS2, and ScACS3, encoding 1-aminocyclopropane-1-carboxylic acid synthases (ACS), responsible for a limiting step of the ethylene biosynthesis pathway. Sugarcane plants with reduced ethylene levels presented increased growth, faster germination of lateral gems, and activation of non-enzymatic antioxidant mechanisms. We observed an augmentation in the expression of ScACO5, which encodes the final enzyme regulating ethylene biosynthesis, and ScERF1, encoding a transcription factor, linked to the ethylene response. The increase in plant height was correlated with higher expression of ScPIF3, ScPIF4, and ScPIF5, which encode for transcription factors related to growth induction. Interestingly, there was also an increase in the expression of the ScGAI gene, which encodes a DELLA protein, a growth repressor. The final content of sucrose in the stems was not affected by the low levels of ethylene, although the rate of CO₂ assimilation was reduced. This study reports for the first time the impacts of low endogenous production of ethylene in sugarcane and provides helpful insights on the molecular mechanisms behind ethylene responses.

Dynamic roles and intricate mechanisms of ethylene in epidermal hair development in Arabidopsis and cotton

Ethylene affects many aspects of plant growth and development, including root hairs and trichomes growth in Arabidopsis, as well as fiber development in cotton, though the underlying mechanism is unclear. In this article, we update the research progress associated with the main genes in ethylene biosynthesis and signaling pathway, and we propose a clear ethylene pathway based on genome-wide identification of homologues in cotton. Expression pattern analysis using transcriptome data revealed that some candidate genes may contribute to cotton fiber development through the ethylene pathway. Moreover, we systematically summarized the effects of ethylene on the development of epidermal hair and the underlying regulatory mechanisms in Arabidopsis. Based on the knowledge of ethylene-promoted cell differentiation, elongation, and development in different tissues or plants, we advised a possible regulatory network for cotton fiber development with ethylene as the hub. Importantly, we emphasized the roles of ethylene as an important node in regulating cotton vegetative growth, and stress resistance, and suggested utilizing multiple methods to subtly modify ethylene synthesis or signaling in a tissue or spatiotemporal-specific manner to clarify its exact effect on architecture, adaptability of the plant, and fiber development, paving the way for basic research and genetic improvement of the cotton crop.

Regulation of Phytohormones on the Growth and Development of Plant Root Hair

The tubular-shaped unicellular extensions of plant epidermal cells known as root hairs are important components of plant roots and play crucial roles in absorbing nutrients and water and in responding to stress. The growth and development of root hair include, mainly, fate determination of root hair cells, root hair initiation, and root hair elongation. Phytohormones play important regulatory roles as signal molecules in the growth and development of root hair. In this review, we describe the regulatory roles of auxin, ethylene (ETH), jasmonate (JA), abscisic acid (ABA), gibberellin (GA), strigolactone (SL), cytokinin (CK), and brassinosteroid (BR) in the growth and development of plant root hairs. Auxin, ETH, and CK play positive regulation while BR plays negative regulation in the fate determination of root hair cells; Auxin, ETH, JA, CK, and ABA play positive regulation while BR plays negative regulation in the root hair initiation; Auxin, ETH, CK, and JA play positive regulation while BR, GA, and ABA play negative regulation in the root hair elongation. Phytohormones regulate root hair growth and development mainly by regulating transcription of root hair associated genes, including WEREWOLF (WER), GLABRA2 (GL2), CAPRICE (CPC), and HAIR DEFECTIVE 6 (RHD6). Auxin and ETH play vital roles in this regulation, with JA, ABA, SL, and BR interacting with auxin and ETH to regulate further the growth and development of root hairs.

Systematic genome-wide analysis of the ethylene-responsive ACS gene family: Contributions to sex form differentiation and development in melon and watermelon

Ethylene is an important regulatory phytohormone for sex differentiation and flower development. As the rate-limiting enzyme encoding genes in ethylene biosynthesis, ACS gene family has been well studied in cucumber; however, little is known in other cucurbit crops, such as melon and watermelon, which show diverse sex types in the field. Here, we identified and characterized eight ACS genes each in the genomes of melon and watermelon. According to the conserved serine residues at C-terminal, all the ACS genes could be characterized into three groups, which were supported by the exon-intron organizations and conserved motif distributions. ACS genes displayed diverse tissue-specific expression patterns among four melon and three watermelon sex types. Furthermore, a comparative expression analysis in the shoot apex identified orthologous pairs with potential functions in sex determination, e.g., ACS1s and ACS6s. All ACS orthologs in melon and watermelon exhibited similar expression patterns in monoecious and gynoecious genotypes, except for ACS11s and ACS12s. As expected, the majority of ACS genes were responsive to exogenous ethephon; however, some orthologs exhibited opposite expression patterns, such as ACS1s, ACS9s, and ACS10s. Collectively, our findings provide valuable ACS candidates related to flower development in various sex types of melon and watermelon.

