Advancing Eucalyptus genomics: identification and sequencing of lignin biosynthesis genes from deep-coverage BAC libraries

Transcriptome analysis of the transition from primary to secondary growth of vertical stem in Eucalyptus grandis

Eucalyptus was one of the most cultivated hardwood species worldwide, with rapid growth, good wood properties and a wide range of adaptability. Eucalyptus stem undergoes primary growth (longitudinal growth) followed by secondary growth (radial growth), which produces biomass that is an important source of energy worldwide. In order to better understand the genetic regulation of secondary growth in Eucalyptus grandis, Transcriptome analyses in stem segments along a developmental gradient from the third internode to the eleventh internode of E. grandis that spanned primary to secondary growth were carried out. 5,149 genes that were differentially expressed during stem development were identified. Combining the trend analysis by the Mfuzz method and the module-trait correlation analysis by the Weighted Gene Co-expression Network Analysis method, a total of 70 differentially expressed genes (DEGs) selected from 868 DEGs with high connectivity were found to be closely correlated with secondary growth. Results revealed that the differential expression of these DEGs suggests that they may involve in the primary growth or secondary growth. AP1, YAB2 TFs and EXP genes are highly expressed in the IN3, whereas NAC, MYB TFs are likely to be important for secondary growth. These results will expand our understanding of the complex molecular and cellular events of secondary growth and provide a foundation for future studies on wood formation in Eucalyptus.

Identification of WUSCHEL-related homeobox gene and truncated small peptides in transformation efficiency improvement in Eucalyptus

BACKGROUND

The WUSCHEL-related Homeobox (WOX) genes, which encode plant-specific homeobox (HB) transcription factors, play crucial roles in regulating plant growth and development. However, the functions of WOX genes are little known in Eucalyptus, one of the fastest-growing tree resources with considerable widespread cultivation worldwide.

RESULTS

A total of nine WOX genes named EgWOX1-EgWOX9 were retrieved and designated from Eucalyptus grandis. From the three divided clades marked as Modern/WUS, Intermediate and Ancient, the largest group Modern/WUS (6 EgWOXs) contains a specific domain with 8 amino acids: TLQLFPLR. The collinearity, cis-regulatory elements, protein-protein interaction network and gene expression analysis reveal that the WUS proteins in E. grandis involve in regulating meristems development and regeneration. Furthermore, by externally adding of truncated peptides isolated from WUS specific domain, the transformation efficiency in E. urophylla × E. grandis DH32-29 was significant enhanced. The transcriptomics data further reveals that the use of small peptides activates metabolism pathways such as starch and sucrose metabolism, phenylpropanoid biosynthesis and flavonoid biosynthesis.

CONCLUSIONS

Peptides isolated from WUS protein can be utilized to enhance the transformation efficiency in Eucalyptus, thereby contributing to the high-efficiency breeding of Eucalyptus.

Comparison of eight complete chloroplast genomes of the endangered Aquilaria tree species (Thymelaeaceae) and their phylogenetic relationships

Aquilaria tree species are naturally distributed in the Indomalesian region and are protected against over-exploitation. They produce a fragrant non-timber product of high economic value, agarwood. Ambiguous species delimitation and limited genetic information within Aquilaria are among the impediments to conservation efforts. In this study, we conducted comparative analysis on eight Aquilaria species complete chloroplast (cp) genomes, of which seven were newly sequenced using Illumina HiSeq X Ten platform followed by de novo assembly. Aquilaria cp genomes possess a typical quadripartite structure including gene order and genomic structure. The length of each of the cp genome is about 174 kbp and encoded between 89 and 92 proteins, 38 tRNAs, and 8 rRNAs, with 27 duplicated in the IR (inverted repeat) region. Besides, 832 repeats (forward, reverse, palindrome and complement repeats) and nine highly variable regions were also identified. The phylogenetic analysis suggests that the topology structure of Aquilaria cp genomes were well presented with strong support values based on the cp genomes data set and matches their geographic distribution pattern. In summary, the complete cp genomes will facilitate development of species-specific molecular tools to discriminate Aquilaria species and resolve the evolutionary relationships of members of the Thymelaeaceae family.

