Laser microdissection of paraffin-embedded plant tissues for transcript profiling

Rolling circle amplification of begomoviral DNA from a single nucleus isolated by laser dissection microscopy

Laser dissection microscopy (LDM) is a method for isolating organelles, a specific cell or cells/tissue of interest from microscopic regions with the help of a laser. Here we describe a LDM-based isolation of begomovirus infected Nicotiana benthamiana epidermal cells and nuclei, in combination with a fast method to prepare non-fixed leaf epidermal samples for LDM. The bipartite Abutilon mosaic virus (AbMV) was used in which the coat protein gene of DNA A was deleted and replaced by the open reading frame (ORF) coding for the green fluorescent protein (GFP, accession: U87624), agro-infiltrated together with DNA B, to visualize infected cells. GFP expressing epidermal cells or nuclei were isolated by LDM with the MMi Cellcut system and viral circular DNA was amplified by rolling circle amplification (RCA). Subsequently, the RCA product was incubated with the restriction enzymes BamHI and PstI and restriction fragments were separated on an agarose gel to prove presence of the viral genome. It was shown that even a single-isolated nucleus harbored enough material to produce a sufficient restriction fragment pattern to identify a begomovirus infected cell/nucleus.

Laser Capture Micro-Dissection Coupled to RNA Sequencing: A Powerful Approach Applied to the Model Legume Medicago truncatula in Interaction with Sinorhizobium meliloti

Understanding the development of multicellular organisms requires the identification of regulators, notably transcription factors, and specific transcript populations associated with tissue differentiation. Laser capture microdissection (LCM) is one of the techniques that enable the analysis of distinct tissues or cells within an organ. Coupling this technique with RNA sequencing (RNAseq) makes it extremely powerful to obtain a genome-wide and dynamic view of gene expression. Moreover, RNA sequencing allows two or potentially more interacting organisms to be analyzed simultaneously. In this chapter, a LCM-RNAseq protocol optimized for root and symbiotic root nodule analysis is presented, using the model legume Medicago truncatula (in interaction with Sinorhizobium meliloti in the nodule samples). This includes the description of procedures for plant material fixation, embedding, and micro-dissection; it is followed by a presentation of techniques for RNA extraction and amplification, adapted for the simultaneous analysis of plant and bacterial cells in interaction or, more generally, polyadenylated and non-polyadenylated RNAs. Finally, step-by-step statistical analyses of RNAseq data are described. Those are critical for quality assessment of the whole procedure and for the identification of differentially expressed genes.

Sample preparation for single cell transcriptomics: essential oil glands in Citrus fruit peel as an example

Many plant natural products are synthesized in specialized cells and tissues. To learn more about metabolism in these cells, they have to be studied in isolation. Here, we describe a protocol for the isolation of epithelial cells that surround secretory cavities in Citrus fruit peel. Cells isolated using laser microdissection are suitable for RNA isolation and downstream transcriptome analyses.

Laser-assisted microdissection applied to floral tissues

Cellular context can be crucial when studying developmental processes as well as responses to environmental variation. Several different tools have been developed in recent years to isolate specific tissues or cell types. Laser-assisted microdissection (LAM) allows for the isolation of such specific tissue or single cell-types purely based on morphology and cytology. This has the advantage that (1) cell types that are rare can be isolated from heterogeneous tissue, (2) no marker line with cell type-specific expression needs to be established, and (3) the method can be applied to non-model species and species that are difficult to genetically transform. The rapid development of next-generation sequencing (NGS) approaches has greatly advanced the possibilities to perform molecular analyses in diverse organisms. However, there is a mismatch between currently available cell isolation tools and their applicability to non-model organisms. Therefore, LAM will become increasingly popular in the study of diverse agriculturally or ecologically relevant plant species. Here, we describe a protocol that has been successfully used for LAM to isolate either whole floral organs or even single cell types in plants, e.g., Arabidopsis thaliana, Boechera spp., or tomato.

Visual analysis of transcriptome data in the context of anatomical structures and biological networks

The complexity and temporal as well as spatial resolution of transcriptome datasets is constantly increasing due to extensive technological developments. Here we present methods for advanced visualization and intuitive exploration of transcriptomics data as necessary prerequisites in order to facilitate the gain of biological knowledge. Color-coding of structural images based on the expression level enables a fast visual data analysis in the background of the examined biological system. The network-based exploration of these visualizations allows for comparative analysis of genes with specific transcript patterns and supports the extraction of functional relationships even from large datasets. In order to illustrate the presented methods, the tool HIVE was applied for visualization and exploration of database-retrieved expression data for master regulators of Arabidopsis thaliana flower and seed development in the context of corresponding tissue-specific regulatory networks.

A novel procedure for the quantitative analysis of metabolites, storage products and transcripts of laser microdissected seed tissues of Brassica napus

BACKGROUND

The biology of the seed is complicated by the extensive non-homogeneity (spatial gradients) in gene expression, metabolic conversions and storage product accumulation. The detailed understanding of the mechanisms underlying seed growth and storage therefore requires the development of means to obtain tissue-specific analyses. This approach also represents an important priority in the context of seed biotechnology.

RESULTS

We provide a guideline and detailed procedures towards the quantitative analysis of laser micro-dissected (LM) tissues in oilseed rape (Brassica napus). This includes protocols for laser microdissection of the seed, and the subsequent extraction and quantitative analysis of lipids, starch and metabolites (sugars, sugar phosphates, nucleotides, amino acids, intermediates of glycolysis and citric acid cycle). We have also developed a protocol allowing the parallel analysis of the transcriptome using Brassica-specific microarrays. Some data are presented regarding the compartmentation of metabolites within the oilseed rape embryo.

CONCLUSION

The described methodology allows for the rapid, combined analysis of metabolic intermediates, major storage products and transcripts in a tissue-specific manner. The protocols are robust for oilseed rape, and should be readily adjustable for other crop species. The suite of methods applied to LM tissues represents an important step in the context of both the systems biology and the biotechnology of oilseeds.