Dual activities of ACC synthase: Novel clues regarding the molecular evolution of ACS genes

Ethylene plays profound roles in plant development. The rate-limiting enzyme of ethylene biosynthesis is 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS), which is generally believed to be a single-activity enzyme evolving from aspartate aminotransferases. Here, we demonstrate that, in addition to catalyzing the conversion of S-adenosyl-methionine to the ethylene precursor ACC, genuine ACSs widely have C_β-S lyase activity. Two N-terminal motifs, including a glutamine residue, are essential for conferring ACS activity to ACS-like proteins. Motif and activity analyses of ACS-like proteins from plants at different evolutionary stages suggest that the ACC-dependent pathway is uniquely developed in seed plants. A putative catalytic mechanism for the dual activities of ACSs is proposed on the basis of the crystal structure and biochemical data. These findings not only expand our current understanding of ACS functions but also provide novel insights into the evolutionary origin of ACS genes.

KAI2 promotes Arabidopsis root hair elongation at low external phosphate by controlling local accumulation of AUX1 and PIN2

Root hair (RH) growth to increase the absorptive root surface area is a key adaptation of plants to limiting phosphate availability in soils. Despite the importance of this trait, especially for seedling survival, little is known about the molecular events connecting phosphate starvation sensing and RH growth regulation. KARRIKIN INSENSITIVE2 (KAI2), an α/β-hydrolase receptor of a yet-unknown plant hormone ("KAI2-ligand" [KL]), is required for RH elongation.¹ KAI2 interacts with the F-box protein MORE AXILLIARY BRANCHING2 (MAX2) to target regulatory proteins of the SUPPRESSOR of MAX2 1 (SMAX1) family for degradation.² Here, we demonstrate that P_i starvation increases KL signaling in Arabidopsis roots through transcriptional activation of KAI2 and MAX2. Both genes are required for RH elongation under these conditions, while smax1 smxl2 mutants have constitutively long RHs, even at high P_i availability. Attenuated RH elongation in kai2 mutants is explained by reduced shootward auxin transport from the root tip resulting in reduced auxin signaling in the RH zone, caused by an inability to increase localized accumulation of the auxin importer AUXIN TRANSPORTER PROTEIN1 (AUX1) and the auxin exporter PIN-FORMED2 (PIN2) upon P_i starvation. Consistent with AUX1 and PIN2 accumulation being mediated via ethylene signaling,³ expression of 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE 7 (ACS7) is increased at low P_i in a KAI2-dependent manner, and treatment with an ethylene precursor restores RH elongation of acs7, but not of aux1 and pin2. Thus, KAI2 signaling is increased by phosphate starvation to trigger an ethylene- AUX1/PIN2-auxin cascade required for RH elongation.

Plants Saline Environment in Perception with Rhizosphere Bacteria Containing 1-Aminocyclopropane-1-Carboxylate Deaminase

Soil salinity stress has become a serious roadblock for food production worldwide since it is one of the key factors affecting agricultural productivity. Salinity and drought are predicted to cause considerable loss of crops. To deal with this difficult situation, a variety of strategies have been developed, including plant breeding, plant genetic engineering, and a wide range of agricultural practices, including the use of plant growth-promoting rhizobacteria (PGPR) and seed biopriming techniques, to improve the plants' defenses against salinity stress, resulting in higher crop yields to meet future human food demand. In the present review, we updated and discussed the negative effects of salinity stress on plant morphological parameters and physio-biochemical attributes via various mechanisms and the beneficial roles of PGPR with 1-Aminocyclopropane-1-Carboxylate(ACC) deaminase activity as green bio-inoculants in reducing the impact of saline conditions. Furthermore, the applications of ACC deaminase-producing PGPR as a beneficial tool in seed biopriming techniques are updated and explored. This strategy shows promise in boosting quick seed germination, seedling vigor and plant growth uniformity. In addition, the contentious findings of the variation of antioxidants and osmolytes in ACC deaminase-producing PGPR treated plants are examined.

