BXD Recombinant Inbred Mice as a Model to Study Neurotoxicity

BXD recombinant inbred (RI) lines represent a genetic reference population derived from a cross between C57BL/6J mice (B6) and DBA/2J mice (D2), which through meiotic recombination events possesses recombinant chromosomes containing B6 or D2 haplotype segments. The quantitative trait loci (QTLs) are the locations of segregating genetic polymorphisms and are fundamental to understanding genetic diversity in human disease susceptibility and severity. QTL mapping represents the typical approach for identifying naturally occurring polymorphisms that influence complex phenotypes. In this process, genotypic values at markers of known genomic locations are associated with phenotypic values measured in a segregating population. Indeed, BXD RI strains provide a powerful tool to study neurotoxicity induced by different substances. In this review, we describe the use of BXD RI lines to understand the underlying mechanisms of neurotoxicity in response to ethanol and cocaine, as well as metals and pesticide exposures.

Identifying New Resistance to Cassava Mosaic Disease and Validating Markers for the CMD2 Locus

Cassava (Manihot esculenta Crantz) is a crucial staple crop, and provides carbohydrate energy to more than half a billion people in the tropics. Cassava mosaic disease (CMD) is the most important disease of cassava in Africa. Since Sri Lanka Cassava Mosaic Virus (SLCMV) was first reported in South East Asia in 2015, establishing sustainable solutions to CMD has become a top priority for the cassava program at the International Center for Tropical Agriculture (CIAT) and its partners. In the present study, we screened two populations for CMD resistance: VNM142, 142 clones collected from farms throughout Vietnam, and CIAT102, 102 clones resistant to CMD or mites, which were introduced from CIAT. High broad-sense heritability was observed in all the trials (>0.80). From the population VNM142, eight clones showed high CMD resistance with CMD severity scores less than 2.0. Two resistant clones had the same DNA fingerprinting with the accessions CR63 (PER262 or TAI9) and KM57 (VNM8) in the genebank, respectively. To our knowledge, this is the first report of CMD resistance in the genebank at CIAT. We also used the two populations to validate the CMD markers S12_7926132 and S14_4626854. Both markers explained 51% of the population variance in the segregating population CIAT102, but only 11% in the diverse population VNM142. Thus, we concluded that the two CMD markers could not be used to select for CMD resistance in diverse populations, but could predict the CMD resistance in segregating populations when the susceptible parents do not have resistant marker alleles and the resistance of the CMD2 donors is confirmed.

A SmelAAT Acyltransferase Variant Causes a Major Difference in Eggplant (Solanum melongena L.) Peel Anthocyanin Composition

Eggplant berries are rich in anthocyanins like delphinidin-3-rutinoside (D3R) and nasunin (NAS), which are accumulated at high amounts in the peel. NAS is derived by D3R through acylation and glycosylation steps. The presence of D3R or NAS is usually associated with black-purple or lilac fruit coloration of the most cultivated varieties, respectively. Building on QTL mapping position, a candidate gene approach was used to investigate the involvement of a BAHD anthocyanin acyltransferase (SmelAAT) in determining anthocyanin type. The cDNA sequence comparison revealed the presence of a single-base deletion in D3R-type line ‘305E40’ (305E40_aat) with respect to the NAS-type reference line ‘67/3’. This is predicted to cause a frame shift mutation, leading to a loss of SmelAAT function and, thus, D3R retention. RT-qPCR analyses confirmed SmelAAT and 305E40_aat expression during berry maturation. In D3R-type lines, ‘305E40’ and ‘DR2’ overexpressing the functional SmelAAT allele from ‘67/3’, the transcript levels of the transgene, correlated with the accumulation of NAS in fruit peel. Furthermore, it was also found a higher expression of the transcript for glucosyltransferase Smel5GT1, putatively involved with SmelAAT in the last steps of anthocyanin decoration. Finally, an indel marker matching with anthocyanin type in the ‘305E40’ × ’67/3’ segregating population was developed and validated in a wide number of accessions, proving its usefulness for breeding purposes.

Assessment of Genetic Diversity of 62 F4 Population of Rapeseed (Brassica Napus L.) Through Multivariate Analysis

Rapeseed (Brassica napus L.) is the best one in respect of oil production. It is the order of the day to take better steps for production and quality improvement of our local cultivars. Broadening of genetic diversity in spring oilseed Brassica napus L. (AACC, 2n = 38), canola is important for continued improvement of this crop. Sixty-two genotypes in F4 generation of Brassica napus L. were evaluated to assess genetic diversity based on randomized complete block design with three replications at the experimental field of Sher-e-Bangla Agricultural University, Dhaka. Different Multivariate analyses were performed to classify 62 genotypes. On the basis of cluster analysis, all the genotypes were classified in five clusters. The cluster IV comprised the maximum number (19) of genotypes followed by same in cluster II (18). The cluster I and V comprised 10 and 9 genotypes respectively. The lowest number of genotypes was present in cluster II. The highest inter-cluster distance (10.309) was observed between the cluster I and IV and the genotypes of these clusters involved in hybridization may produce a wide spectrum of segregating population. The lowest inter-cluster distance (3.513) was observed between the cluster III and IV. The inter-cluster distances were larger than the intra-cluster distances. Considering cluster distance, inter genotypic distance and other agronomic performance G3, G4, G24, G35 and G51 might be suggested for future breeding program. SAARC J. Agric., 19(1): 15-25 (2021)

