Geminiviruses and Food Security: A Molecular Genetics Perspective for Sustainable Agriculture in Africa.

The African continent is vulnerable to food insecurity. Increased food costs, job losses, and climate change force Africans to chronic hunger. Biotechnology can be used to mitigate this by using techniques such as CRISPR/Cas9 systems, TALENs, and ZFNs.

The selection and validation of reference genes for quantitative real-time PCR studies in near-isogenic susceptible and resistant tomato lines, infected with the geminivirus tomato curly stunt virus.

Quantitative real-time PCR (qPCR) is a sensitive and commonly used technique for gene expression profiling and provides insight into biological systems. Successful qPCR requires the use of appropriate reference genes for the normalization of data. In the present study, we aimed to identify and assess the best-suited reference genes in near-isogenic resistant (R) and susceptible (S) tomato lines infected with begomovirus Tomato curly stunt virus (ToCSV).

Real-time PCR data for reference candidate gene selection in tomato infected with Tomato curly stunt virus.

Real-time PCR (qPCR) is a useful and robust method of quantifying gene expression, provided that suitable reference genes are used to normalize the data. To date, suitable reference genes have not been validated for tomato gene expression changes in response to Tomato curly stunt virus (ToCSV). RT-qPCR was conducted on resistent (R) and susceptible (S) tomato leave tissue infected with ToCSV at 35 days post infection.

Small RNA and methylation responses in susceptible and tolerant landraces of cassava infected with South African cassava mosaic virus.

Endogenous small RNAs (sRNAs) associated with gene regulatory mechanisms respond to virus infection, and virus-derived small RNAs (vsRNAs) have been implicated in recovery or symptom remission in some geminivirus-host interactions. Transcriptional gene silencing (TGS) (24 nt vsRNAs) and post transcriptional gene silencing (PTGS) (21-23 nt vsRNAs) have been associated with geminivirus intergenic (IR) and coding regions, respectively. In this Illumina deep sequencing study, we compared for the first time, the small RNA response to South African cassava mosaic virus (SACMV) of cassava landrace TME3 which shows a recovery and tolerant phenotype, and T200, a highly susceptible landrace.

Virus tolerance and recovery from viral induced-symptoms in plants are associated with transcriptome reprograming.

Plant recovery from viral infection is characterized by initial severe systemic symptoms which progressively decrease, leading to reduced symptoms or symptomless leaves at the apices. A key feature to plant recovery from invading nucleic acids such as viruses is the degree of the host's initial basal immunity response. We review current links between RNA silencing, recovery and tolerance, and present a model in which, in addition to regulation of resistance (R) and other defence-related genes by RNA silencing, viral infections incite perturbations of the host physiological state that trigger reprogramming of host responses to by-pass severe symptom development, leading to partial or complete recovery.

Transcriptional analysis of South African cassava mosaic virus-infected susceptible and tolerant landraces of cassava highlights differences in resistance, basal defense and cell wall associated genes during infection.

Background: Cassava mosaic disease is caused by several distinct geminivirus species, including South African cassava mosaic virus-[South Africa:99] (SACMV). To date, there is limited gene regulation information on viral stress responses in cassava, and global transcriptome profiling in SACMV-infected cassava represents an important step towards understanding natural host responses to plant geminiviruses.

Results: A RNA-seq time course (12, 32 and 67 dpi) study, monitoring gene expression in SACMV-challenged susceptible (T200) and tolerant (TME3) cassava landraces, was performed using the Applied Biosystems (ABI) SOLiD next-generation sequencing platform.