Landscape drivers of genomic diversity and divergence in woodland Eucalyptus

Spatial genetic patterns are influenced by numerous factors, and they can vary even among coexisting, closely related species due to differences in dispersal and selection. Eucalyptus (L'Héritier 1789; the "eucalypts") are foundation tree species that provide essential habitat and modulate ecosystem services throughout Australia. Here we present a study of landscape genomic variation in two woodland eucalypt species, using whole-genome sequencing of 388 individuals of Eucalyptus albens and Eucalyptus sideroxylon. We found exceptionally high genetic diversity (π ≈ 0.05) and low genome-wide, interspecific differentiation (FST  = 0.15) and intraspecific differentiation between localities (FST  ≈ 0.01-0.02). We found no support for strong, discrete population structure, but found substantial support for isolation by geographic distance (IBD) in both species. Using generalized dissimilarity modelling, we identified additional isolation by environment (IBE). Eucalyptus albens showed moderate IBD, and environmental variables have a small but significant amount of additional predictive power (i.e. IBE). Eucalyptus sideroxylon showed much stronger IBD and moderate IBE. These results highlight the vast adaptive potential of these species and set the stage for testing evolutionary hypotheses of interspecific adaptive differentiation across environments.

Identifying genetic markers for a range of phylogenetic utility-From species to family level

Resolving the phylogenetic relationships of closely related species using a small set of loci is challenging as sufficient information may not be captured from a limited sample of the genome. Relying on few loci can also be problematic when conflict between gene-trees arises from incomplete lineage sorting and/or ongoing hybridization, problems especially likely in recently diverged lineages. Here, we developed a method using limited genomic resources that allows identification of many low copy candidate loci from across the nuclear and chloroplast genomes, design probes for target capture and sequence the captured loci. To validate our method we present data from Eucalyptus and Melaleuca, two large and phylogenetically problematic genera within the Myrtaceae family. With one annotated genome, one transcriptome and two whole-genome shotgun sequences of one Eucalyptus and four Melaleuca species, respectively, we identified 212 loci representing 263 kbp for targeted sequence capture and sequencing. Of these, 209 were successfully tested from 47 samples across five related genera of Myrtaceae. The average percentage of reads mapped back to the reference was 57.6% with coverage of more than 20 reads per position across 83.5% of the data. The methods developed here should be applicable across a large range of taxa across all kingdoms. The core methods are very flexible, providing a platform for various genomic resource availabilities and are useful from shallow to deep phylogenies.

Comprehensive Analysis of Rhodomyrtus tomentosa Chloroplast Genome

In the last decade, several studies have relied on a small number of plastid genomes to deduce deep phylogenetic relationships in the species-rich Myrtaceae. Nevertheless, the plastome of Rhodomyrtus tomentosa, an important representative plant of the Rhodomyrtus (DC.) genera, has not yet been reported yet. Here, we sequenced and analyzed the complete chloroplast (CP) genome of R. tomentosa, which is a 156,129-bp-long circular molecule with 37.1% GC content. This CP genome displays a typical quadripartite structure with two inverted repeats (IRa and IRb), of 25,824 bp each, that are separated by a small single copy region (SSC, 18,183 bp) and one large single copy region (LSC, 86,298 bp). The CP genome encodes 129 genes, including 84 protein-coding genes, 37 tRNA genes, eight rRNA genes and three pseudogenes (ycf1, rps19, ndhF). A considerable number of protein-coding genes have a universal ATG start codon, except for psbL and ndhD. Premature termination codons (PTCs) were found in one protein-coding gene, namely atpE, which is rarely reported in the CP genome of plants. Phylogenetic analysis revealed that R. tomentosa has a sister relationship with Eugenia uniflora and Psidium guajava. In conclusion, this study identified unique characteristics of the R. tomentosa CP genome providing valuable information for further investigations on species identification and the phylogenetic evolution between R. tomentosa and related species.

The Koala (Phascolarctos cinereus) faecal microbiome differs with diet in a wild population

Background

The diet of the koala (Phascolarctos cinereus) is comprised almost exclusively of foliage from the genus Eucalyptus (family Myrtaceae). Eucalyptus produces a wide variety of potentially toxic plant secondary metabolites which have evolved as chemical defences against herbivory. The koala is classified as an obligate dietary specialist, and although dietary specialisation is rare in mammalian herbivores, it has been found elsewhere to promote a highly-conserved but low-diversity gut microbiome. The gut microbes of dietary specialists have been found sometimes to enhance tolerance of dietary PSMs, facilitating competition-free access to food. Although the koala and its gut microbes have evolved together to utilise a low nutrient, potentially toxic diet, their gut microbiome has not previously been assessed in conjunction with diet quality. Thus, linking the two may provide new insights in to the ability of the koala to extract nutrients and detoxify their potentially toxic diet.

