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Digital gene expression analysis of ACMV-infected cassava

ABSTRACT: Cassava mosaic disease caused by cassava begomoviruses is the most serious disease of cassava in Africa. However, the molecular mechanisms leading to symptom development of infected cassava plants are poorly understood. Here a high throughput digital gene expression profiling (DGE) based on Illumina Solexa sequencing technology was used to investigate the global transcriptional response of cassava to the African cassava mosaic virus infection. Results showed that 3,210 genes were differentially expressed in virus-infected cassava leaves. Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that photosynthesis related genes were most affected, which was consistent with the chlorotic symptom on the infected leaves. The upregulation of chlorophyll degradation genes, e.g. the genes encoding chlorophyllase and pheophorbide a oxygenase, as well as the downregulation of the major apoproteins genes in light harvesting complex II (LHCII) identified by the DGE analysis were confirmed by qRT-PCR. Together with the reduction of chlorophyll b content and fewer grana stacks in the infected leaf cells, this study reveals that the degradation of chlorophyll plays an important role during ACMV symptom development for the first time. Meanwhile, we believe that the non-lethal effect on photosystem is a trick for virus to avoid fierce host immune response and a result of the long-term co-evolution. This study will provide a road map for future investigations into virus symptom development.

ORGANISM(S): Manihot esculenta

PROVIDER: GSE47224 | GEO | 2014/04/01

SECONDARY ACCESSION(S): PRJNA205160

REPOSITORIES: GEO

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Project description:Here we performed a transcriptomic study on complete symptom development process of CMV-infected Nicotiana tabacum using Solexa/Illumina's high-throughput digital gene expression (DGE) system. 12 DGE libraries (from six virus-infected samples and six corresponding mock-inoculated samples) were constructed, and the gene expression variations between the virus-infected sample and the mock-inoculated sample in each symptom stage were compared. Thousands of differentially expressed genes were obtained by the comparison, and KEGG pathway analysis of these genes suggested that many biological processes (such as phtosynthesis, pigment metabolism and plant-pathogen interaction) were related to the symptom development. The authenticity of the DGE data was further confirmed by analyzing real-time RT-PCR using several random-selected genes. We sequenced a cDNA library constructed from mixture of total RNA from six virus-infected samples and six mock-inoculated samples to get gene information for tobacco leaves in different symptom stages, including vein clearing, mosaic, severe chlorosis, partial recovery, total recovery and re-mosaic, and 95,916 Unigenes were obtained Tobacco leaves were inoculated by CMV-infected leaf homogenate and healthy leaf homogenate, respectivley. Six time points with different symptom stage were selected, and one virus-infect sample and one mock-inoculated sample were collected at each time. In order to average out variation of different plants, five leaves from five different plants were mixed to prepare every RNA sample. Twelve individual tag libraries of samples (six infected samples and six mock-inoculated samples) were constructed in parallel. For the gene expression analysis, the twelve samples were grouped into six groups, and each group contained a virus-infected sample and a mock-inoculated sample collected at the same time. In each group, the DGE data of virus-infected sample were compared to that of mock-inoculated sample to obtain the gene expression variations. Illumina sequencing of transcripts from virus-infected and mock-inoculated samples to get gene information for tobacco leaves in different symptom stages. In order to get more gene information, the systemically infected leaves and mock-inoculated leaves were harvested at six time points and five leaves from five different plants were collected at each time point. The RNA-Seq analysis provided gene information for mock-inoculated and virus-infected tobacco leaves in different symptom stages.

Project description:External application of acetic acid has been recently reported to enhance the survival to drought in plants such as Arabidopsis, rapeseed, maize, rice and wheat, but the effects of acetic acid application on increased drought tolerance in woody plants such as a tropical crop “cassava” remain elusive. A molecular understanding of acetic acid-induced drought avoidance in cassava will contribute to the development of technology that can be used to enhance drought tolerance without resorting to transgenic technology or advancements in cassava cultivation. In the present study, morphological, physiological and molecular responses to drought were analyzed in cassava after the treatment with acetic acid. Results indicated that the acetic acid-treated cassava plants had a higher level of drought avoidance than water-treated, control plants. Specifically, higher leaf relative water content, and chlorophyll and carotenoid levels were observed as soils dried out during the drought treatment. Leaf temperatures in acetic acid-treated cassava plants were higher relative to leaves on plants pretreated with water and the increase of ABA content was observed in leaves of acetic acid-treated plants, suggesting that stomatal conductance and the transpiration rate in leaves of acetic acid-treated plants decreased to maintain relative water contents and avoid drought. Transcriptome analysis revealed that the acetic acid treatment increased the expression of ABA signaling-related genes, such as OPEN STOMATA 1　(OST1) and protein phosphatase 2C; as well as drought response and tolerance-related genes, such as outer membrane tryptophan-rich sensory protein (TSPO), and heat shock proteins. Collectively, the external application of acetic acid enhances drought avoidance in cassava through the upregulation of ABA signaling pathway genes and several stress response- and tolerance-related genes. These data support the idea that adjustments of the acetic acid application to plants is useful to enhance drought tolerance in order to minimize the growth inhibition in the agricultural field.

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Digital gene expression analysis of ACMV-infected cassava

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