Assessment of Castor Plant (Ricinus communis L.) Tolerance to Heavy Metal Stress-A Review

Increased urbanization and industrialization have greatly contributed to the emission of higher amount of heavy metals such as cadmium,nickel,and lead into the environment.These metals are non-biodegradable and toxic,causing much effects on plants and by extension to animals and humans,which have become a major global concern.The inherent ability of plants to resist heavy metal toxicity seems to be the most sustainable and cost-effective strategy.Castor plant is widely studied due to its tolerance to the effects of heavy metal contaminated soils,owing to its large biomass content and high accumulating capacity.Castor plants to some extent can tolerate elevated levels of heavy metals through several developed mechanisms,such as activation of antioxidant enzymes,exclusion,accumulation of proline,compartmentalization,organic acid exudation,and phytochelatins.Molecular studies have identified some stress-responsive to aid the tolerance of heavy metals in castor.Stress caused by heavy metal toxicity affects seedling growth,biomass,photosynthetic pigments,protein level,and nutrient uptake of castor plant.The response of castor,however,to these stresses differs among cultivars,metal type and concentration,and time of metal applied.This review aims to summarize the physiological responses and various defense mechanisms of castor to tolerate and eradicate heavy metal toxicity and some stress-responsive genes identified at transcriptional and posttranscriptional levels that confer metal tolerance in this plant.

Growth Enhancement of Dunaliella salina by Microbubble Induced Airlift Loop Bioreactor (ALB)—The Relation between Mass Transfer and Growth Rate

The efficiency of a novel microalgal culture system (an airlift loop bioreactor [ALB] engaged with a fluidic oscillator to produce microbubbles) is compared with both a conventional ALB (producing fine bubbles without the fluidic oscillator) and non-aerated flask culture. The impact of CO2 mass transfer on Dunaliella salina growth is assessed, through varying the gas (5% CO2, 95% N2) dosing flow rate. The results showed that approximately 6 - 8 times higher chlorophyll content was achieved in the aerated ALB cultures than in the non-aerated flasks, and there was a 20% - 40% increase in specific growth rate of D. salina in the novel ALB with microbubbles when compared with the conventional ALB cultures. The increase in chlorophyll content was found to be proportional to the total amount of CO2 mass transfer. For the same dosing time and flow rate, higher CO2 mass transfer rate (microbubble dosing) resulted in a greater growth rate.

Construction ofcastorfunctionalmarkers fingerprint andanalysis of geneticdiversity

In order to provide a molecular basis for selecting good hybrid combinations for the identification of castor bean germplasm resources,fingerprint and genetic diversity analysis of 52 castor bean materials from 12 regions in 5 countries were constructed by using the Functinal Markers(FMs)associated with fatty acid metabolism-related genes.A total of 72 alleles were amplified by 29 pairs of FMs with an average of 2.483 per marker and the polymorphic information content was 0.103–0.695.Shannon’s information index(I),observed heterozygosity(Ho)and expected heterozygosity(He)were 0.699,0.188 and 0.436 respectively.The clustering results indicated that the castor germplasm could be divided into two groups with the genetic similarity coefficient of 0.59.The genetic similarity of 12 regions ranged from 0.518 to 0.917 and the genetic distance was between 0.087 and 0.658.A total of 5 pairs of core primers were screened to construct a digital fingerprint of different castor germplasm resources,which could distinguish all 52 germplasms.This study provides a scientific basis for screening high-quality castor germplasm resources and broadening the genetic basis of castor breeding at the molecular level.

Residues and sources of HCHs and DDTs in the sediments of land-based sewage outlet to the Zhanjiang Bay, China

Due to the large usage of DDT-containing antifouling paints and lindane in China, heavy residuals of DDTs and HCHs have been found in many fishing harbors, but there is lack of studies on this issue for the Zhanjiang Bay which is an important fishing harbor and mariculture zone in South China. To evaluate the pollution status and sources of HCHs and DDTs in the Zhanjiang Bay, the concentrations, spatial distributions and sources in the sediments of 11 land-based sewage outlets to the Zhanjiang Bay were investigated. Since the 1980 s, HCHs residuals had obviously decreased in studied areas, but DDTs had little change, even abnormally high levels were found in some sites. The content percentages and diagnostic ratios of HCHs isomers and DDTs showed that the source of HCHs was derived from soils around the bay and recent input of lindane, and DDTs were from historical residues of technical DDTs and fresh input of DDT-containing antifouling paints on fishing ships. Based on sediment quality guidelines, DDTs would be of more concern for the ecotoxicological risk on marine environment and adverse effects on benthonic organisms. This study indicated that lindane and DDT-containing products may be still used in some places of Zhanjiang City. It should be urgent to control their usage and clean the DDTs-contaminated sites by the local government.