Method

The 16S rRNA gene was used to characterise the composition and diversity of faecal bacterial communities from a wild koala population (n = 32) comprising individuals that predominately eat either one of two different food species, one the strongly preferred and relatively nutritious species Eucalyptus viminalis, the other comprising the less preferred and less digestible species Eucalyptus obliqua.

Results

Alpha diversity indices indicated consistently and significantly lower diversity and richness in koalas eating E. viminalis. Assessment of beta diversity using both weighted and unweighted UniFrac matrices indicated that diet was a strong driver of both microbial community structure, and of microbial presence/absence across the combined koala population and when assessed independently. Further, principal coordinates analysis based on both the weighted and unweighted UniFrac matrices for the combined and separated populations, also revealed a separation linked to diet. During our analysis of the OTU tables we also detected a strong association between microbial community composition and host diet. We found that the phyla Bacteroidetes and Firmicutes were co-dominant in all faecal microbiomes, with Cyanobacteria also co-dominant in some individuals; however, the E. viminalis diet produced communities dominated by the genera Parabacteroides and/or Bacteroides, whereas the E. obliqua-associated diets were dominated by unidentified genera from the family Ruminococcaceae.

Discussion

We show that diet differences, even those caused by differential consumption of the foliage of two species from the same plant genus, can profoundly affect the gut microbiome of a specialist folivorous mammal, even amongst individuals in the same population. We identify key microbiota associated with each diet type and predict functions within the microbial community based on 80 previously identified Parabacteroides and Ruminococcaceae genomes.

The plastid and mitochondrial genomes of Eucalyptus grandis

BACKGROUND

Land plant organellar genomes have significant impact on metabolism and adaptation, and as such, accurate assembly and annotation of plant organellar genomes is an important tool in understanding the evolutionary history and interactions between these genomes. Intracellular DNA transfer is ongoing between the nuclear and organellar genomes, and can lead to significant genomic variation between, and within, species that impacts downstream analysis of genomes and transcriptomes.

RESULTS

In order to facilitate further studies of cytonuclear interactions in Eucalyptus, we report an updated annotation of the E. grandis plastid genome, and the second sequenced and annotated mitochondrial genome of the Myrtales, that of E. grandis. The 478,813 bp mitochondrial genome shows the conserved protein coding regions and gene order rearrangements typical of land plants. There have been widespread insertions of organellar DNA into the E. grandis nuclear genome, which span 141 annotated nuclear genes. Further, we identify predicted editing sites to allow for the discrimination of RNA-sequencing reads between nuclear and organellar gene copies, finding that nuclear copies of organellar genes are not expressed in E. grandis.

CONCLUSIONS

The implications of organellar DNA transfer to the nucleus are often ignored, despite the insight they can give into the ongoing evolution of plant genomes, and the problems they can cause in many applications of genomics. Future comparisons of the transcription and regulation of organellar genes between Eucalyptus genotypes may provide insight to the cytonuclear interactions that impact economically important traits in this widely grown lignocellulosic crop species.

Genomic Prediction of Growth and Stem Quality Traits in Eucalyptus globulus Labill. at Its Southernmost Distribution Limit in Chile

The present study was undertaken to examine the ability of different genomic selection (GS) models to predict growth traits (diameter at breast height, tree height and wood volume), stem straightness and branching quality of Eucalyptus globulus Labill. trees using a genome-wide Single Nucleotide Polymorphism (SNP) chip (60 K), in one of the southernmost progeny trials of the species, close to its southern distribution limit in Chile. The GS methods examined were Ridge Regression-BLUP (RRBLUP), Bayes-A, Bayes-B, Bayesian least absolute shrinkage and selection operator (BLASSO), principal component regression (PCR), supervised PCR and a variant of the RRBLUP method that involves the previous selection of predictor variables (RRBLUP-B). RRBLUP-B and supervised PCR models presented the greatest predictive ability (PA), followed by the PCR method, for most of the traits studied. The highest PA was obtained for the branching quality (~0.7). For the growth traits, the maximum values of PA varied from 0.43 to 0.54, while for stem straightness, the maximum value of PA reached 0.62 (supervised PCR). The study population presented a more extended linkage disequilibrium (LD) than other populations of E. globulus previously studied. The genome-wide LD decayed rapidly within 0.76 Mbp (threshold value of r2 = 0.1). The average LD on all chromosomes was r2 = 0.09. In addition, the 0.15% of total pairs of linked SNPs were in a complete LD (r2 = 1), and the 3% had an r2 value >0.5. Genomic prediction, which is based on the reduction in dimensionality and variable selection may be a promising method, considering the early growth of the trees and the low-to-moderate values of heritability found in the traits evaluated. These findings provide new understanding of how develop novel breeding strategies for tree improvement of E. globulus at its southernmost range limit in Chile, which could represent new opportunities for forest planting that can benefit the local economy.