Genome-Wide Identification of the 1-Aminocyclopropane-1-carboxylic Acid Synthase (ACS) Genes and Their Possible Role in Sand Pear (Pyrus pyrifolia) Fruit Ripening

Ethylene production is negatively associated with storage life in sand pear (Pyrus pyrifolia Nakai), particularly at the time of fruit harvest. 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) is the rate-limiting enzyme in ethylene biosynthesis and is considered to be important for fruit storage life. However, the candidate ACS genes and their roles in sand pear remain unclear. The present study identified 13 ACS genes from the sand pear genome. Phylogenetic analysis categorized these ACS genes into four subgroups (type I, type II, type III and putative AAT), and indicated a close relationship between sand pear and Chinese white pear (P. bretschneideri). According to the RNA-seq data and qRT-PCR analysis, PpyACS1, PpyACS2, PpyACS3, PpyACS8, PpyACS9, PpyACS12 and PpyACS13 were differently expressed in climacteric and non-climacteric-type pear fruits, ‘Ninomiyahakuri’ and ‘Eli No.2’, respectively, during fruit ripening. In addition, the expressions of PpyACS2, PpyACS8, PpyACS12 and PpyACS13 were found to be associated with system 1 of ethylene production, while PpyACS1, PpyACS3, and PpyACS9 were found to be associated with system 2, indicating that these ACS genes have different roles in ethylene biosynthesis during fruit development. Overall, our study provides fundamental knowledge on the characteristics of the ACS gene family in sand pear, in addition to their possible roles in fruit ripening.

Fusarium verticillioides Induces Maize-Derived Ethylene to Promote Virulence by Engaging Fungal G-Protein Signaling

Seed maceration and contamination with mycotoxin fumonisin inflicted by Fusarium verticillioides is a major disease concern for maize producers worldwide. Meta-analyses of quantitative trait loci for Fusarium ear rot resistance uncovered several ethylene (ET) biosynthesis and signaling genes within them, implicating ET in maize interactions with F. verticillioides. We tested this hypothesis using maize knockout mutants of the 1-aminocyclopropane-1-carboxylate (ACC) synthases ZmACS2 and ZmACS6. Infected wild-type seed emitted five-fold higher ET levels compared with controls, whereas ET was abolished in the acs2 and acs6 single and double mutants. The mutants supported reduced fungal biomass, conidia, and fumonisin content. Normal susceptibility was restored in the acs6 mutant with exogenous treatment of ET precursor ACC. Subsequently, we showed that fungal G-protein signaling is required for virulence via induction of maize-produced ET. F. verticillioides G_β subunit and two regulators of G-protein signaling mutants displayed reduced seed colonization and decreased ET levels. These defects were rescued by exogenous application of ACC. We concluded that pathogen-induced ET facilitates F. verticillioides colonization of seed, and, in turn, host ET production is manipulated via G-protein signaling of F. verticillioides to facilitate pathogenesis.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The regulation of ACC synthase protein turnover: a rapid route for modulating plant development and stress responses

The phytohormone ethylene regulates plant growth, development, and stress responses. The strict fine-tuning of the regulation of ethylene biosynthesis contributes to the diverse roles of ethylene in plants. Pyridoxal 5'-phosphate-dependent 1-aminocyclopropane-1-carboxylic acid synthase, a rate-limiting enzyme in ethylene biosynthesis, is central and often rate-limiting to regulate ethylene concentration in plants. The post-translational regulation of ACS is a major pathway controlling ethylene biosynthesis in response to various stimuli. We conclude that the regulation of ACS turnover may serve as a central hub for the rapid integration of developmental, environmental, and hormonal signals, all of which influence plant growth and stress responses.

