Genome-wide analysis of the cotton G-coupled receptor proteins (GPCR) and functional analysis of GTOM1, a novel cotton GPCR gene under drought and cold stress

Proteome-wide analysis reveals G protein-coupled receptor-like proteins in rice (Oryza sativa)

G protein-coupled receptors (GPCRs) constitute the largest family of transmembrane proteins in metazoans that mediate the regulation of various physiological responses to discrete ligands through heterotrimeric G protein subunits. The existence of GPCRs in plant is contentious, but their comparable crucial role in various signaling pathways necessitates the identification of novel remote GPCR-like proteins that essentially interact with the plant G protein α subunit and facilitate the transduction of various stimuli. In this study, we identified three putative GPCR-like proteins (OsGPCRLPs) (LOC_Os06g09930.1, LOC_Os04g36630.1, and LOC_Os01g54784.1) in the rice proteome using a stringent bioinformatics workflow. The identified OsGPCRLPs exhibited a canonical GPCR 'type I' 7TM topology, patterns, and biologically significant sites for membrane anchorage and desensitization. Cluster-based interactome mapping revealed that the identified proteins interact with the G protein α subunit which is a characteristic feature of GPCRs. Computational results showing the interaction of identified GPCR-like proteins with G protein α subunit and its further validation by the membrane yeast-two-hybrid assay strongly suggest the presence of GPCR-like 7TM proteins in the rice proteome. The absence of a regulator of G protein signaling (RGS) box in the C- terminal domain, and the presence of signature motifs of canonical GPCR in the identified OsGPCRLPs strongly suggest that the rice proteome contains GPCR-like proteins that might be involved in signal transduction.

Pivotal role of heterotrimeric G protein in the crosstalk between sugar signaling and abiotic stress response in plants

Heterotrimeric G-proteins are key modulators of multiple signaling and developmental pathways in plants, in which they act as molecular switches to engage in transmitting various stimuli signals from outside into the cells. Substantial studies have identified G proteins as essential components of the organismal response to abiotic stress, leading to adaptation and survival in plants. Meanwhile, sugars are also well acknowledged key players in stress perception, signaling, and gene expression regulation. Connections between the two significant signaling pathways in stress response are of interest to a general audience in plant biology. In this article, advances unraveling a pivotal role of G proteins in the process of sugar signals outside the cells being translated into the operation of autophagy in cells during stress are reviewed. In addition, we have presented recent findings on G proteins regulating the response to drought, salt, alkali, cold, heat and other abiotic stresses. Perspectives on G-protein research are also provided in the end. Since G protein signaling regulates many agronomic traits, elucidation of detailed mechanism of the related pathways would provide useful insights for the breeding of abiotic stress resistant and high-yield crops.

Genome-wide association analysis identified molecular markers and candidate genes for flower traits in Chinese orchid (Cymbidium sinense)

The orchid, the champagne of flowers, brings luxury, elegance, and novelty to nature. Cymbidium sinense is a symbol of gigantic floral variability on account of wavering shapes and sizes of floral organs, although marker-trait association (MTA) has not been studied for its floral traits. We evaluated markers associated with 14 floral traits of C. sinense through a genome-wide association study (GWAS) of 195 accessions. A total of 65 318 522 single-nucleotide polymorphisms (SNPs) and 3 906 176 insertion/deletion (InDel) events were identified through genotyping-by-sequencing. Among these, 4694 potential SNPs and 477 InDels were identified as MTAs at -log10 P > 5. The genes related to these SNPs and InDels were largely associated with floral regulators, hormonal pathways, cell division, and metabolism, playing essential roles in tailoring floral morphology. Moreover, 20 candidate SNPs/InDels linked to 11 genes were verified, 8 of which were situated on exons, one was located in the 5'-UTR and two were positioned in introns. Here, the multitepal trait-related gene RABBIT EARS (RBE) was found to be the most crucial gene. We analyzed the role of CsRBE in the regulation of flower-related genes via efficient transient overexpression in C. sinense protoplasts, and found that the floral homeotic genes CsAP3 and CsPI, as well as organ boundary regulators, including CsCUC and CsTCP genes, were regulated by CsRBE. Thus, we obtained key gene loci for important ornamental traits of orchids using genome-wide association analysis of populations with natural variation. The findings of this study can do a great deal to expedite orchid breeding programs for shape variability.