EUCANEXT: an integrated database for the exploration of genomic and transcriptomic data from Eucalyptus species

Tree species of the genus Eucalyptus are the most valuable and widely planted hardwoods in the world. Given the economic importance of Eucalyptus trees, much effort has been made towards the generation of specimens with superior forestry properties that can deliver high-quality feedstocks, customized to the industrýs needs for both cellulosic (paper) and lignocellulosic biomass production. In line with these efforts, large sets of molecular data have been generated by several scientific groups, providing invaluable information that can be applied in the development of improved specimens. In order to fully explore the potential of available datasets, the development of a public database that provides integrated access to genomic and transcriptomic data from Eucalyptus is needed. EUCANEXT is a database that analyses and integrates publicly available Eucalyptus molecular data, such as the E. grandis genome assembly and predicted genes, ESTs from several species and digital gene expression from 26 RNA-Seq libraries. The database has been implemented in a Fedora Linux machine running MySQL and Apache, while Perl CGI was used for the web interfaces. EUCANEXT provides a user-friendly web interface for easy access and analysis of publicly available molecular data from Eucalyptus species. This integrated database allows for complex searches by gene name, keyword or sequence similarity and is publicly accessible at http://www.lge.ibi.unicamp.br/eucalyptusdb. Through EUCANEXT, users can perform complex analysis to identify genes related traits of interest using RNA-Seq libraries and tools for differential expression analysis. Moreover, all the bioinformatics pipeline here described, including the database schema and PERL scripts, are readily available and can be applied to any genomic and transcriptomic project, regardless of the organism.

Database URL:http://www.lge.ibi.unicamp.br/eucalyptusdb

Effective BAC clone anchoring with genotyping-by-sequencing and Diversity Arrays Technology in a large genome cereal rye

Identification of bacterial artificial chromosome (BAC) clones containing specific sequences is a prerequisite for many applications, such as physical map anchoring or gene cloning. Existing BAC library screening strategies are either low-throughput or require a considerable initial input of resources for platform establishment. We describe a high-throughput, reliable, and cost-effective BAC library screening approach deploying genotyping platforms which are independent from the availability of sequence information: a genotyping-by-sequencing (GBS) method DArTSeq and the microarray-based Diversity Arrays Technology (DArT). The performance of these methods was tested in a very large and complex rye genome. The DArTseq approach delivered superior results: a several fold higher efficiency of addressing genetic markers to BAC clones and anchoring of BAC clones to genetic map and also a higher reliability. Considering the sequence independence of the platform, the DArTseq-based library screening can be proposed as an attractive method to speed up genomics research in resource poor species.

Chloroplast variation is incongruent with classification of the Australian bloodwood eucalypts (genus Corymbia, family Myrtaceae)

Previous molecular phylogenetic analyses have resolved the Australian bloodwood eucalypt genus Corymbia (~100 species) as either monophyletic or paraphyletic with respect to Angophora (9-10 species). Here we assess relationships of Corymbia and Angophora using a large dataset of chloroplast DNA sequences (121,016 base pairs; from 90 accessions representing 55 Corymbia and 8 Angophora species, plus 33 accessions of related genera), skimmed from high throughput sequencing of genomic DNA, and compare results with new analyses of nuclear ITS sequences (119 accessions) from previous studies. Maximum likelihood and maximum parsimony analyses of cpDNA resolve well supported trees with most nodes having >95% bootstrap support. These trees strongly reject monophyly of Corymbia, its two subgenera (Corymbia and Blakella), most taxonomic sections (Abbreviatae, Maculatae, Naviculares, Septentrionales), and several species. ITS trees weakly indicate paraphyly of Corymbia (bootstrap support <50% for maximum likelihood, and 71% for parsimony), but are highly incongruent with the cpDNA analyses, in that they support monophyly of both subgenera and some taxonomic sections of Corymbia. The striking incongruence between cpDNA trees and both morphological taxonomy and ITS trees is attributed largely to chloroplast introgression between taxa, because of geographic sharing of chloroplast clades across taxonomic groups. Such introgression has been widely inferred in studies of the related genus Eucalyptus. This is the first report of its likely prevalence in Corymbia and Angophora, but this is consistent with previous morphological inferences of hybridisation between species. Our findings (based on continent-wide sampling) highlight a need for more focussed studies to assess the extent of hybridisation and introgression in the evolutionary history of these genera, and that critical testing of the classification of Corymbia and Angophora requires additional sequence data from nuclear genomes.

