Molecular cloning of class III chitinase gene from Avicennia marina and its expression analysis in response to cadmium and lead stress

Cloning and Expression of Class I Chitinase Genes from Four Mangrove Species under Heavy Metal Stress

Chitinases are believed to act as defense proteins when plants are exposed to heavy metal stress. Typical Class I chitinase genes were cloned from Bruguiera gymnorrhiza, Rhizophora stylosa, Kandelia obovata, and Avicennia marina using the methods of reverse-transcription-polymerase chain reaction and rapid amplification of cDNA ends. All four cDNA sequences of chitinase from the mangrove plants were 1092 bp in length and consisted of an open reading frame of 831 bp, encoding 276 amino acids. However, there were differences in the sequences among the four mangrove species. Four gene proteins have a signal peptide, are located in the vacuole, and belong to the GH19 chitinase family. The sequence of chitinase was highly similar to the protein sequences of Camellia fraternal chitinases. A real-time polymerase chain reaction was used to analyze the chitinase expressions of the above four mangrove species exposed to different concentrations of heavy metal at different times. The gene expression of chitinase was higher in Bruguiera gymnorrhiza leaves than in other mangrove plant species. With an increase in heavy metal stress, the expression level of Bruguiera gymnorrhiza increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Molecular Cloning and Expression Analysis of the Typical Class III Chitinase Genes from Three Mangrove Species under Heavy Metal Stress

Chitinases are considered to act as defense proteins when plants are exposed to heavy metal stresses. Typical class III chitinase genes were cloned from Kandelia obovate, Bruguiera gymnorrhiza, and Rhizophora stylosa by using RT-PCR and RACE and named KoCHI III, BgCHI III, and RsCHI III. Bioinformatics analysis revealed that the three genes encoding proteins were all typical class III chitinases with the characteristic catalytic structure belonging to the family GH18 and located outside the cell. In addition, there are heavy metal binding sites in the three-dimensional spatial structure of the type III chitinase gene. Phylogenetic tree analysis indicated that CHI had the closest relationship with chitinase in Rhizophora apiculata. In mangrove plants, the balance of the oxidative system in the body is disrupted under heavy metal stress, resulting in increased H2O2 content. Real-time PCR illustrated that the expression level under heavy metal stress was significantly higher than that in the control group. Expression levels of CHI III were higher in K. obovate than in B. gymnorrhiza and R. stylosa. With the increase in heavy metal stress time, the expression level increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Characterization and Expression Analysis of Four Cadmium-Tolerance-Associated Genes of Avicennia marina (Forsk.)

Mangroves colonize the intertidal area of estuaries (e.g., Pichavaram, Payardia, and Mai Po) with remarkable cadmium (Cd) pollution. A study on the mechanism of mangrove plant response to Cd pollution can help to understand the adaptive characteristics of plants under Cd stress. This study explored the roles of peroxidase (PRX), pectate lyase (PL), and phytosulfokine (PSK) genes in cadmium tolerance of mangrove Avicennia marina. Full-length sequences of four genes (i.e., AmPRX1, AmPRX2, AmPL, and AmPSK) associated with metal tolerance were identified with suppression subtractive hybridization and rapid amplification of cDNA ends. These genes showed the characteristic features of the respective protein family, indicating functions similar to other plant proteins. Real-time quantitative PCR analysis demonstrated that cadmium exposure resulted in differences in expression patterns among the tissues. Our findings emphasize the complex regulatory mechanism of these four genes in response to trace metal pollution and reveal their functions in metabolic signaling during the stress response.

New Evidence of Semi-Mangrove Plant Barringtonia racemosa in Soil Clean-Up: Tolerance and Absorption of Lead and Cadmium

Mangrove plants play an important role in the remediation of heavy-metal-contaminated estuarine and coastal areas; Barringtonia racemosa is a typical semi-mangrove plant. However, the effect of heavy metal stress on this plant has not been explored. In this study, tolerance characteristics and the accumulation profile of cadmium (Cd) and lead (Pb) in B. racemosa were evaluated. The results indicated that B. racemosa exhibited a high tolerance in single Cd/Pb and Cd + Pb stress, with a significant increase in biomass yield in all treatment groups, a significant increase in plant height, leaf area, chlorophyll and carotenoid content in most treatment groups and without significant reduction of SOD, POD, MDA, proline content, Chl a, Chl b, Chl a + b, Car, ratio of Chl a:b and ratio of Car:Chl (a + b). Cd and Pb mainly accumulated in the root (≥93.43%) and the content of Cd and Pb in B. racemosa was root > stem > leaf. Pb showed antagonistic effects on the Cd accumulation in the roots and Cd showed antagonistic or synergistic effects on the Pb accumulation in the roots, which depended on the concentration of Cd and Pb. There was a significant synergistic effect of Cd and Pb enrichment under a low Cd and Pb concentration treatment. Thus, phytoremediation could potentially use B. racemosa for Cd and Pb.

