title: Medium term water deficit elicits distinct transcriptome responses in Eucalyptus species of contrasting environmental origin.
abstract: Climatic and edaphic conditions over geological timescales have generated enormous diversity of adaptive traits and high speciation within the genus Eucalyptus (L. Hér.). Eucalypt species occur from high rainfall to semi-arid zones and from the tropics to latitudes as high as 43°S. Despite several morphological and metabolomic characterizations, little is known regarding gene expression differences that underpin differences in tolerance to environmental change. Using species of contrasting taxonomy, morphology and physiology (E. globulus and E. cladocalyx), this study combines physiological characterizations with 'second-generation' sequencing to identify key genes involved in eucalypt responses to medium-term water limitation.
  
  
  
  One hundred twenty Million high-quality HiSeq reads were created from 14 tissue samples in plants that had been successfully subjected to a water deficit treatment or a well-watered control. Alignment to the E. grandis genome saw 23,623 genes of which 468 exhibited differential expression (FDR < 0.01) in one or both ecotypes in response to the treatment. Further analysis identified 80 genes that demonstrated a significant species-specific response of which 74 were linked to the 'dry' species E. cladocalyx where 23 of these genes were uncharacterised. The majority (approximately 80%) of these differentially expressed genes, were expressed in stem tissue. Key genes that differentiated species responses were linked to photoprotection/redox balance, phytohormone/signalling, primary photosynthesis/cellular metabolism and secondary metabolism based on plant metabolic pathway network analysis.
  
  
  
  These results highlight a more definitive response to water deficit by a 'dry' climate eucalypt, particularly in stem tissue, identifying key pathways and associated genes that are responsible for the differences between 'wet' and 'dry' climate eucalypts. This knowledge provides the opportunity to further investigate and understand the mechanisms and genetic variation linked to this important environmental response that will assist with genomic efforts in managing native populations as well as in tree improvement programs under future climate scenarios.
authors.affiliation: School of Ecosystem and Forest Sciences, University of Melbourne, Creswick, Victoria, 3363, Australia. avjs@unimelb.edu.au.
authors.forename: Antanas V
authors.initials: AV
authors.lastname: Spokevicius
authors.affiliation: Victorian AgriBiosciences Centre, La Trobe University R&D Park, 1 Park Drive, Bundoora, Victoria, 3083, Australia.
authors.forename: Josquin
authors.initials: J
authors.lastname: Tibbits
authors.affiliation: GYDLE, 101-1332 Av. Chanoine Morel, Québec, QC, G1S 4B4, Canada.
authors.forename: Philippe
authors.initials: P
authors.lastname: Rigault
authors.affiliation: GYDLE, 101-1332 Av. Chanoine Morel, Québec, QC, G1S 4B4, Canada.
authors.forename: Marc-Alexandre
authors.initials: MA
authors.lastname: Nolin
authors.affiliation: Faculty of Agriculture and the Environment, The University of Sydney, Sydney, 2006, Australia.
authors.forename: Caroline
authors.initials: C
authors.lastname: Müller
authors.affiliation: Faculty of Agriculture and the Environment, The University of Sydney, Sydney, 2006, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Merchant
mesh_terms: D019295:Computational Biology / Q000379:methods; D055864:Droughts; D060146:Ecotype; D005052:Eucalyptus / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D063990:Gene Ontology; D053263:Gene Regulatory Networks; D059014:High-Throughput Nucleotide Sequencing; D053858:Metabolic Networks and Pathways; D058977:Molecular Sequence Annotation; D018515:Plant Leaves; D015398:Signal Transduction; D013312:Stress, Physiological / Q000235:genetics*; D059467:Transcriptome
keywords: Ecotype; Eucalyptus; Homeostasis; Transcriptomic; Water deficit