Distinct Functions of Ethylene and ACC in the Basal Land Plant Marchantia polymorpha

Ethylene is a gaseous phytohormone involved in various physiological processes, including fruit ripening, senescence, root hair development and stress responses. Recent genomics studies have suggested that most homologous genes of ethylene biosynthesis and signaling are conserved from algae to angiosperms, whereas the function and biosynthesis of ethylene remain unknown in basal plants. Here, we examined the physiological effects of ethylene, an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) and an inhibitor of ethylene perception, silver thiosulfate (STS), in a basal land plant, Marchantia polymorpha. M. polymorpha plants biosynthesized ethylene, and treatment with high concentrations of ACC slightly promoted ethylene production. ACC remarkably suppressed the growth of thalli (vegetative organs) and rhizoids (root-hair-like cells), whereas exogenous ethylene slightly promoted thallus growth. STS suppressed thallus growth and induced ectopic rhizoid formation on the dorsal surface of thalli. Thus, ACC and ethylene have different effects on the vegetative growth of M. polymorpha. We generated single and double mutants of ACC synthase-like (ACSL) genes, MpACSL1 and MpACSL2. The mutants did not show obvious defects in thallus growth, ACC content and ethylene production, indicating that MpACSL genes are not essential for the vegetative growth and biosynthesis of ACC and ethylene. Gene expression analysis suggested the involvement of MpACSL1 and MpACSL2 in stress responses. Collectively, our results imply ethylene-independent function of ACC and the absence of ACC-mediated ethylene biosynthesis in M. polymorpha.

Regulation of wound ethylene biosynthesis by NAC transcription factors in kiwifruit

BACKGROUND

The phytohormone ethylene controls many processes in plant development and acts as a key signaling molecule in response to biotic and abiotic stresses: it is rapidly induced by flooding, wounding, drought, and pathogen attack as well as during abscission and fruit ripening. In kiwifruit (Actinidia spp.), fruit ripening is characterized by two distinct phases: an early phase of system-1 ethylene biosynthesis characterized by absence of autocatalytic ethylene, followed by a late burst of autocatalytic (system-2) ethylene accompanied by aroma production and further ripening. Progress has been made in understanding the transcriptional regulation of kiwifruit fruit ripening but the regulation of system-1 ethylene biosynthesis remains largely unknown. The aim of this work is to better understand the transcriptional regulation of both systems of ethylene biosynthesis in contrasting kiwifruit organs: fruit and leaves.

RESULTS

A detailed molecular study in kiwifruit (A. chinensis) revealed that ethylene biosynthesis was regulated differently between leaf and fruit after mechanical wounding. In fruit, wound ethylene biosynthesis was accompanied by transcriptional increases in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), ACC oxidase (ACO) and members of the NAC class of transcription factors (TFs). However, in kiwifruit leaves, wound-specific transcriptional increases were largely absent, despite a more rapid induction of ethylene production compared to fruit, suggesting that post-transcriptional control mechanisms in kiwifruit leaves are more important. One ACS member, AcACS1, appears to fulfil a dominant double role; controlling both fruit wound (system-1) and autocatalytic ripening (system-2) ethylene biosynthesis. In kiwifruit, transcriptional regulation of both system-1 and -2 ethylene in fruit appears to be controlled by temporal up-regulation of four NAC (NAM, ATAF1/2, CUC2) TFs (AcNAC1-4) that induce AcACS1 expression by directly binding to the AcACS1 promoter as shown using gel-shift (EMSA) and by activation of the AcACS1 promoter in planta as shown by gene activation assays combined with promoter deletion analysis.

CONCLUSIONS

Our results indicate that in kiwifruit the NAC TFs AcNAC2-4 regulate both system-1 and -2 ethylene biosynthesis in fruit during wounding and ripening through control of AcACS1 expression levels but not in leaves where post-transcriptional/translational regulatory mechanisms may prevail.

Yield, Fruit Quality, and Storability of 'Canino' Apricot in Response to Aminoethoxyvinylglycine, Salicylic Acid, and Chitosan

Ethylene plays a pivotal role in the climacteric fruit ripening and senescence process. The effect of three ethylene inhibitors on the yield, quality, and storability of ‘Canino’ apricot fruit was studied. Foliar sprays of distilled water (control), aminoethoxyvinylglycine (AVG) (150 and 100 mg·L⁻¹), salicylic acid (SA) (4 and 2 mM), and chitosan (2.5% and 1.5%) were applied 30 and 15 days before harvest. Results indicated that the high concentrations of AVG and SA recorded the lowest percentage of preharvest fruit drop and, hence, the highest yield. Trees receiving either concentration of AVG showed the highest fruit firmness. High concentrations of all three ethylene inhibitors reduced fruit weight loss, total carotenoids, and soluble solid content (SSC), but increased total acidity (TA) during cold storage (2 °C). A high score of overall taste acceptability was observed with a higher concentration of SA, which was also recorded the lowest fruit malondialdehyde content (MDA) at harvest and during storage. The highest concentrations of SA and chitosan recorded no decay for 28 days of storage. Gene expression analysis reflected higher expression of PaACS1 gene with the highest concentrations of ethylene inhibitors, suggesting that SA (4 mM) is recommended for optimal yield, quality, and storability of ‘Canino’ apricot fruit grown under Egyptian conditions.