Advancing Eucalyptus Genomics: Cytogenomics Reveals Conservation of Eucalyptus Genomes

The genus Eucalyptus encloses several species with high ecological and economic value, being the subgenus Symphyomyrtus one of the most important. Species such as E. grandis and E. globulus are well characterized at the molecular level but knowledge regarding genome and chromosome organization is very scarce. Here we characterized and compared the karyotypes of three economically important species, E. grandis, E. globulus, and E. calmadulensis, and three with ecological relevance, E. pulverulenta, E. cornuta, and E. occidentalis, through an integrative approach including genome size estimation, fluorochrome banding, rDNA FISH, and BAC landing comprising genes involved in lignin biosynthesis. All karyotypes show a high degree of conservation with pericentromeric 35S and 5S rDNA loci in the first and third pairs, respectively. GC-rich heterochromatin was restricted to the 35S rDNA locus while the AT-rich heterochromatin pattern was species-specific. The slight differences in karyotype formulas and distribution of AT-rich heterochromatin, along with genome sizes estimations, support the idea of Eucalyptus genome evolution by local expansions of heterochromatin clusters. The unusual co-localization of both rDNA with AT-rich heterochromatin was attributed mainly to the presence of silent transposable elements in those loci. The cinnamoyl CoA reductase gene (CCR1) previously assessed to linkage group 10 (LG10) was clearly localized distally at the long arm of chromosome 9 establishing an unexpected correlation between the cytogenetic chromosome 9 and the LG10. Our work is novel and contributes to the understanding of Eucalyptus genome organization which is essential to develop successful advanced breeding strategies for this genus.

Genome-wide analysis of the lignin toolbox of Eucalyptus grandis

Lignin, a major component of secondary cell walls, hinders the optimal processing of wood for industrial uses. The recent availability of the Eucalyptus grandis genome sequence allows comprehensive analysis of the genes encoding the 11 protein families specific to the lignin branch of the phenylpropanoid pathway and identification of those mainly involved in xylem developmental lignification. We performed genome-wide identification of putative members of the lignin gene families, followed by comparative phylogenetic studies focusing on bona fide clades inferred from genes functionally characterized in other species. RNA-seq and microfluid real-time quantitative PCR (RT-qPCR) expression data were used to investigate the developmental and environmental responsive expression patterns of the genes. The phylogenetic analysis revealed that 38 E. grandis genes are located in bona fide lignification clades. Four multigene families (shikimate O-hydroxycinnamoyltransferase (HCT), p-coumarate 3-hydroxylase (C3H), caffeate/5-hydroxyferulate O-methyltransferase (COMT) and phenylalanine ammonia-lyase (PAL)) are expanded by tandem gene duplication compared with other plant species. Seventeen of the 38 genes exhibited strong, preferential expression in highly lignified tissues, probably representing the E. grandis core lignification toolbox. The identification of major genes involved in lignin biosynthesis in E. grandis, the most widely planted hardwood crop world-wide, provides the foundation for the development of biotechnology approaches to develop tree varieties with enhanced processing qualities.

Development of genetic markers in Eucalyptus species by target enrichment and exome sequencing

The advent of next-generation sequencing has facilitated large-scale discovery, validation and assessment of genetic markers for high density genotyping. The present study was undertaken to identify markers in genes supposedly related to wood property traits in three Eucalyptus species. Ninety four genes involved in xylogenesis were selected for hybridization probe based nuclear genomic DNA target enrichment and exome sequencing. Genomic DNA was isolated from the leaf tissues and used for on-array probe hybridization followed by Illumina sequencing. The raw sequence reads were trimmed and high-quality reads were mapped to the E. grandis reference sequence and the presence of single nucleotide variants (SNVs) and insertions/ deletions (InDels) were identified across the three species. The average read coverage was 216X and a total of 2294 SNVs and 479 InDels were discovered in E. camaldulensis, 2383 SNVs and 518 InDels in E. tereticornis, and 1228 SNVs and 409 InDels in E. grandis. Additionally, SNV calling and InDel detection were conducted in pair-wise comparisons of E. tereticornis vs. E. grandis, E. camaldulensis vs. E. tereticornis and E. camaldulensis vs. E. grandis. This study presents an efficient and high throughput method on development of genetic markers for family– based QTL and association analysis in Eucalyptus.

