Contribution of the different omega-3 fatty acid desaturase genes to the cold response in soybean

Fatty acid profiles from the plasma membrane and detergent resistant membranes of two plant species

It is essential to establish the composition of the plant plasma membrane in order to understand its organization and behavior under continually changing environments. Knowledge of the lipid phase, in particular the fatty acid (FA) complex repertoire, is important since FAs determine many of the physical-chemical membrane properties. FAs are constituents of the membrane glycerolipid and sphingolipid backbones and can also be linked to some sterols. In addition, FAs are components of complex lipids that can constitute membrane micro-domains, and the use of detergent-resistant membranes is a common approach to study their composition. The diversity and cellular allocation of the membrane lipids containing FAs are very diverse and the approaches to analyze them provide only general information. In this work, a detailed FA analysis was performed using highly purified plasma membranes from bean leaves and germinating maize embryos and their respective detergent-resistant membrane preparations. The analyses showed the presence of a significant amount of very long chain FAs (containing 28C, 30C and 32C), in both plasma membrane preparations from bean and maize, that have not been previously reported. Herein is demonstrated that a significant enrichment of very long chain saturated FAs and saturated FAs can occur in detergent-resistant membrane preparations, as compared to the plasma membranes from both plant species. Considering that a thorough analysis of FAs is rarely performed in purified plasma membranes and detergent-resistant membranes, this work provides qualitative and quantitative evidence on the contributions of the length and saturation of FAs to the organization of the plant plasma membrane and detergent-resistant membranes.

Transcriptome sequencing and identification of cold tolerance genes in hardy Corylus species (C. heterophylla Fisch) floral buds

Background

The genus Corylus is an important woody species in Northeast China. Its products, hazelnuts, constitute one of the most important raw materials for the pastry and chocolate industry. However, limited genetic research has focused on Corylus because of the lack of genomic resources. The advent of high-throughput sequencing technologies provides a turning point for Corylus research. In the present study, we performed de novo transcriptome sequencing for the first time to produce a comprehensive database for the Corylus heterophylla Fisch floral buds.

Results

The C. heterophylla Fisch floral buds transcriptome was sequenced using the Illumina paired-end sequencing technology. We produced 28,930,890 raw reads and assembled them into 82,684 contigs. A total of 40,941 unigenes were identified, among which 30,549 were annotated in the NCBI Non-redundant (Nr) protein database and 18,581 were annotated in the Swiss-Prot database. Of these annotated unigenes, 25,311 and 10,514 unigenes were assigned to gene ontology (GO) categories and clusters of orthologous groups (COG), respectively. We could map 17,207 unigenes onto 128 pathways using the Kyoto Encyclopedia of Genes and Genomes Pathway (KEGG) database. Additionally, based on the transcriptome, we constructed a candidate cold tolerance gene set of C. heterophylla Fisch floral buds. The expression patterns of selected genes during four stages of cold acclimation suggested that these genes might be involved in different cold responsive stages in C. heterophylla Fisch floral buds.

Conclusion

The transcriptome of C. heterophylla Fisch floral buds was deep sequenced, de novo assembled, and annotated, providing abundant data to better understand the C. heterophylla Fisch floral buds transcriptome. Candidate genes potentially involved in cold tolerance were identified, providing a material basis for future molecular mechanism analysis of C. heterophylla Fisch floral buds tolerant to cold stress.

Changes in RNA Splicing in Developing Soybean (Glycine max) Embryos

Developing soybean seeds accumulate oils, proteins, and carbohydrates that are used as oxidizable substrates providing metabolic precursors and energy during seed germination. The accumulation of these storage compounds in developing seeds is highly regulated at multiple levels, including at transcriptional and post-transcriptional regulation. RNA sequencing was used to provide comprehensive information about transcriptional and post-transcriptional events that take place in developing soybean embryos. Bioinformatics analyses lead to the identification of different classes of alternatively spliced isoforms and corresponding changes in their levels on a global scale during soybean embryo development. Alternative splicing was associated with transcripts involved in various metabolic and developmental processes, including central carbon and nitrogen metabolism, induction of maturation and dormancy, and splicing itself. Detailed examination of selected RNA isoforms revealed alterations in individual domains that could result in changes in subcellular localization of the resulting proteins, protein-protein and enzyme-substrate interactions, and regulation of protein activities. Different isoforms may play an important role in regulating developmental and metabolic processes occurring at different stages in developing oilseed embryos.

A temporal regulatory mechanism controls the different contribution of endoplasmic reticulum and plastidial ω-3 desaturases to trienoic fatty acid content during leaf development in soybean (Glycine max cv Volania)

We analyzed the molecular mechanism controlling ω-3 fatty acid desaturases during seed germination and leaf development in soybean. During germination, soybean seeds were characterized by a high 18:2(Δ9,12) level (more than 50%) and reduced 18:3(Δ9,12,15) content (10%). Interestingly, transcripts from all endoplasmic reticulum (GmFAD3A and GmFAD3B) and plastidial (GmFAD7-1/GmFAD7-2 or GmFAD8-1/GmFAD8-2) desaturase genes were detected during seed germination. Upon germination, soybean trifoliate leaf development was accompanied by an increase in linolenic acid (18:3(Δ9,12,15)). Our data showed that transcripts corresponding to the endoplasmic reticulum ω-3 desaturases GmFAD3A and GmFAD3B decreased with leaf development. No changes in the expression profile of the plastidial ω-3 desaturases GmFAD7-1 and GmFAD7-2 genes were detected. On the contrary, GmFAD8-2 transcript levels increased while GmFAD8-1 transcripts decreased during leaf development. Given this expression profile, our data suggested the existence of a temporal regulatory mechanism controlling ω-3 desaturases during leaf development in which the endoplasmic reticulum ω-3 desaturases would be more important in young leaves while plastidial ω-3 desaturases might contribute to 18:3(Δ9,12,15) production in mature leaves. Photosynthetic cell cultures showed 18:3(Δ9,12,15) levels similar to those from leaves. No changes in the 18:3(Δ9,12,15) content or expression of the ω-3 desaturase genes were detected along the cell culture cycle. A comparison of our data with those available in Arabidopsis or wheat suggested that the regulatory mechanism controlling the expression and activity of both endoplasmic reticulum and plastidial desaturases during leaf development might differ among plant species.

Identification and functional analysis of a Δ6-desaturase gene and the effects of temperature and wounding stresses on its expression in Microula sikkimensis leaves

A Δ6-desaturase gene was isolated from Microula sikkimensis. Sequence analysis indicated that the gene, designated MsD6DES, had an open reading frame of 1,357 bp and encoded 448 amino acids. Heterologous expression in tobacco indicated that MsD6DES can use endogenous substrates to synthesize γ-linolenic acid (GLA, 18:3(Δ 6,9,12)) and octadecatetraenoic acid (OTA, 18:4(Δ 6,9,12,15)). MsD6DES transcripts were distributed in all tested tissues, with high expression levels in seeds and young leaves. The effects of temperature and wounding stresses on MsD6DES expression were analyzed. The results indicated that temperature regulates MsD6DES at the transcriptional level. MsD6DES expression increased first, reaching a maximum 4 h after low-temperature treatment. A slight increase in MsD6DES transcript levels was also observed under high temperature. We found that the response of MsD6DES to temperature stress was different from those of fungi and algae. In addition, MsD6DES was found to be wound-inducible.