Developmental stimuli and stress factors affect expression of ClGLP1, an emerging allergen-related gene in Citrus limon

Genome-wide analysis of the GLP gene family and overexpression of GLP1-5-1 to promote lignin accumulation during early somatic embryo development in Dimocarpus longan

Longan (Dimocarpus longan Lour.) is an economically important subtropical fruit tree. Its fruit quality and yield are affected by embryo development. As a plant seed germination marker gene, the germin-like protein (GLP) gene plays an important role in embryo development. However, the mechanism underlying the role of the GLP gene in somatic embryos is still unclear. Therefore, we conducted genome-wide identification of the longan GLP (DlGLP) gene and preliminarily verified the function of DlGLP1-5-1. Thirty-five genes were identified as longan GLP genes and divided into 8 subfamilies. Based on transcriptome data and qRT‒PCR results, DlGLP genes exhibited the highest expression levels in the root, and the expression of most DlGLPs was upregulated during the early somatic embryogenesis (SE) in longan and responded to high temperature stress and 2,4-D treatment; eight DlGLP genes were upregulated under MeJA treatment, and four of them were downregulated under ABA treatment. Subcellular localization showed that DlGLP5-8-2 and DlGLP1-5-1 were located in the cytoplasm and extracellular stroma/chloroplast, respectively. Overexpression of DIGLP1-5-1 in the globular embryos (GEs) of longan promoted the accumulation of lignin and decreased the H₂O₂ content by regulating the activities of ROS-related enzymes. The results provide a reference for the functional analysis of DlGLPs and related research on improving lignin accumulation in the agricultural industry through genetic engineering.

OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity

Copper (Cu) and cadmium (Cd) are common heavy metal pollutants. When Cd and excessive Cu accumulate in plants, plant growth is reduced. Our previous study showed that Germin-like proteins (GLPs), which exist in tandem on chromosomes, are a class of soluble glycoproteins that respond to Cu stress. In this study, hydroponic cultures were carried out to investigate the effect of GLP on Cd and Cu tolerance and accumulation in rice. The results showed that knockout of a single OsGLP8-2 gene or ten OsGLP genes (OsGLP8-2 to OsGLP8-11) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the glp8-2 and glp8-(2-11) mutants displayed a more sensitive phenotype based on the plant height, root length, and dry biomass of the rice seedlings. Correspondingly, Cu and Cd concentrations in the glp8-2 and glp8-(2-11) mutants were significantly higher than those in the wild-type (WT) and OsGLP8-2-overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-OsGLP8-2 line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, glp8-2, and glp8-(2-11). The expression of lignin synthesis genes in the OsGLP8-2-overexpressing line was significantly higher than that in the WT, glp8-2, and glp8-(2-11). The SOD activity of OsGLP8-2, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that OsGLP8-2 is involved in heavy metal-induced antioxidant defense in rice. Our findings clearly suggest that OsGLPs participate in responses to heavy metal stress by lignin deposition and antioxidant defense capacity in rice, and OsGLP8-2 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.

Identification and functional analysis of a pollen fertility-associated gene GhGLP4 of Gossypium hirsutum L

KEY MESSAGE

Cotton male fertility-associated gene GhGLP4, encoding a germin-like protein, is essential for anthers development by keeping ROS homeostasis through reducing H2O2 level. Utilization of heterosis is an important way to increase cotton yield and improve fiber quality in hybrid cotton development programs. Male sterility is used in the development of cotton hybrids to reduce the cost of hybrid seed production by eliminating the process of emasculation. From the transcriptome analysis of genic male sterile mutant (ms1) and its background C312 of G. hirsutum, a gene encoding germin-like protein (GhGLP4) was found significantly down-regulated in different developmental stages of ms1 anthers. To explore the gene function in cotton fertility, GhGLP4 was further studied and interfered by virus-induced gene silencing. In the GhGLP4 interfered cotton lines, the expression level of GhGLP4 was significantly decreased in the stamens, and the down-regulation of GhGLP4 resulted in pollen sac closure, stigma exertion, filament shortening, decrease in the number of anthers and complete male sterility. The expression levels of respiratory burst oxidase homologs (Rboh, NADPH oxidase) were significantly altered. Further investigation showed that the SOD activity decreased while the H2O2 content increased in the atypical stamens. These results indicated that GhGLP4 gene affected the cotton anther development through maintenance of ROS homeostasis by H2O2 reduction.

