Project description:Somatic embryogenesis (SE), a morphogenic process that takes advantage of the regenerative potential of plants to replicate whole plants starting from somatic explants, can be a source of variation with potential applications in plant breeding. It is one of the most suitable tools to apply functional genomics studies and genetic improvement in plants. However, beyond a few pioneering works mainly focused on model plants, the molecular characterization of SE mechanisms is still elusive, especially for woody species. In grapevine, this process is affected by many factors such as explant type, culture conditions and, most importantly, genotype. Many cultivars, in fact, have shown recalcitrance to tissue culture and transformation, and very low SE competence. Thus, the understanding of SE competence behind the regenerative aptitude is fundamental to the widespread application of the so-called “next-generation breeding techniques”, such as cisgenesis and genome editing, in grapevine. Here, we explored genetic and epigenetic features of the SE process in grapevine by investigating the behavior of two genotypes showing opposite SE competence. Embryogenic tissues were induced from immature stamens excised from field-collected flower clusters of Sangiovese (highly competent for embryogenesis) and Cabernet Sauvignon (poorly competent for embryogenesis). A multilayered approach was used to profile mRNA, smallRNAs and methylated DNA with high-throughput sequencing technologies in the initial explants, on undifferentiated calli induced after 40 days of culture, and in embryogenic and non-embryogenic calli after 3 months of culture. A comprehensive comparison of transcriptomes of the different types of calli with the grapevine gene expression atlas revealed that, in grapevine, the dedifferentiation to the callus formation during the embryogenesis process occurs via a ‘berry’ developmental pathway. This is dissimilar from that shown in Arabidopsis, in which dedifferentiated calli are more similar to the tip of a root meristem. Interestingly, a Gene Ontology (GO) analysis revealed that secondary metabolism and gene expression regulation/epigenetics are the enriched functional categories of genes differentially down- and up-regulated in embryogenic vs non-embryogenic calli, respectively. These results prompted us to define the epigenetic landscape dynamics during SE in grapevine, revealing a significant increase in DNA methylation, especially in intergenic regions, in the embryogenic calli tissues. Finally, we proposed potential key regulators of SE in different genotypes that could represent putative targets of next-generation breeding techniques in grapevine.

Project description:Grapevine rupestris stem pitting-associated virus (GRSPaV) is a widespread virus affecting Vitis spp. Although it has established a compatible viral interaction in Vitis vinifera L. without the development of phenotypic alterations, it can occur as distinct variants that show different symptoms in diverse Vitis species. We investigated the changes induced by GRSPaV in V. vinifera cv Bosco, an Italian white grape variety, by combining agronomic, physiological, and molecular approaches, in order to provide comprehensive information about the global effects of GRSPaV. In two consecutive years, this virus caused a moderate decrease in physiological efficiency, yield performance, and sugar content in berries associated with several transcriptomic alterations. Transcript profiles were analysed by microarray techniques in petiole, leaf, and berry samples collected at véraison and by quantitative real-time RT-PCR (qRT-PCR) in a time course carried out at five relevant grapevine developmental stages. Global gene expression analyses showed that transcriptomic changes were highly variable among the different organs and the different phenological phases. GRSPaV triggers some unique responses in the grapevine at véraison, never reported before for other plant-virus interactions, such as an increase in transcripts involved in photosynthesis and CO2 fixation, associated with a moderate reduction in the photosynthesis rate and some defence mechanisms, and to an overlap with responses to water and salinity stresses. We hypothesise that the long co-existence between grapevine and GRSPaV has resulted in the evolution of a form of mutual adaptation between the virus and its host. This study contributes to elucidating alternative mechanisms used by infected plants to contend with viruses. The study was carried out in a vineyard planted in 2002 in Albenga (Liguria), North-West Italy, where a row was established with the white grape cultivar Bosco (V. vinifera L.). Microarray analysis was carried out on leaves, petioles, and berries collected at véraison (E-L35) in 2010. For each of the six GRSPaV-free and six GRSPaV-infected vines selected for the physiological and agronomical parameters evaluation, we collected 6 leaves (3 basal and 3 apical) with the related petioles and 12 berries from 3 different bunches. Samples from each organ were arbitrary pooled in 3 independent biological replicates and total RNA was extracted according to the method described by Gambino et al. (2008).

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HTS based monitoring of the efficiency of somatic embryogenesis and meristem culture as a method used for virus elimination in grapevine

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