In silico structural-functional characterization of three differentially expressed resistance gene analogs identified in Dalbergia sissoo against dieback disease reveals their role in immune response regulation

Plant immunity includes enemy recognition, signal transduction, and defensive response against pathogens. We experimented to identify the genes that contribute resistance against dieback disease to Dalbergia sissoo, an economically important timber tree. In this study, we investigated the role of three differentially expressed genes identified in the dieback-induced transcriptome in Dalbergia sissoo. The transcriptome was probed using DOP-rtPCR analysis. The identified RGAs were characterized in silico as the contributors of disease resistance that switch on under dieback stress. Their predicted fingerprints revealed involvement in stress response. Ds-DbRCaG-02-Rga.a, Ds-DbRCaG-04-Rga.b, and Ds-DbRCaG-06-Rga.c showed structural homology with the Transthyretin-52 domain, EAL associated YkuI_C domain, and Src homology-3 domain respectively, which are the attributes of signaling proteins possessing a role in regulating immune responses in plants. Based on in-silico structural and functional characterization, they were predicted to have a role in immune response regulation in D. sissoo.

The resilient cotton plant: uncovering the effects of stresses on secondary metabolomics and its underlying molecular mechanisms

Cotton is an important fiber crop cultivated around the world under diverse climate conditions and generates billions of dollars in annual revenue globally. Biotic and abiotic stresses have caused reduction in yield and productivity of cotton crops. In this review, we comprehensively analyzed and summarized the effect of biotic and abiotic stress on secondary metabolite production in cotton. The development of cotton varieties with improved tolerance against abiotic and biotic stress can play an important role in sustainable cotton production. Under stress conditions, plants develop a variety of defense mechanisms such as initiating signaling functions to upregulate defense responsive genes and accumulation of secondary metabolites. Understanding the impact of stress on secondary metabolite production in cotton is crucial for developing strategies to alleviate the negative effects of stress on crop yield and quality. Further, the potential industrial applications of these secondary metabolites in cotton, such as gossypol, could provide new opportunities for sustainable cotton production and the development of value-added products. Additionally, transgenic and genome-edited cotton cultivars can be developed to provide tolerance to both abiotic and biotic stress in cotton production.

Genome-wide association study identifies GhSAL1 affects cold tolerance at the seedling emergence stage in upland cotton (Gossypium hirsutum L.)

Genomic analysis of upland cotton revealed that cold tolerance was associated with ecological distribution. GhSAL1 on chromosome D09 negatively regulated cold tolerance of upland cotton. Cotton can undergo low-temperature stress at the seedling emergence stage, which adversely affects growth and yield; however, the regulatory mechanism underlying cold tolerance remains nebulous. Here, we analyze the phenotypic and physiological parameters in 200 accessions from 5 ecological distributions under constant chilling (CC) and diurnal variation of chilling (DVC) stresses at the seedling emergence stage. All accessions were clustered into four groups, of which Group IV, with most germplasms from the northwest inland region (NIR), had better phenotypes than Groups I-III under the two kinds of chilling stresses. A total of 575 significantly associated single-nucleotide polymorphism (SNP) were identified, and 35 stable genetic quantitative trait loci (QTL) were obtained, of which 5 were associated with traits under CC and DVC stress, respectively, while the remaining 25 were co-associated. The accumulation of dry weight (DW) of seedling was associated with the flavonoid biosynthesis process regulated by Gh_A10G0500. The emergence rate (ER), DW, and total length of seedling (TL) under CC stress were associated with the SNPs variation of Gh_D09G0189 (GhSAL1). GhSAL1^HapB was the elite haplotype, which increased ER, DW, and TL by 19.04%, 11.26%, and 7.69%, respectively, compared with that of GhSAL1^HapA. The results of virus-induced gene silencing (VIGS) experiment and determination of metabolic substrate content preliminarily illustrated that GhSAL1 negatively regulated cotton cold tolerance through IP₃-Ca²⁺ signaling pathway. The elite haplotypes and candidate genes identified in this study could be used to improve cold tolerance at the seedling emergence stage in future upland cotton breeding.