Structure, expression profile and phylogenetic inference of chalcone isomerase-like genes from the narrow-leafed lupin (Lupinus angustifolius L.) genome

Lupins, like other legumes, have a unique biosynthesis scheme of 5-deoxy-type flavonoids and isoflavonoids. A key enzyme in this pathway is chalcone isomerase (CHI), a member of CHI-fold protein family, encompassing subfamilies of CHI1, CHI2, CHI-like (CHIL), and fatty acid-binding (FAP) proteins. Here, two Lupinus angustifolius (narrow-leafed lupin) CHILs, LangCHIL1 and LangCHIL2, were identified and characterized using DNA fingerprinting, cytogenetic and linkage mapping, sequencing and expression profiling. Clones carrying CHIL sequences were assembled into two contigs. Full gene sequences were obtained from these contigs, and mapped in two L. angustifolius linkage groups by gene-specific markers. Bacterial artificial chromosome fluorescence in situ hybridization approach confirmed the localization of two LangCHIL genes in distinct chromosomes. The expression profiles of both LangCHIL isoforms were very similar. The highest level of transcription was in the roots of the third week of plant growth; thereafter, expression declined. The expression of both LangCHIL genes in leaves and stems was similar and low. Comparative mapping to reference legume genome sequences revealed strong syntenic links; however, LangCHIL2 contig had a much more conserved structure than LangCHIL1. LangCHIL2 is assumed to be an ancestor gene, whereas LangCHIL1 probably appeared as a result of duplication. As both copies are transcriptionally active, questions arise concerning their hypothetical functional divergence. Screening of the narrow-leafed lupin genome and transcriptome with CHI-fold protein sequences, followed by Bayesian inference of phylogeny and cross-genera synteny survey, identified representatives of all but one (CHI1) main subfamilies. They are as follows: two copies of CHI2, FAPa2 and CHIL, and single copies of FAPb and FAPa1. Duplicated genes are remnants of whole genome duplication which is assumed to have occurred after the divergence of Lupinus, Arachis, and Glycine.

Microsatellite resources of Eucalyptus: current status and future perspectives

Eucalyptus is the premier paper pulp, short rotation plantation species grown all over the world. Genetic improvement programs integrating molecular marker tools are in progress in many parts of the globe to increase the productivity. Whole genome sequence and expressed sequence tags (ESTs) of the eucalypts paved way for introduction of molecular genetics and breeding in this genus. Different molecular characterization approaches have been used simultaneously in eucalypts, however, microsatellites or simple sequence repeats (SSRs) with their prolific characteristics could occupy a special niche in Eucalyptus genetic improvement. Further, highly informative SSRs were used for the clonal identity, genetic fidelity and in certification of breeder's rights. Eucalyptus genetic linkage maps generated with microsatellite loci were used successfully to identify quantitative trait loci (QTLs) for various economically important traits. Progressively more numbers of microsatellites are being linked to genes associated with adaptive and functional variations, therefore making their utility broader in genetic applications. Availability of common SSR markers across the species provides an opportunity to validate the expression of QTLs across variable genetic backgrounds and accurately compare the position of QTLs in other species. Recent evidences suggest that the presence of SSRs in micro RNAs of plant species play a role in the quantitative trait expression. Similar studies in eucalypts may provide new insights into the genetic architecture of transcript-level variations and post transcriptional gene regulation. This review on eucalypts microsatellites, highlights the availability and characteristics of genomic and eSSRs and their potential in genetic analysis of natural and breeding populations and also discusses the future prospects in population genetics and marker assisted selection.

Flavonoid supplementation affects the expression of genes involved in cell wall formation and lignification metabolism and increases sugar content and saccharification in the fast-growing eucalyptus hybrid E. urophylla x E. grandis

BACKGROUND

Eucalyptus species are the most widely planted hardwood species in the world and are renowned for their rapid growth and adaptability. In Brazil, one of the most widely grown Eucalyptus cultivars is the fast-growing Eucalyptus urophylla x Eucalyptus grandis hybrid. In a previous study, we described a chemical characterization of these hybrids when subjected to flavonoid supplementation on 2 distinct timetables, and our results revealed marked differences between the wood composition of the treated and untreated trees.