An Insertion Mutation Located on Putative Enhancer Regions of the MYB26-Like Gene Induce Inhibition of Anther Dehiscence Resulting in Novel Genic Male Sterility in Radish (Raphanus Sativus L.)

A novel male-sterility trait was identified in a radish (Raphanus sativus L.) population. Although the size of male-sterile anthers was comparable to that of normal flowers, no pollen grain was observed during anther dehiscence. However, dissection of male-sterile anthers revealed an abundance of normal pollen grains. Analysis of segregating populations showed that a single recessive locus, designated RsMs1 conferred male sterility. Based on two radish draft genome sequences, molecular markers were developed to delimit the genomic region harboring the RsMs1. The region was narrowed down to approximately 27 kb after analyzing recombinants selected from 7,511 individuals of a segregating population. Sequencing of the delimited region yielded six putative genes including four genes expressed in the floral tissue, and one gene with significant differential expression between male-fertile and male-sterile individuals of a segregating population. This differentially expressed gene was orthologous to the Arabidopsis MYB26 gene, which played a critical role in anther dehiscence. Excluding a synonymous single nucleotide polymorphism in exon3, no polymorphism involving coding and putative promoter regions was detected between alleles. A 955-bp insertion was identified 7.5 kb upstream of the recessive allele. Highly conserved motifs among four Brassicaceae species were identified around this insertion site, suggesting the presence of putative enhancer sequences. A functional marker was developed for genotyping of the RsMs1 based on the 955-bp insertion. A total of 120 PI accessions were analyzed using this marker, and 11 accessions were shown to carry the recessive RsMs1 allele.

Evaluation of Groundnut Segregating Population for Resistance to Sclerotium rolfsii. using an Efficient Field Screening Technique

Background: Stem rot of groundnut caused by Sclerotium rolfsii Sacc. is one of the major constraint to groundnut production in many countries and yield losses upto 10-25% were recorded. Screening of groundnut genotypes for resistance to stem rot under field conditions is complicated by the non-uniform spatial distribution of the pathogen.Methods: A total of 165 segregants derived from TAG 24 and R 9227 were evaluated for resistance to stem and pod rot during rainy and summer seasons by using sick plot technique. The field is artificially inoculated at 30 days interval.Result: Among different parameters, maximum phenotypic variability and heritability were observed for disease at 30, 60, 90 days after sowing. The strong negative associations were observed for disease incidence and plant population and positive association were observed for test weight and pod weight per plant. The higher number of superior segregants was observed for pod weight per plant followed by oil content and test weight as compared to both the parents. Generally, high frequencies of desirable segregants were observed for oil content combined with pod weight per plant followed by test weight and pod weight per plant. Out of 165 lines, only six lines showed moderate resistance to Sclerotium rolfsii with good yield attributing characters, further these lines can be utilized in future breeding programme.

Mechanism of Leaf Vein Coloration and Inheritance of Leaf Vein Color, Flower Form, and Floral Symmetry in Gloxinia

Double-flowered gloxinia (Sinningia speciosa) cultivars with foliar variegation might have a greater market appeal as flowering foliage plants. Crosses were made among 16 gloxinia cultivars and their progenies were analyzed to determine the inheritance of leaf vein color, flower form, and floral symmetry. All plants from self-pollinating white-veined cultivars or crosses between white-veined and green-veined cultivars produced white veins. Progeny derived from self-pollinating plants of white-veined cultivars × green-veined cultivars segregated into a ratio of 3 white-veined:1 green-veined. All plants from self-pollinating or cross-pollinating single-flowered cultivars produced single flowers. Progeny of self-pollination or crosses between double-flowered cultivars segregated into a ratio of 3 double flowers:1 single flower. Contingency chi-square tests revealed that leaf vein color and flower form were inherited independently. New gloxinia progenies with homozygous white veins and double flowers were successfully developed from the F2 segregating population. Plants from self-pollinating or cross-pollinating cultivars with actinomorphic flowers produced actinomorphic flowers. A single dominant gene expressed in the homozygous or heterozygous state resulted in the zygomorphic flowers. Independent inheritance was observed between vein color and floral symmetry. Air spaces between the epidermis and the mesophyll cells were observed in the white, but not in the green, leaf vein portions. Net photosynthesis did not differ significantly between the white vein and adjacent green portion of the same leaf.