Project description:In somatic embryogenesis, embryos are formed from a single or small group of somatic cells in response to stress and hormonal stimuli. In this study, a high-throughput phosphoproteomic analysis was used to identify and quantify phosphoproteins related to the acquisition of embryogenic competence in sugarcane. Embryogenic (EC) and nonembryogenic (NEC) calli were compared at the multiplication phase, resulting in the identification of 1279 phosphoproteins. After the differential accumulation analysis, 163 phosphoproteins were identified as unique to EC, and nine were unique to NEC, while 51 were upaccumulated, and 40 were downaccumulated in EC compared to NEC. These phosphopeptides were mainly single phosphorylated peptides, with serine residues representing the major site of phosphorylation. The motif-x analysis revealed the enrichment of [xxxpSPxxx], [RxxpSxxx] and [xxxpSDxxx] motifs, which are predicted phosphorylation sites for several kinases related to stress responses. Gene ontology enrichment revealed an overrepresentation of biological processes involved in embryonic development, showing that EC-related phosphoproteins (unique to EC and upaccumulated) were associated with stress responses, regulation of gene expression and epigenetic modifications. The NEC-related phosphoproteins (unique to NEC and downaccumulated) were associated with the translation process. In this sense, EC-related phosphoproteins described as potential regulators of abiotic stress tolerance in response to ABA-induced signals such as OSK3 (a catalytic subunit of SnRK1), ABF1, LEAs, REM4.1 and RD29Bs were identified. On the other hand, the NEC-related phosphoproteins EDR1 and PP2Ac-2 were negative regulators of ABA, suggesting a role of ABA in the acquisition of embryogenic competence linked to stress tolerance. Moreover, EC-related phosphoproteins associated with epigenetic modifications, such as HDA6, HDA19, and TPL, as well as those involved in embryo development, including ASIL1, M3KE1, MCM2, and GRV2, were identified as putative potential regulators of embryogenic competence. Our results provide novel data that may help elucidate the phosphorylation mechanisms controlling the activity, affinity and localization of specific proteins during somatic embryogenesis and suggest a role for these proteins in the hormonal signalling cascade leading to stress adaptation by reprogramming genetic expression.

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.

Dataset Information

Somatic embryogenesis of Pinus nigra

Publications

Insights into the early stage of Pinus nigra Arn. somatic embryogenesis using discovery proteomics.

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