RESULTS

In this work, we report the transcriptional responses occurring in these trees that may be related to the observed chemical differences. Gene expression was analysed through mRNA-sequencing, and notably, compared to control trees, the treated trees display differential down-regulation of cell wall formation pathways such as phenylpropanoid metabolism as well as differential expression of genes involved in sucrose, starch and minor CHO metabolism and genes that play a role in several stress and environmental responses. We also performed enzymatic hydrolysis of wood samples from the different treatments, and the results indicated higher sugar contents and glucose yields in the flavonoid-treated plants.

CONCLUSIONS

Our results further illustrate the potential use of flavonoids as a nutritional complement for modifying Eucalyptus wood, since, supplementation with flavonoids alters its chemical composition, gene expression and increases saccharification probably as part of a stress response.

Begin at the beginning: A BAC-end view of the passion fruit (Passiflora) genome

Background

The passion fruit (Passiflora edulis) is a tropical crop of economic importance both for juice production and consumption as fresh fruit. The juice is also used in concentrate blends that are consumed worldwide. However, very little is known about the genome of the species. Therefore, improving our understanding of passion fruit genomics is essential and to some degree a pre-requisite if its genetic resources are to be used more efficiently. In this study, we have constructed a large-insert BAC library and provided the first view on the structure and content of the passion fruit genome, using BAC-end sequence (BES) data as a major resource.

Results

The library consisted of 82,944 clones and its levels of organellar DNA were very low. The library represents six haploid genome equivalents, and the average insert size was 108 kb. To check its utility for gene isolation, successful macroarray screening experiments were carried out with probes complementary to eight Passiflora gene sequences available in public databases. BACs harbouring those genes were used in fluorescent in situ hybridizations and unique signals were detected for four BACs in three chromosomes (n = 9). Then, we explored 10,000 BES and we identified reads likely to contain repetitive mobile elements (19.6% of all BES), simple sequence repeats and putative proteins, and to estimate the GC content (~42%) of the reads. Around 9.6% of all BES were found to have high levels of similarity to plant genes and ontological terms were assigned to more than half of the sequences analysed (940). The vast majority of the top-hits made by our sequences were to Populus trichocarpa (24.8% of the total occurrences), Theobroma cacao (21.6%), Ricinus communis (14.3%), Vitis vinifera (6.5%) and Prunus persica (3.8%).

Conclusions

We generated the first large-insert library for a member of Passifloraceae. This BAC library provides a new resource for genetic and genomic studies, as well as it represents a valuable tool for future whole genome study. Remarkably, a number of BAC-end pair sequences could be mapped to intervals of the sequenced Arabidopsis thaliana, V. vinifera and P. trichocarpa chromosomes, and putative collinear microsyntenic regions were identified.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-816) contains supplementary material, which is available to authorized users.

A genomics approach to deciphering lignin biosynthesis in switchgrass

It is necessary to overcome recalcitrance of the biomass to saccharification (sugar release) to make switchgrass (Panicum virgatum) economically viable as a feedstock for liquid biofuels. Lignin content correlates negatively with sugar release efficiency in switchgrass, but selecting the right gene candidates for engineering lignin biosynthesis in this tetraploid outcrossing species is not straightforward. To assist this endeavor, we have used an inducible switchgrass cell suspension system for studying lignin biosynthesis in response to exogenous brassinolide. By applying a combination of protein sequence phylogeny with whole-genome microarray analyses of induced cell cultures and developing stem internode sections, we have generated a list of candidate monolignol biosynthetic genes for switchgrass. Several genes that were strongly supported through our bioinformatics analysis as involved in lignin biosynthesis were confirmed by gene silencing studies, in which lignin levels were reduced as a result of targeting a single gene. However, candidate genes encoding enzymes involved in the early steps of the currently accepted monolignol biosynthesis pathway in dicots may have functionally redundant paralogues in switchgrass and therefore require further evaluation. This work provides a blueprint and resources for the systematic genome-wide study of the monolignol pathway in switchgrass, as well as other C4 monocot species.

Open access to tree genomes: the path to a better forest

An open-access culture and a well-developed comparative-genomics infrastructure must be developed in forest trees to derive the full potential of genome sequencing in this diverse group of plants that are the dominant species in much of the earth's terrestrial ecosystems.