Life, death and resurrection of plant GPCRs

The activation of G-protein coupled receptors (GPCRs) by extracellular ligands constitutes the first step of heterotrimeric G-protein signalling in animals. In plants, canonical GPCRs have been known for over 25 years, often in association with agronomically important functions. But their role in plant G-protein signalling and even their annotation as GPCR was contested in the last decade, only to be revisited in the light of more recent evidences. In this first ever review on plant GPCRs, we catalogue all the plant GPCRs described to date and discuss the evidences for and against their role in plants in general and G-protein signalling in particular. We argue against writing off GPCRs and point to the missing links to be investigated to establish firm conclusions either way.

Combined transcriptome and metabolome analysis revealed pathways involved in improved salt tolerance of Gossypium hirsutum L. seedlings in response to exogenous melatonin application

BACKGROUND

Salinization is major abiotic stress limiting cotton production. Melatonin (MT) has been implicated in salt stress tolerance in multiple crops including upland cotton. Here, we explored the transcriptomic and metabolomic response of a salt-tolerant self-bred high-yielding cotton line SDS-01, which was exogenously sprayed with four MT concentrations (50, 100, 200, and 500 μM).

RESULTS

Here we found that MT improves plant biomass and growth under salt stress. The combined transcriptome sequencing and metabolome profiling approach revealed that photosynthetic efficiency is improved by increasing the expressions of chlorophyll metabolism and antenna proteins in MT-treated seedlings. Additionally, linoleic acid and flavonoid biosynthesis were improved after MT treatment. The Na+/K+ homeostasis-related genes were increasingly expressed in salt-stressed seedlings treated with MT as compared to the ones experiencing only salt stress. Melatonin treatment activated a cascade of plant-hormone signal transduction and reactive oxygen scavenging genes to alleviate the detrimental effects of salt stress. The global metabolome profile revealed an increased accumulation of flavonoids, organic acids, amino acids and derivatives, saccharides, and phenolic acids in MT-treated seedlings. Interestingly, N, N'-Diferuloylputrescine a known antioxidative compound was highly accumulated after MT treatment.

CONCLUSION

Collectively, our study concludes that MT is a salt stress regulator in upland cotton and alleviates salt-stress effects by modulating the expressions of photosynthesis (and related pathways), flavonoid, ROS scavenging, hormone signaling, linoleic acid metabolism, and ion homeostasis-related genes.

Identification of resistance gene analogs of the NBS-LRR family through transcriptome probing and in silico prediction of the expressome of Dalbergia sissoo under dieback disease stress

Dalbergia sissoo is an important timber tree, and dieback disease poses a dire threat to it toward extinction. The genomic record of D. sissoo is not available yet on any database; that is why it is challenging to probe the genetic elements involved in stress resistance. Hence, we attempted to unlock the genetics involved in dieback resistance through probing the NBS-LRR family, linked with mostly disease resistance in plants. We analyzed the transcriptome of D. sissoo under dieback challenge through DOP-rtPCR analysis using degenerate primers from conserved regions of NBS domain-encoded gene sequences. The differentially expressed gene sequences were sequenced and in silico characterized for predicting the expressome that contributes resistance to D. sissoo against dieback. The molecular and bioinformatic analyses predicted the presence of motifs including ATP/GTP-binding site motif A (P-loop NTPase domain), GLPL domain, casein kinase II phosphorylation site, and N-myristoylation site that are the attributes of proteins encoded by disease resistance genes. The physicochemical characteristics of identified resistance gene analogs, subcellular localization, predicted protein fingerprints, in silico functional annotation, and predicted protein structure proved their role in disease and stress resistance.

Fungal and bacterial oxylipins are signals for intra- and inter-cellular communication within plant disease

Lipids are central at various stages of host-pathogen interactions in determining virulence and modulating plant defense. Free fatty acids may act as substrates for oxidizing enzymes [e.g., lipoxygenases (LOXs) and dioxygenases (DOXs)] that synthesize oxylipins. Fatty acids and oxylipins function as modulators of several pathways in cell-to-cell communication; their structural similarity among plant, fungal, and bacterial taxa suggests potential in cross-kingdom communication. We provide a prospect of the known role of fatty acids and oxylipins in fungi and bacteria during plant-pathogen interactions. In the pathogens, oxylipin-mediated signaling pathways are crucial both in development and host infection. Here, we report on case studies suggesting that oxylipins derived from oleic, linoleic, and linolenic acids are crucial in modulating the pathogenic lifestyle in the host plant. Intriguingly, overlapping (fungi-plant/bacteria-plant) results suggest that different inter-kingdom pathosystems use similar lipid signals to reshape the lifestyle of the contenders and occasionally determine the outcome of the challenge.