Enhanced thermo-tolerance in transgenic potato (Solanum tuberosum L.) overexpressing hydrogen peroxide-producing germin-like protein (GLP)

Germins and germin-like proteins (GLPs) were reported to participate in plant response to biotic and abiotic stresses involving hydrogen peroxide (H₂O₂) production, but their role in mitigating heat stress is poorly understood. Here, we investigated the ability of a Solanum tuberosum L. GLP (StGLP) gene isolated from the yeast cDNA library generated from heat-stressed potato plants and characterized its role in generating innate and/or acquired thermo-tolerance to potato via genetic transformation. The transgenic plants exhibited enhanced tolerance to gradual heat stress (GHS) compared with sudden heat shock (SHS) in terms of maximal cell viability, minimal ion leakage and reduced chlorophyll breakdown. Further, three StGLP transgenic lines (G9, G12 and G15) exhibited enhanced production of H₂O₂, which was either reduced or blocked by inhibitors of H₂O₂ under normal and heat stress conditions. This tolerance was mediated by up-regulation of antioxidant enzymes (catalase, ascorbate peroxidase and glutathione reductase) and other heat stress-responsive genes (StHSP70, StHSP20 and StHSP90) in transgenic potato plants. These results demonstrate that H₂O₂ produced by over-expression of StGLP in transgenic potato plants triggered the reactive oxygen species (ROS) scavenging signaling pathways controlling antioxidant and heat stress-responsive genes in these plants imparting tolerance to heat stress.

In vitro antileishmanial potentialities of essential oils from Citrus limon and Pistacia lentiscus harvested in Tunisia

Leishmaniasis is a tropical parasitic disease that affects up to 12 million people worldwide. Current chemotherapies have limitations such as toxicity, high cost, and parasite resistance. This work aims to select an essential oil (EssOil) isolated from the Tunisian flora as a new antileishmanial candidate. Two plants were chosen for their antileishmanial potential: Citrus limon (Citrus) and Pistacia lentiscus (Pistacia). Each of these plants was harvested from two different sites (area 1 and area 2). Extracted EssOils were characterized using GC-MS. Their antiparasitic activity against axenic and intracellular Leishmania major amastigotes and their cytotoxicity were assessed. Citrus EssOil from area 1 displayed an interesting activity against L. major intramacrophage amastigotes with IC₅₀ value at 4.2 ± 1.3 μg/mL. Interestingly, this activity was close to that of miltefosine. Moderate activities against intracellular amastigote were observed for Pistacia EssOil from area 1 and Citrus EssOil from area 2. However, low cytotoxicity with high selectivity index was proved only for Citrus EssOil from area 1, revealing its safety for macrophages. This study also demonstrated for the first time the antileishmanial activity of EssOil extracted from Citrus limon leaves. The EssOil interesting activity could be related to the lipophilic properties of terpenes that were shown in literature to contribute to the disruption of parasite intracellular metabolic pathways.

Fruit volatilome profiling through GC × GC-ToF-MS and gene expression analyses reveal differences amongst peach cultivars in their response to cold storage

Peaches have a short shelf life and require chilling during storage and transport. Peach aroma is important for consumer preference and determined by underlying metabolic pathways and gene expression. Differences in aroma (profiles of volatile organic compounds, VOCs) have been widely reported across cultivars and in response to cold storage. However, few studies used intact peaches, or used equilibrium sampling methods subject to saturation. We analysed VOC profiles using TD-GC × GC-ToF-MS and expression of 12 key VOC pathway genes of intact fruit from six cultivars (three peaches, three nectarines) before and after storage at 1 °C for 7 days including 36 h shelf life storage at 20 °C. Two dimensional GC (GC × GC) significantly enhances discrimination of thermal desorption gas chromatography time-of-flight mass spectrometry (TD-GC-ToF-MS) and detected a total of 115 VOCs. A subset of 15 VOCs from analysis with Random Forest discriminated between cultivars. Another 16 VOCs correlated strongly with expression profiles of eleven key genes in the lipoxygenase pathway, and both expression profiles and VOCs discriminated amongst cultivars, peach versus nectarines and between treatments. The cultivar-specific response to cold storage underlines the need to understand more fully the genetic basis for VOC changes across cultivars.

Isolation and structure elucidation of constituents of Citrus limon, Isodon japonicus, and Lansium domesticum as the cancer prevention agents

In the course of our research to investigate the cancer prevention potency of natural products derived from plant materials, we isolated fifty-five compounds, including twenty-one new compounds from the peels of Citrus limon, aerial parts of Isodon japonicus, and leaves of Lansium domesticum. The chemical structures of the isolated compounds were elucidated by chemical/physicochemical evidence, and nuclear magnetic resonance spectroscopy and mass spectrometry results. Moreover, the absolute stereochemistry of the new compounds were elucidated by various techniques such as chemical synthesis, modified Mosher’s method, Cu-Kα X-ray crystallographic analysis, and comparison of experimental and predicted electronic circular dichroism data. The antimutagenic effects of the isolated and structure-elucidated compounds against heterocyclic amines, 3-amino-1,4-dimethyl-5H-pyrido [4,3-b]indole (Trp-P-1) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), were evaluated by the Ames test and in vivo micronucleus test. In this review, we present the comprehensive results of the antimutagenic effects of the isolated natural products.

