Comparative analysis of plant carbohydrate active enZymes and their role in xylogenesis.

BACKGROUND: Carbohydrate metabolism is a key feature of vascular plant architecture, and is of particular importance in large woody species, where lignocellulosic biomass is responsible for bearing the bulk of the stem and crown. Since Carbohydrate Active enZymes (CAZymes) in plants are responsible for the synthesis, modification and degradation of carbohydrate biopolymers, the differences in gene copy number and regulation between woody and herbaceous species have been highlighted previously. There are still many unanswered questions about the role of CAZymes in land plant evolution and the formation of wood, a strong carbohydrate sink. RESULTS: Here, twenty-two publically available plant genomes were used to characterize the frequency, diversity and complexity of CAZymes in plants. We find that a conserved suite of CAZymes is a feature of land plant evolution, with similar diversity and complexity regardless of growth habit and form. In addition, we compared the diversity and levels of CAZyme gene expression during wood formation in trees using mRNA-seq data from two distantly related angiosperm tree species Eucalyptus grandis and Populus trichocarpa, highlighting the major CAZyme classes involved in xylogenesis and lignocellulosic biomass production. CONCLUSIONS: CAZyme domain ratio across embryophytes is maintained, and the diversity of CAZyme domains is similar in all land plants, regardless of woody habit. The stoichiometric conservation of gene expression in woody and non-woody tissues of Eucalyptus and Populus are indicative of gene balance preservation.

Protein domain evolution is associated with reproductive diversification and adaptive radiation in the genus Eucalyptus.

Eucalyptus is a pivotal genus within the rosid order Myrtales with distinct geographic history and adaptations. Comparative analysis of protein domain evolution in the newly sequenced Eucalyptus grandis genome and other rosid lineages sheds light on the adaptive mechanisms integral to the success of this genus of woody perennials. We reconstructed the ancestral domain content to elucidate the gain, loss and expansion of protein domains and domain arrangements in Eucalyptus in the context of rosid phylogeny. We used functional gene ontology (GO) annotation of genes to investigate the possible biological and evolutionary consequences of protein domain expansion. We found that protein modulation within the angiosperms occurred primarily on the level of expansion of certain domains and arrangements. Using RNA-Seq data from E. grandis, we showed that domain expansions have contributed to tissue-specific expression of tandemly duplicated genes. Our results indicate that tandem duplication of genes, a key feature of the Eucalyptus genome, has played an important role in the expansion of domains, particularly in proteins related to the specialization of reproduction and biotic and abiotic interactions affecting root and floral biology, and that tissue-specific expression of proteins with expanded domains has facilitated subfunctionalization in domain families.

The genome of Eucalyptus grandis.

Eucalypts are the world's most widely planted hardwood trees. Their outstanding diversity, adaptability and growth have made them a global renewable resource of fibre and energy. We sequenced and assembled >94% of the 640-megabase genome of Eucalyptus grandis. Of 36,376 predicted protein-coding genes, 34% occur in tandem duplications, the largest proportion thus far in plant genomes. Eucalyptus also shows the highest diversity of genes for specialized metabolites such as terpenes that act as chemical defence and provide unique pharmaceutical oils. Genome sequencing of the E. grandis sister species E. globulus and a set of inbred E. grandis tree genomes reveals dynamic genome evolution and hotspots of inbreeding depression. The E. grandis genome is the first reference for the eudicot order Myrtales and is placed here sister to the eurosids. This resource expands our understanding of the unique biology of large woody perennials and provides a powerful tool to accelerate comparative biology, breeding and biotechnology.

Adjustments in epidermal UV-transmittance of leaves in sun-shade transitions.

Epidermal UV transmittance (TUV ) and UV-absorbing compounds were measured in sun and shade leaves of Populus tremuloides and Vicia faba exposed to contrasting light environments under field conditions to evaluate UV acclimation potentials and regulatory roles of photosynthetically active radiation (PAR) and UV in UV-shielding. Within a natural canopy of P. tremuloides, TUV ranged from 4 to 98% and showed a strong nonlinear relationship with mid-day horizontal fluxes of PAR [photon flux density (PFD) = 6-1830 µmol m⁻² s⁻¹]; similar patterns were found for V. faba leaves that developed under a comparable PFD range. A series of field transfer experiments using neutral-density shade cloth and UV blocking/transmitting films indicated that PAR influenced TUV during leaf development to a greater degree than UV, and shade leaves of both species increased their UV-shielding when exposed to full sun; however, this required the presence of UV, with both UV-A and UV-B required for full acclimation. TUV of sun leaves of both species was largely unresponsive to shade either with or without UV. In most, but not all cases, changes in TUV were associated with alterations in the concentration of whole-leaf UV-absorbing compounds. These results suggest that, (1) moderate-to-high levels of PAR alone during leaf development can induce substantial UV-protection in field-grown plants, (2) mature shade leaves have the potential to adjust their UV-shielding which may reduce the detrimental effects of UV that could occur following sudden exposures to high light and (3) under field conditions, PAR and UV play different roles in regulating UV-shielding during and after leaf development.

Dynamics and adaptive benefits of protein domain emergence and arrangements during plant genome evolution.

Plant genomes are generally very large, mostly paleopolyploid, and have numerous gene duplicates and complex genomic features such as repeats and transposable elements. Many of these features have been hypothesized to enable plants, which cannot easily escape environmental challenges, to rapidly adapt. Another mechanism, which has recently been well described as a major facilitator of rapid adaptation in bacteria, animals, and fungi but not yet for plants, is modular rearrangement of protein-coding genes. Due to the high precision of profile-based methods, rearrangements can be well captured at the protein level by characterizing the emergence, loss, and rearrangements of protein domains, their structural, functional, and evolutionary building blocks. Here, we study the dynamics of domain rearrangements and explore their adaptive benefit in 27 plant and 3 algal genomes. We use a phylogenomic approach by which we can explain the formation of 88% of all arrangements by single-step events, such as fusion, fission, and terminal loss of domains. We find many domains are lost along every lineage, but at least 500 domains are novel, that is, they are unique to green plants and emerged more or less recently. These novel domains duplicate and rearrange more readily within their genomes than ancient domains and are overproportionally involved in stress response and developmental innovations. Novel domains more often affect regulatory proteins and show a higher degree of structural disorder than ancient domains. Whereas a relatively large and well-conserved core set of single-domain proteins exists, long multi-domain arrangements tend to be species-specific. We find that duplicated genes are more often involved in rearrangements. Although fission events typically impact metabolic proteins, fusion events often create new signaling proteins essential for environmental sensing. Taken together, the high volatility of single domains and complex arrangements in plant genomes demonstrate the importance of modularity for environmental adaptability of plants.