Essential Roles of the Linker Sequence Between Tetratricopeptide Repeat Motifs of Ethylene Overproduction 1 in Ethylene Biosynthesis

Ethylene Overproduction 1 (ETO1) is a negative regulator of ethylene biosynthesis. However, the regulation mechanism of ETO1 remains largely unclear. Here, a novel eto1 allele (eto1-16) was isolated with typical triple phenotypes due to an amino acid substitution of G480C in the uncharacterized linker sequence between the TPR1 and TPR2 motifs. Further genetic and biochemical experiments confirmed the eto1-16 mutation site. Sequence analysis revealed that G480 is conserved not only in two paralogs, EOL1 and EOL2, in Arabidopsis, but also in the homologous protein in other species. The glycine mutations (eto1-11, eto1-12, and eto1-16) do not influence the mRNA abundance of ETO1, which is reflected by the mRNA secondary structure similar to that of WT. According to the protein-protein interaction analysis, the abnormal root phenotype of eto1-16 might be caused by the disruption of the interaction with type 2 1-aminocyclopropane-1-carboxylic acid (ACC) synthases (ACSs) proteins. Overall, these data suggest that the linker sequence between tetratricopeptide repeat (TPR) motifs and the glycine in TPR motifs or the linker region are essential for ETO1 to bind with downstream mediators, which strengthens our knowledge of ETO1 regulation in balancing ACSs.

Unravelling Differences in Candidate Genes for Drought Tolerance in Potato (Solanum tuberosum L.) by Use of New Functional Microsatellite Markers

Potato is regarded as drought sensitive and most vulnerable to climate changes. Its cultivation in drought prone regions or under conditions of more frequent drought periods, especially in subtropical areas, requires intensive research to improve drought tolerance in order to guarantee high yields under limited water supplies. A candidate gene approach was used to develop functional simple sequence repeat (SSR) markers for association studies in potato with the aim to enhance breeding for drought tolerance. SSR primer combinations, mostly surrounding interrupted complex and compound repeats, were derived from 103 candidate genes for drought tolerance. Validation of the SSRs was performed in an association panel representing 34 mainly starch potato cultivars. Seventy-five out of 154 SSR primer combinations (49%) resulted in polymorphic, highly reproducible banding patterns with polymorphic information content (PIC) values between 0.11 and 0.90. Five SSR markers identified allelic differences between the potato cultivars that showed significant associations with drought sensitivity. In all cases, the group of drought-sensitive cultivars showed predominantly an additional allele, indicating that selection against these alleles by marker-assisted breeding might confer drought tolerance. Further studies of these differences in the candidate genes will elucidate their role for an improved performance of potatoes under water-limited conditions.

l-Aspartate: An Essential Metabolite for Plant Growth and Stress Acclimation

L-aspartate (Asp) serves as a central building block, in addition to being a constituent of proteins, for many metabolic processes in most organisms, such as biosynthesis of other amino acids, nucleotides, nicotinamide adenine dinucleotide (NAD), the tricarboxylic acid (TCA) cycle and glycolysis pathway intermediates, and hormones, which are vital for growth and defense. In animals and humans, lines of data have proved that Asp is indispensable for cell proliferation. However, in plants, despite the extensive study of the Asp family amino acid pathway, little attention has been paid to the function of Asp through the other numerous pathways. This review aims to elucidate the most important aspects of Asp in plants, from biosynthesis to catabolism and the role of Asp and its metabolic derivatives in response to changing environmental conditions. It considers the distribution of Asp in various cell compartments and the change of Asp level, and its significance in the whole plant under various stresses. Moreover, it provides evidence of the interconnection between Asp and phytohormones, which have prominent functions in plant growth, development, and defense. The updated information will help improve our understanding of the physiological role of Asp and Asp-borne metabolic fluxes, supporting the modular operation of these networks.

