Overexpression of rice thaumatin-like protein (Ostlp) gene in transgenic cassava results in enhanced tolerance to Colletotrichum gloeosporioides f. sp. Manihotis
Cassava (Manihot esculenta Crantz) is the most important staple food for more than 300 million people in Africa, and anthracnose disease caused by Colletotrichum gloeosporioides f. sp. manihotis is the most destructive fungal disease affecting cassava production in sub-Saharan Africa. The main objective of this study was to improve anthracnose resistance in cassava through genetic engineering. Transgenic cassava plants harbouring rice thaumatin-like protein (Ostlp) gene, driven by the constitutive CaMV35S promoter, were generated using Agrobacterium-mediated transformation of friable embryogenic calli (FEC) of cultivar TMS 60444. Molecular analysis confirmed the presence, integration, copy number of the transgene all the independent transgenic events. Semi-quantitative RT-PCR confirmed high expression levels of Ostlp in six transgenic lines tested. The antifungal activity of the transgene against Colletotrichum gloeosporioides pathogen was evaluated using the leaves and stem cuttings bioassay. The results demonstrated significantly delayed disease development and reduced size of necrotic lesions in leaves and stem cuttings of all transgenic lines compared to the leaves and stem cuttingss of non-transgenic control plants. Therefore, constitutive overexpression of rice thaumatin-like protein in transgenic cassava confers enhanced tolerance to the fungal pathogen C. gloeosporioides f. sp. manihotis. These results can therefore serve as an initial step towards genetic engineering of farmer-preffered cassava cultivars for resistance to anthracnose disease.
Development of next-generation sequencing (NGS)-based SSRs in African nightshades: Tools for analyzing genetic diversity for conservation and breeding
African nightshade is an indigenous leafy vegetable in Eastern and Western Africa that is valued for its high nutrient content and potential to generate income. Efforts to improve this crop have been hampered by limited information available on intra- and interspecific genetic diversity. Here, we present data on the development and application of polymorphic simple sequence repeat (SSR) markers in a broad collection of entries (gene bank accessions, landraces from farmers, breeding lines and commercial cultivars) from two species of African nightshades, Solanum scabrum(Mill.) and S. villosum (Mill.). Next generation sequencing information was used to develop 16 polymorphic SSR markers that revealed genetic diversity within and between the 54 entries collected from various geographic locations in Sub-Saharan Africa. High levels of polymorphism were detected within entries, indicating gene flow between entries and/or a low intensity of selection during development of breeding lines and improved cultivars. As a consequence, they have retained sufficient variation for further selection within the improved germplasm. The two species were clearly distinct, and S. scabrum was found to be less diverse compared to S. villosum. Furthermore, some entries were identified as probably misclassified based on morphological markers as they can clearly be placed within the gene pool of either S. scabrum or S. villosum using the SSR data. In addition to the diversity studies, we determined the genome size and ploidy of a selection of 29 entries helpful for the design of future NGS-based marker projects. All entries of S. scabrum were found to be hexaploid, whereas entries of S. villosum were tetraploid with a haploid genome size of all samples slightly varying by approximately 1 pg. Finally, we also determined pollen viability parameters, which differed significantly between the two species but did not correlate to any of the other parameters measured.
Cross-species multiple environmental stress responses: An integrated approach to identify candidate genes for multiple stress tolerance in sorghum (Sorghum bicolor (L.) Moench) and related model species
Crop response to the changing climate and unpredictable effects of global warming with adverse conditions such as drought stress has brought concerns about food security to the fore; crop yield loss is a major cause of concern in this regard. Identification of genes with multiple responses across environmental stresses is the genetic foundation that leads to crop adaptation to environmental perturbations. This study introduces an integrated approach to assess candidate genes for multiple stress responses across species. The work identified target genes linked to Quantitative Trait Loci (QTLs) controlling yield and stress tolerance in sorghum and closely related species.