Xylem transcription profiles indicate potential metabolic responses for economically relevant characteristics of Eucalyptus species

Background

Eucalyptus is one of the most important sources of industrial cellulose. Three species of this botanical group are intensively used in breeding programs: E. globulus, E. grandis and E. urophylla. E. globulus is adapted to subtropical/temperate areas and is considered a source of high-quality cellulose; E. grandis grows rapidly and is adapted to tropical/subtropical climates; and E. urophylla, though less productive, is considered a source of genes related to robustness. Wood, or secondary xylem, results from cambium vascular differentiation and is mostly composed of cellulose, lignin and hemicelluloses. In this study, the xylem transcriptomes of the three Eucalyptus species were investigated in order to provide insights on the particularities presented by each of these species.

Results

Data analysis showed that (1) most Eucalyptus genes are expressed in xylem; (2) most genes expressed in species-specific way constitutes genes with unknown functions and are interesting targets for future studies; (3) relevant differences were observed in the phenylpropanoid pathway: E. grandis xylem presents higher expression of genes involved in lignin formation whereas E. urophylla seems to deviates the pathway towards flavonoid formation; (4) stress-related genes are considerably more expressed in E. urophylla, suggesting that these genes may contribute to its robustness.

Conclusions

The comparison of these three transcriptomes indicates the molecular signatures underlying some of their distinct wood characteristics. This information may contribute to the understanding of xylogenesis, thus increasing the potential of genetic engineering approaches aiming at the improvement of Eucalyptus forest plantations productivity.

Reference genes for high-throughput quantitative reverse transcription-PCR analysis of gene expression in organs and tissues of Eucalyptus grown in various environmental conditions

Interest in the genomics of Eucalyptus has skyrocketed thanks to the recent sequencing of the genome of Eucalyptus grandis and to a growing number of large-scale transcriptomic studies. Quantitative reverse transcription-PCR (RT-PCR) is the method of choice for gene expression analysis and can now also be used as a high-throughput method. The selection of appropriate internal controls is becoming of utmost importance to ensure accurate expression results in Eucalyptus. To this end, we selected 21 candidate reference genes and used high-throughput microfluidic dynamic arrays to assess their expression among a large panel of developmental and environmental conditions with a special focus on wood-forming tissues. We analyzed the expression stability of these genes by using three distinct statistical algorithms (geNorm, NormFinder and ΔCt), and used principal component analysis to compare methods and rankings. We showed that the most stable genes identified depended not only on the panel of biological samples considered but also on the statistical method used. We then developed a comprehensive integration of the rankings generated by the three methods and identified the optimal reference genes for 17 distinct experimental sets covering 13 organs and tissues, as well as various developmental and environmental conditions. The expression patterns of Eucalyptus master genes EgMYB1 and EgMYB2 experimentally validated our selection. Our findings provide an important resource for the selection of appropriate reference genes for accurate and reliable normalization of gene expression data in the organs and tissues of Eucalyptus trees grown in a range of conditions including abiotic stresses.

Biotechnologies for the management of genetic resources for food and agriculture

In recent years, the land area under agriculture has declined as also has the rate of growth in agricultural productivity while the demand for food continues to escalate. The world population now stands at 7 billion and is expected to reach 9 billion in 2045. A broad range of agricultural genetic diversity needs to be available and utilized in order to feed this growing population. Climate change is an added threat to biodiversity that will significantly impact genetic resources for food and agriculture (GRFA) and food production. There is no simple, all-encompassing solution to the challenges of increasing productivity while conserving genetic diversity. Sustainable management of GRFA requires a multipronged approach, and as outlined in the paper, biotechnologies can provide powerful tools for the management of GRFA. These tools vary in complexity from those that are relatively simple to those that are more sophisticated. Further, advances in biotechnologies are occurring at a rapid pace and provide novel opportunities for more effective and efficient management of GRFA. Biotechnology applications must be integrated with ongoing conventional breeding and development programs in order to succeed. Additionally, the generation, adaptation, and adoption of biotechnologies require a consistent level of financial and human resources and appropriate policies need to be in place. These issues were also recognized by Member States at the FAO international technical conference on Agricultural Biotechnologies for Developing Countries (ABDC-10), which took place in March 2010 in Mexico. At the end of the conference, the Member States reached a number of key conclusions, agreeing, inter alia, that developing countries should significantly increase sustained investments in capacity building and the development and use of biotechnologies to maintain the natural resource base; that effective and enabling national biotechnology policies and science-based regulatory frameworks can facilitate the development and appropriate use of biotechnologies in developing countries; and that FAO and other relevant international organizations and donors should significantly increase their efforts to support the strengthening of national capacities in the development and appropriate use of pro-poor agricultural biotechnologies.