Genetic and molecular mechanisms underlying mangrove adaptations to intertidal environments

Mangroves are halophytic plants belonging to diverse angiosperm families that are adapted to highly stressful intertidal zones between land and sea. They are special, unique, and one of the most productive ecosystems that play enormous ecological roles and provide a large number of benefits to the coastal communities. To thrive under highly stressful conditions, mangroves have innovated several key morphological, anatomical, and physio-biochemical adaptations. The evolution of the unique adaptive modifications might have resulted from a host of genetic and molecular changes and to date we know little about the nature of these genetic and molecular changes. Although slow, new information has accumulated over the last few decades on the genetic and molecular regulation of the mangrove adaptations, a comprehensive review on it is not yet available. This review provides up-to-date consolidated information on the genetic, epigenetic, and molecular regulation of mangrove adaptive traits.

Genome-wide identification and expression analysis of the Brassica oleracea L. chitin-binding genes and response to pathogens infections

Chitinase family genes were involved in the response of Brassica oleracea to Fusarium wilt, powdery mildew, black spot and downy mildew. Abstract Chitinase, a category of pathogenesis-related proteins, is believed to play an important role in defending against external stress in plants. However, a comprehensive analysis of the chitin-binding gene family has not been reported to date in cabbage (Brassica oleracea L.), especially regarding the roles that chitinases play in response to various diseases. In this study, a total of 20 chitinase genes were identified using a genome-wide search method. Phylogenetic analysis was employed to classify these genes into two groups. The genes were distributed unevenly across six chromosomes in cabbage, and all of them contained few introns (≤ 2). The results of collinear analysis showed that the cabbage genome contained 1-5 copies of each chitinase gene (excluding Bol035470) identified in Arabidopsis. The heatmap of the chitinase gene family showed that these genes were expressed in various tissues and organs. Two genes (Bol023322 and Bol041024) were relatively highly expressed in all of the investigated tissues under normal conditions, exhibiting the expression characteristics of housekeeping genes. In addition, under four different stresses, namely, Fusarium wilt, powdery mildew, black spot and downy mildew, we detected 9, 5, 8 and 8 genes with different expression levels in different treatments, respectively. Our results may help to elucidate the roles played by chitinases in the responses of host plants to various diseases.

Proline metabolism and molecular cloning of AmP5CS in the mangrove Avicennia marina under heat stress

Proline is one of the most important compatible osmolyte in cells, which accumulates in response to various stresses, including salt, water deficit, heavy metal, pathogen infection and extreme temperature. In this study, a growth chamber was employed to simulate heat environment for Avicennia marina seedlings. We detected some physiological indices in the leaves of A. marina at 40 °C, including the activity of delta-1-pyrroline-5-carboxylate synthase (P5CS), the content of free proline and soluble protein, transpiration rate and membrane permeability, and discussed the relationship between these five indices and heat resistant ability. And then a P5CS gene was cloned from A. marina using homologous cloning and rapid amplification of cDNA ends methods. It was designated as AmP5CS, encoding a protein that contained a feedback inhibition site of proline, proA, proB, conserved Leu zipper, GSA-DH domain and other functional domains of P5CS protein in high plants. Expression analysis of AmP5CS gene indicated it was involved in heat stress response. It is the first time that P5CS from A. marina has been cloned and the findings laid the foundation of figuring out heat resistant mechanisms and relieving heat damage, which is significant during global warming.