Rapid Identification of a Candidate Gene Related to Fiber Strength Using a Superior Chromosome Segment Substitution Line from Gossypium hirsutum × Gossypium barbadense via Bulked Segregant RNA-Sequencing

Cotton is the most widely cultivated commercial crop producing natural fiber around the world.As a critical trait for fiber quality,fiber strength principally determined during the secondary wall thickening period.Based on the developed BC5F3:5 CSSLs(chromosome segment substitution lines)from Gossypium hirsutum CCRI36×G.barbadense Hai 1,the superior MBI9915 was chosen to construct the secondary segregated population BC7F2 with its recurrent parent CCRI36,which was subsequently subjected to Bulk segregant RNA-sequencing(BSR-seq)for rapid identification of candidate genes related to fiber strength.A total of 4 fiber-transcriptome libraries were separately constructed and sequenced,including two parents(CCRI36 and MBI9915)and two extreme pools at 20 DPA(days post anathesis).Through multiple comparisons,536 DEGs(differentially expressed genes)were overlapped at 20 DPA.Allelic-polymorphism comparison in mRNA sequences revealed 831 highly probable SNPs between two extreme pools related to fiber strength.Linkage analysis was performed between two extreme pools with SNP-index method.Eighteen correlated regions with 1981 annotation genes were obtained between two pools at 20 DPA,of which 12 common DEGs were similarly identified both between two parents and two pools.One gene(Gh_A07G0837)in the candidate region related to fiber strength was differentially expressed in both parents and extreme pools and involved in fiber strength development through reactive oxygen species(ROS)activity.Co-expression analysis of Gh_A07G0837 showed that Gh_A07G0837 may cooperate with other genes to regulate fiber strength.The reliability of BSR-seq results was validated by the quantitative real-time PCR(qRT-PCR)experiments on 5 common DGEs 20 DPA.Co-expressed analysis results indicated that there were some genes expressed especially low in MBI9915,resulting in good fiber strength.Focusing on bulked segregant analysis on the extreme pools derived from superior CSSL population,this study indicates that BSR-seq can be efficiently applied on rapid identification of candidate genes related to fiber strength,which make contributions to our understanding of fiber quality formation in cotton.

Genome-wide identification,characterization,and expression analysis of aluminum-activated malate transporter genes(ALMTs)in Gossypium hirsutum L.

Aluminum-activated malate transporters(ALMT)are widely involved in plant growth and metabolic processes,including adaptation to acid soils,guard cell regulation,anion homeostasis,and seed development.Although ALMT genes have been identified in Arabidopsis,wheat,barley,and Lotus japonicus,little is known about its presence in Gossypium hirsutum L.In this study,ALMT gene recognition in diploid and tetraploid cotton were done using bioinformatics analysis that examined correlation between homology and evolution.Differentially regulated ALMT genetic profile in G.hirsutum was examined,using RNA sequencing and qRT-PCR,during six fiber developmental time-points,namely 5 d,7 d,10 d,15 d,20 d,and 25 d.We detected 36 ALMT genes in G.hirsutum,which were subsequently annotated and divided into seven sub-categories.Among these ALMT genes,34 had uneven distribution across 14/26 chromosomes.Conserved domains and gene structure analysis indicated that ALMT genes were highly conserved and composed of exons and introns.The GhALMT gene expression profile at different DPA(days post anthesis)in different varieties of G.hirsutum is indicative of a crucial role of ALMT genes in fiber development in G.hirsutum.This study provides basis for advancements in the cloning and functional enhancements of ALMT genes in enhancing fiber development and augmenting high quality crop production.

Comprehensive analysis of NAC transcription factors in diploid Gossypium: sequence conservation and expression analysis uncover their roles during fiber development

Determining how function evolves following gene duplication is necessary for understanding gene expansion.Transcription factors(TFs)are a class of proteins that regulate gene expression by binding to specific cis-acting elements in the promoters of target genes,subsequently activating or repressing their transcription.In the present study,we systematically examined the functional diversification of the NAC transcription factor(NAC-TFs)family by analyzing their chromosomal location,structure,phylogeny,and expression pattern in Gossypium raimondii(Gr)and G.arboreum(Ga).The 145 and 141 NAC genes identified in the Gr and Ga genomes,respectively,were annotated and divided into 18 subfamilies,which showed distinct divergence in gene structure and expression patterns during fiber development.In addition,when the functional parameters were examined,clear divergence was observed within tandem clusters,which suggested that subfunctionalization had occurred among duplicate genes.The expression patterns of homologous gene pairs also changed,suggestive of the diversification of gene function during the evolution of diploid cotton.These findings provide insights into the mechanisms underlying the functional differentiation of duplicated NAC-TFs genes in two diploid cotton species.

Constructing a high-density linkage map for Gossypium hirsutum × Gossypium barbadense and identifying QTLs for lint percentage

To introgress the good fiber quality and yield from Gossypium barbadense into a commercial Upland cotton variety, a high‐density simple sequence repeat （SSR） genetic linkage map was developed from a BC1F1 population of Gossypium hirsutum × Gossypium barbadense. The map com-prised 2,292 loci and covered 5115.16 centiMorgan （cM） of the cotton AD genome, with an average marker interval of 2.23 cM. Of the marker order for 1,577 common loci on this new map, 90.36% agrees well with the marker order on the D genome sequence genetic map. Compared with five pub-lished high‐density SSR genetic maps, 53.14% of marker loci were newly discovered in this map. Twenty‐six quantitative trait loci （QTLs） for lint percentage （LP） were identified on nine chromosomes. Nine stable or common QTLs could be used for marker‐assisted selection. Fifty percent of the QTLs were from G. barbadense and increased LP by 1.07%–2.41%. These results indicated that the map could be used for screening chromosome substitution segments from G. barbadense in the Upland cotton background, identifying QTLs or genes from G. barbadense, and further developing the gene pyramiding effect for improving fiber yield and quality.