Lipid transfer proteins in coffee: isolation of Coffea orthologs, Coffea arabica homeologs, expression during coffee fruit development and promoter analysis in transgenic tobacco plants

The non-specific lipid transfer protein McLTPII.9 of Mentha canadensis is involved in peltate glandular trichome density and volatile compound metabolism

Mentha canadensis L. is an important spice crop and medicinal herb with high economic value. The plant is covered with peltate glandular trichomes, which are responsible for the biosynthesis and secretion of volatile oils. Plant non-specific lipid transfer proteins (nsLTPs) belong to a complex multigenic family involved in various plant physiological processes. Here, we cloned and identified a non-specific lipid transfer protein gene (McLTPII.9) from M. canadensis, which may positively regulate peltate glandular trichome density and monoterpene metabolism. McLTPII.9 was expressed in most M. canadensis tissues. The GUS signal driven by the McLTPII.9 promoter in transgenic Nicotiana tabacum was observed in stems, leaves, and roots; it was also expressed in trichomes. McLTPII.9 was associated with the plasma membrane. Overexpression of McLTPII.9 in peppermint (Mentha piperita. L) significantly increased the peltate glandular trichome density and total volatile compound content compared with wild-type peppermint; it also altered the volatile oil composition. In McLTPII.9-overexpressing (OE) peppermint, the expression levels of several monoterpenoid synthase genes and glandular trichome development-related transcription factors-such as limonene synthase (LS), limonene-3-hydroxylase (L3OH), geranyl diphosphate synthase (GPPS), HD-ZIP3, and MIXTA-exhibited varying degrees of alteration. McLTPII.9 overexpression resulted in both a change in expression of genes for terpenoid biosynthetic pathways which corresponded with an altered terpenoid profile in OE plants. In addition, peltate glandular trichome density was altered in the OE plants as well as the expression of genes for transcription factors that were shown to be involved in trichome development in plants.

Birch pollen-The unpleasant herald of spring

Type I respiratory allergies to birch pollen and pollen from related trees of the order Fagales are increasing in industrialized countries, especially in the temperate zone of the Northern hemisphere, but the reasons for this increase are still debated and seem to be multifaceted. While the most important allergenic molecules of birch pollen have been identified and characterized, the contribution of other pollen components, such as lipids, non-allergenic immunomodulatory proteins, or the pollen microbiome, to the development of allergic reactions are sparsely known. Furthermore, what also needs to be considered is that pollen is exposed to external influences which can alter its allergenicity. These external influences include environmental factors such as gaseous pollutants like ozone or nitrogen oxides or particulate air pollutants, but also meteorological events like changes in temperature, humidity, or precipitation. In this review, we look at the birch pollen from different angles and summarize current knowledge on internal and external influences that have an impact on the allergenicity of birch pollen and its interactions with the epithelial barrier. We focus on epithelial cells since these cells are the first line of defense in respiratory disease and are increasingly considered to be a regulatory tissue for the protection against the development of respiratory allergies.

Homeologous regulation of Frigida-like genes provides insights on reproductive development and somatic embryogenesis in the allotetraploid Coffea arabica

Coffea arabica is an allotetraploid of high economic importance. C. arabica transcriptome is a combination of the transcripts of two parental genomes (C. eugenioides and C. canephora) that gave rise to the homeologous genes of the species. Previous studies have reported the transcriptional dynamics of C. arabica. In these reports, the ancestry of homeologous genes was identified and the overall regulation of homeologous differential expression (HDE) was explored. One of these genes is part of the FRIGIDA-like family (FRL), which includes the Arabidopsis thaliana flowering-time regulation protein, FRIGIDA (FRI). As nonfunctional FRI proteins give rise to rapid-cycling summer annual ecotypes instead of vernalization-responsive winter-annuals, allelic variation in FRI can modulate flowering time in A. thaliana. Using bioinformatics, genomic analysis, and the evaluation of gene expression of homeologs, we characterized the FRL gene family in C. arabica. Our findings indicate that C. arabica expresses 10 FRL homeologs, and that, throughout flower and fruit development, these genes are differentially transcribed. Strikingly, in addition to confirming the expression of FRL genes during zygotic embryogenesis, we detected FRL expression during direct somatic embryogenesis, a novel finding regarding the FRL gene family. The HDE profile of FRL genes suggests an intertwined homeologous gene regulation. Furthermore, we observed that FLC gene of C. arabica has an expression profile similar to that of CaFRL genes.