Identification of Candidate Genes Regulating Drought Tolerance in Pearl Millet

Pearl millet is an important crop of the arid and semi-arid ecologies to sustain food and fodder production. The greater tolerance to drought stress attracts us to examine its cellular and molecular mechanisms via functional genomics approaches to augment the grain yield. Here, we studied the drought response of 48 inbreds representing four different maturity groups at the flowering stage. A set of 74 drought-responsive genes were separated into five major phylogenic groups belonging to eight functional groups, namely ABA signaling, hormone signaling, ion and osmotic homeostasis, TF-mediated regulation, molecular adaptation, signal transduction, physiological adaptation, detoxification, which were comprehensively studied. Among the conserved motifs of the drought-responsive genes, the protein kinases and MYB domain proteins were the most conserved ones. Comparative in-silico analysis of the drought genes across millet crops showed foxtail millet had most orthologs with pearl millet. Of 698 haplotypes identified across millet crops, MyC2 and Myb4 had maximum haplotypes. The protein–protein interaction network identified ABI2, P5CS, CDPK, DREB, MYB, and CYP707A3 as major hub genes. The expression assay showed the presence of common as well as unique drought-responsive genes across maturity groups. Drought tolerant genotypes in respective maturity groups were identified from the expression pattern of genes. Among several gene families, ABA signaling, TFs, and signaling proteins were the prospective contributors to drought tolerance across maturity groups. The functionally validated genes could be used as promising candidates in backcross breeding, genomic selection, and gene-editing schemes in pearl millet and other millet crops to increase the yield in drought-prone arid and semi-arid ecologies.

Antioxidant Regulation and DNA Methylation Dynamics During Mikania micrantha Seed Germination Under Cold Stress

As a primary goal, adaptation to cold climate could expand an invasion range of exotic plants. Here, we aimed to explore the regulation strategy of M. micrantha seed development under cold stress through molecular physiology and multi-omics analysis. Significant increase of hydrogen peroxide, malondialdehyde, and electrolyte leakage observed under cold stress revealed that oxidative damage within M. micrantha seed cells was induced in the initial germination phase. Proteomic data underscored an activation of antioxidant activity to maintain redox homeostasis, with a cluster of antioxidant proteins identified. Genomic-wide transcriptome, in combination with time-series whole-genome bisulfite sequencing mining, elucidated that seven candidate genes, which were the target of DNA demethylation-dependent ROS scavenging, were possibly associated with an M. micrantha germ break. Progressive gain of CHH context DNA methylation identified in an early germination phrase suggested a role of a DNA methylation pathway, while an active DNA demethylation pathway was also initiated during late seed development, which was in line with the expression trend of methylation and demethylation-related genes verified through qRT-PCR. These data pointed out that cold-dependent DNA demethylation and an antioxidant regulatory were involved together in restoring seed germination. The expression level of total 441 genes presented an opposite trend to the methylation divergence, while the expression of total 395 genes was proved to be negatively associated with their methylation levels. These data provided new insights into molecular reprograming events during M. micrantha seed development.

A Sugarcane G-Protein-Coupled Receptor, ShGPCR1, Confers Tolerance to Multiple Abiotic Stresses