The allelochemical farnesene affects Arabidopsis thaliana root meristem altering auxin distribution

Farnesene is a sesquiterpene with semiochemical activity involved in interspecies communication. This molecule, known for its phytotoxic potential and its effects on root morphology and anatomy, caused anisotropic growth, bold roots and a "left-handedness" phenotype. These clues suggested an alteration of auxin distribution, and for this reason, the aim of the present study was to evaluate its effects on: i) PIN-FORMED proteins (PIN) distribution, involved in polar auxin transport; ii) PIN genes expression iii) apical meristem anatomy of primary root, in 7 days old Arabidopsis thaliana seedlings treated with farnesene 250 μM. The following GFP constructs: pSCR::SCR-GFP, pDR5::GFP,pPIN1::PIN1-GFP, pPIN2::PIN2-GFP, pPIN3::PIN3-GFP, pPIN4::PIN4-GFP and pPIN7::PIN7-GFP were used to evaluate auxin distribution. Farnesene caused a reduction in meristematic zone size, an advancement in transition zone, suggesting a premature exit of cells from the meristematic zone, a reduction in cell division and an impairment between epidermal and cortex cells. The auxin-responsive reporter pDR5::GFP highlighted that auxin distribution was impaired in farnesene-treated roots, where auxin distribution appeared maximum in the quiescent center and columella initial cells, without extending to mature columella cells. This finding was further confirmed by the analysis on PIN transport proteins distribution, assessed on individual constructs, which showed an extreme alteration mainly dependent on the PIN 3, 4 and 7, involved in pattern specification during root development and auxin redistribution. Finally, farnesene treatment caused a down-regulation of all the auxin transport genes studied. We propose that farnesene affected auxin transport and distribution causing the alteration of root meristem, and consequently the left-handedness phenotype.

In Arabidopsis thaliana Cadmium Impact on the Growth of Primary Root by Altering SCR Expression and Auxin-Cytokinin Cross-Talk

Cadmium is one of the most widespread pollutant in both terrestrial and marine environment, and its inhibitory effect on plant growth has been largely demonstrated. However, the molecular mechanisms underlying Cd toxicity in plant and mainly in root, as the first organ sensing soil heavy metals, need to be better investigated. To this aim, in the present work we analyzed the growth and the organization of Arabidopsis thaliana primary root in seedlings exposed to Cd (25 and 50 μM) for 8 days starting from germination. Root length, root meristem size, and organization were evaluated together with the behavior of some of the major molecular players in root growth and patterning. In particular, by using different GFP transgenic lines, we monitored: (i) the expression pattern of WOX5 and SCR transcription factors involved in the establishment and maintenance of stem cell niche and in the control of meristem size; (ii) the expression pattern of the IAA-inducible pDR5::GFP reporter, PIN 1, 2, 3, 7 auxin carriers and TCSn::GFP cytokinin-sensitive sensor as relevant components of hormone circuit controlling root growth. We report that Cd exposure inhibits primary root growth via affecting RAM stem cell niche and root radial pattern. At the molecular level, an impairment of auxin maximum accumulation at the root tip, related to a down-regulation and mislocalisation of PIN proteins, and an enhancement of TCSn::GFP cytokinin-sensitive sensor signal is also detected under Cd treatment, thus suggesting an alteration in the homeostasis of auxin/cytokinin signaling. Moreover, and for the first time Cd toxicity on root growth and pattern has been related to a misexpression of SCR transcription factors which is known to interplay with auxin/cytokinin cross-talk in the control of RAM maintenance and activity.

A dehydrin gene isolated from feral olive enhances drought tolerance in Arabidopsis transgenic plants

Dehydrins belong to a protein family whose expression may be induced or enhanced by developmental process and environmental stresses that lead to cell dehydration. A dehydrin gene named OesDHN was isolated and characterized from oleaster (Olea europaea L. subsp. europaea, var. sylvestris), the wild form of olive. To elucidate the contribution of OesDHN in the development of drought tolerance, its expression levels were investigated in oleaster plants during development and under drought stress condition. The involvement of OesDHN in plant stress response was also evaluated in Arabidopsis transgenic lines, engineered to overexpress this gene, and exposed to a controlled mild osmotic stress. OesDHN expression was found to be modulated during development and induced under mild drought stress in oleaster plants. In addition, the Arabidopsis transgenic plants showed a better tolerance to osmotic stress than wild-type plants. The results demonstrated that OesDHN expression is induced by drought stress and is able to confer osmotic stress tolerance. We suggest a role for OesDHN, as a putative functional marker of plant stress tolerance.