The Sequential Action of MIDA9/PP2C.D1, PP2C.D2, and PP2C.D5 Is Necessary to Form and Maintain the Hook After Germination in the Dark

During seedling etiolation after germination in the dark, seedlings have closed cotyledons and form an apical hook to protect the meristem as they break through the soil to reach the surface. Once in contact with light, the hook opens and cotyledons are oriented upward and separate. Hook development in the dark after seedling emergence from the seed follows three distinctly timed and sequential phases: formation, maintenance, and eventual opening. We previously identified MISREGULATED IN DARK9 (MIDA9) as a phytochrome interacting factor (PIF)-repressed gene in the dark necessary for hook development during etiolated growth. MIDA9 encodes the type 2C phosphatase PP2C.D1, and pp2c-d1/mida9 mutants exhibit open hooks in the dark. Recent evidence has described that PP2C.D1 and other PP2C.D members negatively regulate SMALL AUXIN UP RNA (SAUR)-mediated cell elongation. However, the fundamental question of the timing of PP2C.D1 action (and possibly other members of the PP2C.D family) during hook development remains to be addressed. Here, we show that PP2C.D1 is required immediately after germination to form the hook. pp2c.d1/mida9 shows reduced cell expansion in the outer layer of the hook and, therefore, does not establish the differential cell growth necessary for hook formation, indicating that PP2C.D1 is necessary to promote cell elongation during this early stage. Additionally, genetic analyses of single and high order mutants in PP2C.D1, PP2C.D2, and PP2C.D5 demonstrate that the three PP2C.Ds act collectively and sequentially during etiolation: whereas PP2C.D1 dominates hook formation, PP2C.D2 is necessary during the maintenance phase, and PP2C.D5 acts to prevent opening during the third phase together with PP2C.D1 and PP2C.D2. Finally, we uncover a possible connection of PP2C.D1 levels with ethylene physiology, which could help optimize hook formation during post-germinative growth in the dark.

UV RESISTANCE LOCUS8 mediates ultraviolet-B-induced stomatal closure in an ethylene-dependent manner

Although the UV RESISTANCE LOCUS 8 (UVR8)-CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)-ELONGATED HYPOCOTYL5 (HY5) signaling pathway, ethylene, hydrogen peroxide (H₂O₂), and nitric oxide (NO) all participate in ultraviolet-B (UV-B)-triggered stomatal closing, their interrelationship is not clear. Here, we found that UV-B-induced the expression of ethylene biosynthetic genes, production of ethylene, H₂O₂, and NO, and stomata closing were impaired in uvr8, cop1, and hy5 mutants. UV-B-induced NO production and stomata closing were also defective in mutants for ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), and EIN3, but UV-B-triggered H₂O₂ generation was only inhibited in etr1. In either the absence or presence of UV-B, ethylene triggered H₂O₂ production but not NO generation and stomatal closure in cop1 and hy5, and stomata closing in cop1 and hy5 was induced by NO but not H₂O₂. Moreover, NO production and stomatal closure were constitutively caused by over-expression of COP1 or HY5 in ein2 and ein3, but not by over-expression of EIN2 or EIN3 in cop1 and hy5. Our data indicate that the UVR8-COP1-HY5 signaling module mediates UV-B-induced ethylene production, ethylene is then perceived by ETR1 to induce H₂O₂ synthesis. H₂O₂ induces NO generation and subsequent stomata closing via an EIN2, EIN3, COP1, and HY5-dependent pathway(s).

Insights into the genes involved in the ethylene biosynthesis pathway in Arabidopsis thaliana and Oryza sativa

Background

Ethylene is a gaseous plant hormone that acts as a requisite role in many aspects of the plant life cycle, and it is also a regulator of plant responses to abiotic and biotic stresses. In this study, we attempt to provide comprehensive information through analyses of existing data using bioinformatics tools to compare the identified ethylene biosynthesis genes between Arabidopsis (as dicotyledonous) and rice (as monocotyledonous).