Sugarcane (Saccharum spp.) is a prominent source of sugar and serves as bioenergy/biomass feedstock globally. Multiple biotic and abiotic stresses, including drought, salinity, and cold, adversely affect sugarcane yield. G-protein-coupled receptors (GPCRs) are components of G-protein-mediated signaling affecting plant growth, development, and stress responses. Here, we identified a GPCR-like protein (ShGPCR1) from sugarcane and energy cane (Saccharum spp. hybrids) and characterized its function in conferring tolerance to multiple abiotic stresses. ShGPCR1 protein sequence contained nine predicted transmembrane (TM) domains connected by four extracellular and four intracellular loops, which could interact with various ligands and heterotrimeric G proteins in the cells. ShGPCR1 sequence displayed other signature features of a GPCR, such as a putative guanidine triphosphate (GTP)-binding domain, as well as multiple myristoylation and protein phosphorylation sites, presumably important for its biochemical function. Expression of ShGPCR1 was upregulated by drought, salinity, and cold stresses. Subcellular imaging and calcium (Ca²⁺) measurements revealed that ShGPCR1 predominantly localized to the plasma membrane and enhanced intracellular Ca²⁺ levels in response to GTP, respectively. Furthermore, constitutive overexpression of ShGPCR1 in sugarcane conferred tolerance to the three stressors. The stress-tolerance phenotype of the transgenic lines corresponded with activation of multiple drought-, salinity-, and cold-stress marker genes, such as Saccharum spp. LATE EMBRYOGENESIS ABUNDANT, DEHYDRIN, DROUGHT RESPONSIVE 4, GALACTINOL SYNTHASE, ETHYLENE RESPONSIVE FACTOR 3, SALT OVERLY SENSITIVE 1, VACUOLAR Na+/H+ ANTIPORTER 1, NAM/ATAF1/2/CUC2, COLD RESPONSIVE FACTOR 2, and ALCOHOL DEHYDROGENASE 3. We suggest that ShGPCR1 plays a key role in conferring tolerance to multiple abiotic stresses, and the engineered lines may be useful to enhance sugarcane production in marginal environments with fewer resources.

Carrot AOX2a Transcript Profile Responds to Growth and Chilling Exposure

Alternative oxidase (AOX) is a key enzyme of the alternative respiration, known to be involved in plant development and in response to various stresses. To verify the role of DcAOX1 and DcAOX2a genes in carrot tap root growth and in response to cold stress, their expression was analyzed in two experiments: during root growth for 13 weeks and in response to a cold challenge trial of 7 days, in both cases using different carrot cultivars. Carrot root growth is initially characterized by an increase in length, followed by a strong increase in weight. DcAOX2a presented the highest expression levels during the initial stages of root growth for all cultivars, but DcAOX1 showed no particular trend in expression. Cold stress had a negative impact on root growth, and generally up-regulated DcAOX2a with no consistent effect on DcAOX1. The identification of cis-acting regulatory elements (CAREs) located at the promoters of both genes showed putative sequences involved in cold stress responsiveness, as well as growth. However, DcAOX2a promoter presented more CAREs related to hormonal pathways, including abscisic acid and gibberellins synthesis, than DcAOX1. These results point to a dual role of DcAOX2a on carrot tap root secondary growth and cold stress response.

Research Advances in Heterotrimeric G-Protein α Subunits and Uncanonical G-Protein Coupled Receptors in Plants

As crucial signal transducers, G-proteins and G-protein-coupled receptors (GPCRs) have attracted increasing attention in the field of signal transduction. Research on G-proteins and GPCRs has mainly focused on animals, while research on plants is relatively rare. The mode of action of G-proteins is quite different from that in animals. The G-protein α (Gα) subunit is the most essential member of the G-protein signal cycle in animals and plants. The G-protein is activated when Gα releases GDP and binds to GTP, and the relationships with the GPCR and the downstream signal are also achieved by Gα coupling. It is important to study the role of Gα in the signaling pathway to explore the regulatory mechanism of G-proteins. The existence of a self-activated Gα in plants makes it unnecessary for the canonical GPCR to activate the G-protein by exchanging GDP with GTP. However, putative GPCRs have been found and proven to play important roles in G-protein signal transduction. The unique mode of action of G-proteins and the function of putative GPCRs in plants suggest that the same definition used in animal research cannot be used to study uncanonical GPCRs in plants. This review focuses on the different functions of the Gα and the mode of action between plants and animals as well as the functions of the uncanonical GPCR. This review employs a new perspective to define uncanonical GPCRs in plants and emphasizes the role of uncanonical GPCRs and Gα subunits in plant stress resistance and agricultural production.