Molecular cloning and expression of AmCDPK from mangrove Avicennia marina under elevated temperature

Considered as an essential calcium sensor, the calcium-dependent protein kinase (CDPK) family plays a critical part in terrestrial plants' responses to both biotic and abiotic stresses. In the study, Avicennia marina was proved to have better heat tolerance than other species. A CDPK gene was cloned from mangrove species A. marina using RACE-PCR and designated as AmCDPK. By predicting and analyzing its properties, structures and expression patterns, we found that the amino acid sequence, containing a kinase domain and four EF-hand Ca²⁺-binding sites, shared high identity with Handroanthus impetiginosus and Sesamum indicum. Quantitative real-time PCR data analysis suggested that AmCDPK demonstrated significant up-regulation under heat stress. It is likely that AmCDPK is a versatile gene involved in various stresses, including dehydration, cold, light, defense and ABA stress responses by analyzing cis-elements. It is the first time that CDPKs from mangroves have been cloned and our results brought evidence to the effect of AmCDPK on heat stress, which is particularly important under the background of global warming.

Expression and biochemical characterization of a novel chitinase ChiT-7 from the metagenome in the soil of a mangrove tidal flat in China

Chitinases play an important role in the process of chitin bioavailability. In this study, we cloned a new chitinase gene and characterized its recombinant protein. The new 1251 bp gene of chitinase (ChiT-7) was cloned from the metagenome of the mangrove tidal flat soil in the city of Zhangzhou in Fujian Province (China) by genome walking. The gene encoded a mature protein with 381 amino acids, which manifested certain sequence similarity (59% identity) to characterized GH18 chitinases. The mature protein of ChiT-7 was successfully expressed in E. coli BL21 (DE3). After purification, the specific activity of the recombinant enzyme was 0.63 U/mg at the optimal pH of 6.0 and the optimal temperature of 45 °C. The rChiT-7 was active over a wide pH range, and the residual enzyme activity reached 80% or higher at 30 °C-50 °C. rChiT-7 hydrolyzed colloidal chitin with (GlcNAc)2 and GlcNAc as the main final products. Structural analysis of ChiT-7 indicated that ChiT-7 could be a processive chitinase. rChiT-7 manifested characteristics analogous to those of fungi and actinomycetes and exhibited sequence homology.

Morphological Responses and Gene Expression of Grain Amaranth (Amaranthus spp.) Growing under Cd

Phytoremediation efficiency depends on the ability of plants to accumulate, translocate and resist high levels of metals without symptoms of toxicity. This study was conducted to evaluate the potential of grain amaranth for remediation of soils contaminated with Cd. Three grain amaranth varieties, “Pribina” (A. cruentus), “Zobor” (A. hypochondriacus x A. hybridus) and Plainsman (A. hypochondriacus x A. hybridus) were tested under different level of Cd (0, 5, 10 and 15 mg/L) in a hydroponic experimental treatment. All could be classified as Cd excluders or Cd-hypertolerant varieties able to grow and accumulate significant amounts of Cd from the hydroponic solution, preferentially in the roots. Under the highest level of Cd exposure, qRT-PCR expression analysis of five stress-related genes was examined in above- and below-ground biomass. The results show that the Cd concentration significantly increased the mRNA level of chitinase 5 (Chit 5) in amaranth roots as the primary site of metal stress. The involvement of phytochelatin synthase (PCS1) in Cd detoxification is suggested. Based on our findings, we can conclude that variety “Pribina” is the most Cd-tolerant among three tested and can be expected to be used in the phytomanagement of Cd loaded soils as an effective phytostabiliser.

Changes in exoskeleton surface roughness and expression of chitinase genes in mud crab Macrophthalmus japonicus following heavy metal differences of estuary

Risk assessment of heavy metals is important for the health evaluation of inhabiting species in aquatic ecosystem. This study investigated whether chitin exoskeleton of mud crab Macrophthalmus japonicus is affected by heavy metals in estuary sediments in Korea. We compared heavy metal concentrations and analyzed the expression of M. japonicus chitinase genes, which play the crucial role in the formation of chitin exoskeleton. Concentrations of heavy metals were highly observed in crab body inhabiting Hampyeong among estuarine sites. High expressions of chitinase 1 were observed in crab gill and hepatopancreas from Myodo, which is the site with the lowest concentration of heavy metal in crab body. The surface roughness of the exoskeleton decreased with the increased concentration of heavy metals accumulated in the crab body. These results suggest that the total bioconcentration of heavy metals in crabs affected the expression of chitinase genes and changes in the exoskeleton surface roughness.