Results

The results exposed that the Arabidopsis proteins of the ethylene biosynthesis pathway had more potential glycosylation sites than rice, and 1-aminocyclopropane-1-carboxylate oxidase proteins were less phosphorylated than 1-aminocyclopropane-1-carboxylate synthase and S-adenosylmethionine proteins. According to the gene expression patterns, S-adenosylmethionine genes were more involved in the rice-ripening stage while in Arabidopsis, ACS2, and 1-aminocyclopropane-1-carboxylate oxidase genes were contributed to seed maturity. Furthermore, the result of miRNA targeting the transcript sequences showed that ath-miR843 and osa-miR1858 play a key role to regulate the post-transcription modification of S-adenosylmethionine genes in Arabidopsis and rice, respectively. The discovered cis- motifs in the promoter site of all the ethylene biosynthesis genes of A. thaliana genes were engaged to light-induced response in the cotyledon and root genes, sulfur-responsive element, dehydration, cell cycle phase-independent activation, and salicylic acid. The ACS4 protein prediction demonstrated strong protein-protein interaction in Arabidopsis, as well as, SAM2, Os04T0578000, Os01T0192900, and Os03T0727600 predicted strong protein-protein interactions in rice.

Conclusion

In the current study, the complex between miRNAs with transcript sequences of ethylene biosynthesis genes in A. thaliana and O. sativa were identified, which could be helpful to understand the gene expression regulation after the transcription process. The binding sites of common transcription factors such as MYB, WRKY, and ABRE that control target genes in abiotic and biotic stresses were generally distributed in promoter sites of ethylene biosynthesis genes of A. thaliana. This was the first time to wide explore the ethylene biosynthesis pathway using bioinformatics tools that markedly showed the capability of the in silico study to integrate existing data and knowledge and furnish novel insights into the understanding of underlying ethylene biosynthesis pathway genes that will be helpful for more dissection.

The genetic framework of shoot regeneration in Arabidopsis comprises master regulators and conditional fine-tuning factors

Clonal propagation and genetic engineering of plants requires regeneration, but many species are recalcitrant and there is large variability in explant responses. Here, we perform a genome-wide association study using 190 natural Arabidopsis accessions to dissect the genetics of shoot regeneration from root explants and several related in vitro traits. Strong variation is found in the recorded phenotypes and association mapping pinpoints a myriad of quantitative trait genes, including prior candidates and potential novel regeneration determinants. As most of these genes are trait- and protocol-specific, we propose a model wherein shoot regeneration is governed by many conditional fine-tuning factors and a few universal master regulators such as WUSCHEL, whose transcript levels correlate with natural variation in regenerated shoot numbers. Potentially novel genes in this last category are AT3G09925, SUP, EDA40 and DOF4.4. We urge future research in the field to consider multiple conditions and genetic backgrounds.

Robin Lardon et al. report a genome-wide association study of shoot regeneration in Arabidopsis under 2 different in vitro incubation conditions. They find wide variation in regeneration phenotypes, attributable to allelic variants in key developmental genes, and show that genetic association patterns differ depending on environmental factors.

No Home without Hormones: How Plant Hormones Control Legume Nodule Organogenesis

The establishment of symbiotic nitrogen fixation requires the coordination of both nodule development and infection events. Despite the evolution of a variety of anatomical structures, nodule organs serve a common purpose in establishing a localized area that facilitates efficient nitrogen fixation. As in all plant developmental processes, the establishment of a new nodule organ is regulated by plant hormones. During nodule initiation, regulation of plant hormone signaling is one of the major targets of symbiotic signaling. We review the role of major developmental hormones in the initiation of the nodule organ and argue that the manipulation of plant hormones is a key requirement for engineering nitrogen fixation in non-legumes as the basis for improved food security and sustainability.

Two glyoxylate reductase isoforms are functionally redundant but required under high photorespiration conditions in rice

BACKGROUND

The glyoxylate reductase (GR) multigene family has been described in various plant species, their isoforms show different biochemical features in plants. However, few studies have addressed the biological roles of GR isozymes, especially for rice.

RESULTS

Here, we report a detailed analysis of the enzymatic properties and physiological roles of OsGR1 and OsGR2 in rice. The results showed that both enzymes prefer NADPH to NADH as cofactor, and the NADPH-dependent glyoxylate reducing activity represents the major GR activity in various tissues and at different growth stages; and OsGR1 proteins were more abundant than OsGR2, which is also a major contributor to total GR activities. By generating and characterizing various OsGR-genetically modified rice lines, including overexpression, single and double-knockout lines, we found that no phenotypic differences occur among the various transgenic lines under normal growth conditions, while a dwarfish growth phenotype was noticed under photorespiration-promoted conditions.