Genome-Wide Study of NOT2_3_5 Protein Subfamily in Cotton and Their Necessity in Resistance to Verticillium wilt

The Negative on TATA-less (NOT) 2_3_5 domain proteins play key roles in mRNA metabolism and transcription regulation, but few comprehensive studies have focused on this protein family in plants. In our study, a total of 30 NOT2_3_5 genes were identified in four cotton genomes: Gossypium. arboretum, G. raimondii, G. hirsutum and G. barbadense. Phylogenetic analysis showed that all the NOT2_3_5 domain proteins were divided into two classes. The NOT2_3_5 genes were expanded frequently, and segmental duplication had significant effects in their expansion process. The cis-regulatory elements analysis of NOT2_3_5 promoter regions indicated that NOT2_3_5 domain proteins might participate in plant growth and development processes and responds to exogenous stimuli. Expression patterns demonstrated that all of the GhNOT2_3_5 genes were expressed in the majority of tissues and fiber development stages, and that these genes were induced by multiple stresses. Quantitative real-time PCR showed that GbNOT2_3_5 genes were up-regulated in response to verticillium wilt and the silencing of GbNOT2_3_5-3/8 and GbNOT2_3_5-4/9 led to more susceptibility to verticillium wilt than controls. Identification and analysis of the NOT2_3_5 protein family will be beneficial for further research on their biological functions.

Overexpression of GhMPK3 from Cotton Enhances Cold, Drought, and Salt Stress in Arabidopsis

Cotton production is hampered by a variety of abiotic stresses that wreak havoc on the growth and development of plants, resulting in significant financial losses. According to reports, cotton production areas have declined around the world as a result of the ongoing stress. Therefore, plant breeding programs are concentrating on abiotic stress-tolerant cotton varieties. Mitogen-activated protein kinase (MAPK) cascades are involved in plant growth, stress responses, and the hormonal signaling pathway. In this research, three abiotic stresses (cold, drought, and salt) were analyzed on GhMPK3 transformed Arabidopsis plants. The transgenic plant’s gene expression and morphologic analysis were studied under cold, drought, and salt stress. Physiological parameters such as relative leaf water content, excised leaf water loss, chlorophyll content, and ion leakage showed that overexpressed plants possess more stable content under stress conditions compared with the WT plants. Furthermore, GhMPK3 overexpressed plants had greater antioxidant activities and weaker oxidant activities. Silencing GhMPK3 in cotton inhibited its tolerance to drought stress. Our research findings strongly suggest that GhMPK3 can be regarded as an essential gene for abiotic stress tolerance in cotton plants.

Comparative Transcriptome Analysis Provides Insights into the Seed Germination in Cotton in Response to Chilling Stress

Gossypium hirsutum L., is a widely cultivated cotton species around the world, but its production is seriously threatened by its susceptibility to chilling stress. Low temperature affects its germination, and the underlying molecular mechanisms are rarely known, particularly from a transcriptional perspective. In this study, transcriptomic profiles were analyzed and compared between two cotton varieties, the cold-tolerant variety KN27-3 and susceptible variety XLZ38. A total of 7535 differentially expressed genes (DEGs) were identified. Among them, the transcripts involved in energy metabolism were significantly enriched during germination based on analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, such as glycolysis/gluconeogenesis, tricarboxylic acid cycle (TCA cycle), and glyoxylate cycle (GAC). Results from further GO enrichment analysis show the earlier appearance of DNA integration, meristem growth, cotyledon morphogenesis, and other biological processes in KN27-3 compared with XLZ38 under chilling conditions. The synthesis of asparagine, GDP-mannose, and trehalose and the catabolic process of raffinose were activated. DEGs encoding antioxidants (spermidine) and antioxidase (CAT1, GPX4, DHAR2, and APX1) were much more up-regulated in embryos of KN27-3. The content of auxin (IAA), cis-zeatin riboside (cZR), and trans-zeatin riboside (tZR) in KN27-3 are higher than that in XLZ38 at five stages (from 12 h to 54 h). GA3 was expressed at a higher level in KN27-3 from 18 h to 54 h post imbibition compared to that in XLZ38. And abscisic acid (ABA) content of KN27-3 is lower than that in XLZ38 at five stages. Results from hormone content measurements and the related gene expression analysis indicated that IAA, CTK, and GA3 may promote germination of the cold-tolerant variety, while ABA inhibits it. These results expand the understanding of cottonseed germination and physiological regulations under chilling conditions by multiple pathways.