Genome-Wide Transcriptional Changes and Lipid Profile Modifications Induced by Medicago truncatula N5 Overexpression at an Early Stage of the Symbiotic Interaction with Sinorhizobium meliloti

Plant lipid-transfer proteins (LTPs) are small basic secreted proteins, which are characterized by lipid-binding capacity and are putatively involved in lipid trafficking. LTPs play a role in several biological processes, including the root nodule symbiosis. In this regard, the Medicago truncatula nodulin 5 (MtN5) LTP has been proved to positively regulate the nodulation capacity, controlling rhizobial infection and nodule primordia invasion. To better define the lipid transfer protein MtN5 function during the symbiosis, we produced MtN5-downregulated and -overexpressing plants, and we analysed the transcriptomic changes occurring in the roots at an early stage of Sinorhizobium meliloti infection. We also carried out the lipid profile analysis of wild type (WT) and MtN5-overexpressing roots after rhizobia infection. The downregulation of MtN5 increased the root hair curling, an early event of rhizobia infection, and concomitantly induced changes in the expression of defence-related genes. On the other hand, MtN5 overexpression favoured the invasion of the nodules by rhizobia and determined in the roots the modulation of genes that are involved in lipid transport and metabolism as well as an increased content of lipids, especially galactolipids that characterize the symbiosome membranes. Our findings suggest the potential participation of LTPs in the synthesis and rearrangement of membranes occurring during the formation of the infection threads and the symbiosome membrane.

Transcriptome Analysis of Leaves, Flowers and Fruits Perisperm of Coffea arabica L. Reveals the Differential Expression of Genes Involved in Raffinose Biosynthesis

Coffea arabica L. is an important crop in several developing countries. Despite its economic importance, minimal transcriptome data are available for fruit tissues, especially during fruit development where several compounds related to coffee quality are produced. To understand the molecular aspects related to coffee fruit and grain development, we report a large-scale transcriptome analysis of leaf, flower and perisperm fruit tissue development. Illumina sequencing yielded 41,881,572 high-quality filtered reads. De novo assembly generated 65,364 unigenes with an average length of 1,264 bp. A total of 24,548 unigenes were annotated as protein coding genes, including 12,560 full-length sequences. In the annotation process, we identified nine candidate genes related to the biosynthesis of raffinose family oligossacarides (RFOs). These sugars confer osmoprotection and are accumulated during initial fruit development. Four genes from this pathway had their transcriptional pattern validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Furthermore, we identified ~24,000 putative target sites for microRNAs (miRNAs) and 134 putative transcriptionally active transposable elements (TE) sequences in our dataset. This C. arabica transcriptomic atlas provides an important step for identifying candidate genes related to several coffee metabolic pathways, especially those related to fruit chemical composition and therefore beverage quality. Our results are the starting point for enhancing our knowledge about the coffee genes that are transcribed during the flowering and initial fruit development stages.

Genomic Identification and Comparative Expansion Analysis of the Non-Specific Lipid Transfer Protein Gene Family in Gossypium

Plant non-specific lipid transfer proteins (nsLTPs) are involved in many biological processes. In this study, 51, 47 and 91 nsLTPs were identified in Gossypium arboreum, G. raimondii and their descendant allotetraploid G. hirsutum, respectively. All the nsLTPs were phylogenetically divided into 8 distinct subfamilies. Besides, the recent duplication, which is considered cotton-specific whole genome duplication, may have led to nsLTP expansion in Gossypium. Both tandem and segmental duplication contributed to nsLTP expansion in G. arboreum and G. hirsutum, while tandem duplication was the dominant pattern in G. raimondii. Additionally, the interspecific orthologous gene pairs in Gossypium were identified. Some GaLTPs and GrLTPs lost their orthologs in the At and Dt subgenomes, respectively, of G. hirsutum. The distribution of these GrLTPs and GaLTPs within each subfamily was complementary, suggesting that the loss and retention of nsLTPs in G. hirsutum might not be random. Moreover, the nsLTPs in the At and Dt subgenomes might have evolved symmetrically. Furthermore, both intraspecific and interspecific orthologous genes showed considerable expression variation, suggesting that their functions were strongly differentiated. Our results lay an important foundation for expansion and evolutionary analysis of the nsLTP family in Gossypium, and advance nsLTP studies in other plants, especially polyploid plants.

Transcriptome analysis in Coffea eugenioides, an Arabica coffee ancestor, reveals differentially expressed genes in leaves and fruits

Studies in diploid parental species of polyploid plants are important to understand their contributions to the formation of plant and species evolution. Coffea eugenioides is a diploid species that is considered to be an ancestor of allopolyploid Coffea arabica together with Coffea canephora. Despite its importance in the evolutionary history of the main economic species of coffee, no study has focused on C. eugenioides molecular genetics. RNA-seq creates the possibility to generate reference transcriptomes and identify coding genes and potential candidates related to important agronomic traits. Therefore, the main objectives were to obtain a global overview of transcriptionally active genes in this species using next-generation sequencing and to analyze specific genes that were highly expressed in leaves and fruits with potential exploratory characteristics for breeding and understanding the evolutionary biology of coffee. A de novo assembly generated 36,935 contigs that were annotated using eight databases. We observed a total of ~5000 differentially expressed genes between leaves and fruits. Several genes exclusively expressed in fruits did not exhibit similarities with sequences in any database. We selected ten differentially expressed unigenes in leaves and fruits to evaluate transcriptional profiles using qPCR. Our study provides the first gene catalog for C. eugenioides and enhances the knowledge concerning the mechanisms involved in the C. arabica homeologous. Furthermore, this work will open new avenues for studies into specific genes and pathways in this species, especially related to fruit, and our data have potential value in assisted breeding applications.