CONCLUSION

Our results suggest that OsGR1 and OsGR2, with distinct enzymatic characteristics, function redundantly in detoxifying glyoxylate in rice plants under normal growth conditions, whereas both are simultaneously required under high photorespiration conditions.

Ethylene mediates salicylic-acid-induced stomatal closure by controlling reactive oxygen species and nitric oxide production in Arabidopsis

Both salicylic acid (SA) and ethylene induce stomatal closure and positively regulate stomatal immunity, but their interactions in guard cell signaling are unclear. Here, we observed that SA induced the expression of ethylene biosynthetic genes; the production of ethylene, reactive oxygen species (ROS) and nitric oxide (NO); and stomatal closure in Arabidopsis thaliana. However, SA-induced stomatal closure was inhibited by an ethylene biosynthetic inhibitor and mutations in ethylene biosynthetic genes, ethylene-signaling genes [RESPONSE TO ANTAGONIST 1 (RAN1), ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), EIN3 and ARABIDOPSIS RESPONSE REGULATOR 2 (ARR2)], NADPH oxidase genes [ATRBOHD and ATRBOHF], and nitrate reductase genes (NIA1 and NIA2). Furthermore, SA-triggered ROS production in guard cells was impaired in ran1, etr1, AtrbohD and AtrbohF, but not in ein2, ein3 or arr2. SA-triggered NO production was impaired in all ethylene-signaling mutants tested and in nia1 and nia2. The stomata of mutants for CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) showed constitutive ROS and NO production and closure. These results indicate that ethylene mediates SA-induced stomatal closure by activating ATRBOHD/F-mediated ROS synthesis in an RAN1-, ETR1- and CTR1-dependent manner. This in turn induces NIA1/2-mediated NO production and subsequent stomatal closure via the ETR1, EIN2, EIN3 and ARR2-dependent pathway(s).

Hormonal regulation of root hair growth and responses to the environment in Arabidopsis

The main functions of plant roots are water and nutrient uptake, soil anchorage, and interaction with soil-living biota. Root hairs, single cell tubular extensions of root epidermal cells, facilitate or enhance these functions by drastically enlarging the absorptive surface. Root hair development is constantly adapted to changes in the root's surroundings, allowing for optimization of root functionality in heterogeneous soil environments. The underlying molecular pathway is the result of a complex interplay between position-dependent signalling and feedback loops. Phytohormone signalling interconnects this root hair signalling cascade with biotic and abiotic changes in the rhizosphere, enabling dynamic hormone-driven changes in root hair growth, density, length, and morphology. This review critically discusses the influence of the major plant hormones on root hair development, and how changes in rhizosphere properties impact on the latter.

Protein Phosphatases Type 2C Group A Interact with and Regulate the Stability of ACC Synthase 7 in Arabidopsis

Ethylene is an important plant hormone that controls growth, development, aging and stress responses. The rate-limiting enzymes in ethylene biosynthesis, the 1-aminocyclopropane-1-carboxylate synthases (ACSs), are strictly regulated at many levels, including posttranslational control of protein half-life. Reversible phosphorylation/dephosphorylation events play a pivotal role as signals for ubiquitin-dependent degradation. We showed previously that ABI1, a group A protein phosphatase type 2C (PP2C) and a key negative regulator of abscisic acid signaling regulates type I ACS stability. Here we provide evidence that ABI1 also contributes to the regulation of ethylene biosynthesis via ACS7, a type III ACS without known regulatory domains. Using various approaches, we show that ACS7 interacts with ABI1, ABI2 and HAB1. We use molecular modeling to predict the amino acid residues involved in ABI1/ACS7 complex formation and confirm these predictions by mcBiFC–FRET–FLIM analysis. Using a cell-free degradation assay, we show that proteasomal degradation of ACS7 is delayed in protein extracts prepared from PP2C type A knockout plants, compared to a wild-type extract. This study therefore shows that ACS7 undergoes complex regulation governed by ABI1, ABI2 and HAB1. Furthermore, this suggests that ACS7, together with PP2Cs, plays an essential role in maintaining appropriate levels of ethylene in Arabidopsis.