Project description:White clover mosaic virus (WCMV) is a major pathogen of white clover (Trifolium repens L.), with significant effects on yield and persistence. Due to the absence of natural sources of WCMV resistance a transgenic strategy has been employed to produce plants constitutively expressing WCMV replicase gene derivatives, designed to inhibit the propagation of WCMV through an RNA silencing mechanism. A 12,000 feature oligonucleotide microarray has been used to identify global changes in host plant, in addition to virus genome-encoded gene expression associated with WCMV infection in non-transgenic and transgenic WCMV-resistant white clover. Pairwise comparison between the transcriptome of mock-inoculated non-transgenic and WCMV-inoculated transgenic plants provides clear evidence for substantial equivalence between these two genotype/treatments, and demonstrate the efficacy of the transgenic strategy. WCMV- inoculated non-transgenic plants exhibit elevated abundance of many virus-encoded, and host immune response-specific transcripts compared to the transgenic resistant plants or mock-inoculated non-transgenic plants. By contrast, relative to inoculated sensitive plants, the majority of significantly up-regulated genes in mock-inoculated non-transgenic plants or WCMV-inoculated transgenic plants are markers of healthy cellular function. These results, and the occurrence of levels of WCMV-encoded transcripts in inoculated transgenic plants equivalent to those in virus-free plants, confirm the validity of the transgenic RNA silencing approach.<br>
Project description:Red clover (Trifolium pratense L.) is one of the most important legume forage species in temperate livestock agriculture. Tetraploid red clover cultivars are generally producing less seed than diploid cultivars. Improving the seed setting potential of tetraploid cultivars is necessary in order to utilize the high forage quality and environmentally sustainable nitrogen fixation of red clover. Two genotypes, one from cv.Tripo with weak seed setting and one from cv.Lasang with strong seed setting, were selected based on data from field experiments for transcriptome analysis of developing flower buds. De novo and reference based analyses of transcriptome assemblies were conducted to study the global transcriptome changes from early to late developmental stages of flower development of the two contrasting red clover genotypes. Transcript profiles, gene ontology enrichment and KEGG pathway analysis indicate that genes related to flower development, pollen pistil interactions, photosynthesis and embryo development are differentially expressed between the Tripo and Lasang genotypes. A significant number of genes related to pollination was overrepresented in Lasang, which might be a reason for its good seed setting ability. The candidate genes detected in this study might be used to develop molecular tools for breeding tetraploid red clover varieties with improved seed yield potentials.
Project description:Legume plants form symbiotic relationships with diazotrophic bacteria called rhizobia. During such symbiosis, plants provide bacteria with preferred carbon sources such as malate and succinate in return for essential reduced nitrogen. Compatible interactions result in a series of plant root modifications that eventually result in nodule formation. Bacteria living in the nodule cells fix nitrogen via the nitrogenase enzyme complex. Interestingly, as in plant-pathogen interactions, incompatibility in legume-rhizobia associations is also regulated in a genotype-specific manner. For example, the dominant Rj2 gene is presumed to help exclude poor nitrogen-fixing or less-beneficial rhizobia such as B. japonicum USDA122 (U122). The process likely involves recognition of bacterial effectors by host receptor proteins similar to the perception of pathogenic microbes. Our results show that genetic exclusion of incompatible rhizobia in the root requires conserved molecular components of the plant immune response pathway and results in the induction of systemic signaling in the distal tissue. To better understand the mechanism underlying incompatible rhizobia-induced systemic signaling, we compared the transcriptional changes in the foliar tissue of Rj2 plants inoculated with compatible or incompatible rhizobia strains, using RNA-Seq analysis.