Biology subjects

Sheat, S.

Publications and source records attributed to Sheat, S..

3 recordsLinked to original sources

bioRxiv2025

Identification of immune response genes of cassava during early phases of cassava brown streak virus infection

Cassava brown streak disease (CBSD) caused by the ipomoviruses CBSV and UCBSV, poses a significant threat to cassava crops and the destruction of tuberous roots leads to substantial yield losses. Virus resistance identified in some South American cassava germplasm lines inhibits virus replication and movement and, is a complete immunity of some lines or, a restriction of the virus replication to phloem companion cells and root infection in others. To further explore the resistance responses and identify potential resistance genes, a time-course RNA-Seq study was conducted comparing gene expression of a virus-susceptible cassava TMS 96/0304 with a cassava line restricting CBSV to the roots and a cassava DSC 167 (COL2182), immune to the virus. Differential gene expression patterns across leaves, stems, and roots revealed substantial differences between susceptible and resistant genotypes. Temporal analysis highlighted significant variations in the number of differentially expressed genes (DEGs), particularly in stem tissues at one day after inoculation (DAI), with notable overexpression observed in the resistant lines DSC 167 (436 DEGs) and DSC 260 (335 DEGs). In contrast, significant expression changes were noted only at 10 DAI in the virus infected TMS 96/0304 (737 DEGs). Several DEGs in resistant genotypes were associated with proteins involved in hormonal regulation, defense and immunity, transcriptional regulation, stress response, cell structure, and signal transduction. The analysis indicates that virus resistance in the studied lines is driven by early-stage regulation of genes for which specific functions remain to be elucidated.

plant biology↗

bioRxiv2025

Rhizoctonia theobromae associated with a severe witches' broom outbreak in cassava of the Brazilian rainforest and evidence of its Southeast Asian origin

Cassava witches broom disease (CWBD) has emerged as a significant threat to cassava production in the Oiapoque region of Amapa, Brazil. Diseased plants exhibit stunted growth, vascular necrosis, abnormal shoot proliferation, and distinctive broom-like appearance. This study aimed to characterize the disease and identify its causal agent(s). The assessment by high-throughput sequencing of total nucleic acids (DNA and RNA) from affected cassava tissues revealed Rhizoctonia theobromae (syn. Ceratobasidium theobromae) associated with CWBD. PCR-based detection using species-specific primers confirmed the presence of R. theobromae in 74% of symptomatic samples. Genetic diversity analysis based on the Ca2+/calmodulin-dependent protein kinase gene showed low variability among Brazilian isolates compared with Asian populations, suggesting their recent introduction. This first report of R. theobromae causing CWBD in Brazil follows a recent report of the disease from French Guiana and highlights the urgent need for effective measures to prevent the further spread of this emerging pathogen, which poses a deadly threat to cassava cultivation in the rainforest, a significant risk to cassava production in Brazil, and regions with similar eco-climatic conditions.

pathology↗

bioRxiv2024

The haplotype-resolved assembly of COL40 a cassava (Manihot esculenta) line with broad-spectrum resistance against viruses causing Cassava brown streak disease unveils a region of highly repeated elements on chromosome 12

Cassava (Manihot esculenta Grantz) is a vital staple crop for millions of people, particularly in Sub-Saharan Africa, where it is a primary source of food and income. However, cassava production is threatened by several viral diseases, including cassava brown streak disease, which causes severe damage to the edible storage roots. Current cassava varieties in Africa lack effective resistance to this disease, leading to significant crop losses. We investigated the genetic diversity of cassava and identifed new sources of resistance to the viruses causing cassava brown streak disease. The cassava line, COL40, from a South American germplasm collection showed broad-spectrum resistance against all known strains of the viruses that cause this disease. To further understand the genetic basis of this resistance, we sequenced the genome of COL40 and produced a high-quality, haplotype-resolved genome assembly. This genomic resource provides new insights into cassavas genetic architecture, particularly in regions associated with disease resistance. The sequence reveals significant structural variation, including transposable elements, inversions, and deletions, which may contribute to the resistance phenotype. The reference genome assembly presented here will provide a valuable genomic resource for studying the cassava brown streak resistance and will help in accelerating breeding efforts to introduce virus resistance into African cassava varieties. By identifying genetic variants linked to resistance, future breeding programs can develop cassava cultivars that are more resilient to viral threats, enhancing food security and livelihoods for smallholder farmers across regions affected by the disease.

genomics↗