Abstract:
NAC domain transcription factors regulate many developmental processes and stress
responses in plants and vary widely in number and family structure. We analysed the
characteristics and evolution of the NAC gene family of Eucalyptus grandis, a fastgrowing
forest tree in the rosid order Myrtales. NAC domain genes identified in the E. grandis genome were subjected to amino acid
sequence, phylogenetic and motif analyses. Transcript abundance in developing tissues
and abiotic stress conditions in E. grandis and E. globulus was quantified using RNA-seq
and RT-qPCR.189 E. grandis NAC (EgrNAC) proteins, arranged into 22 subfamilies, are extensively
duplicated in subfamilies associated with stress response. Most EgrNAC genes form
tandem duplicate arrays that frequently carry signatures of purifying selection. Sixteen
amino acid motifs were identified in EgrNAC proteins, eight of which are enriched in, or
unique to, Eucalyptus. New candidates for the regulation of normal and tension wood
development and cold responses were identified.This first description of a Myrtales NAC domain family reveals a unique history of
tandem duplication in stress-related subfamilies that has likely contributed to the
adaptation of eucalypts to the challenging Australian environment. Several new
candidates for the regulation of stress, wood formation and tree-specific development are
reported.
