Abstract
BackgroundEucalyptus, a highly diverse genus of the Myrtaceae family, is the most widely planted hardwood in the world due to its increasing importance for fiber and energy. Somatic embryogenesis (SE) is one large-scale method to provide commercial use of the vegetative propagation of Eucalyptus and dedifferentiation is a key step for plant cells to become meristematic. However, little is known about the molecular changes during the Eucalyptus SE.ResultsWe compared the transcriptome profiles of the differentiated and dedifferentiated tissues of two Eucalyptus species – E. camaldulensis (high embryogenetic potential) and E. grandis x urophylla (low embryogenetic potential). Initially, we identified 18,777 to 20,240 genes in all samples. Compared to the differentiated tissues, we identified 9229 and 8989 differentially expressed genes (DEGs) in the dedifferentiated tissues of E. camaldulensis and E. grandis x urophylla, respectively, and 2687 up-regulated and 2581 down-regulated genes shared. Next, we identified 2003 up-regulated and 1958 down-regulated genes only in E. camaldulensis, including 6 somatic embryogenesis receptor kinase, 17 ethylene, 12 auxin, 83 ribosomal protein, 28 zinc finger protein, 10 heat shock protein, 9 histone, 122 cell wall related and 98 transcription factor genes. Genes from other families like ABA, arabinogalactan protein and late embryogenesis abundant protein were also found to be specifically dysregulated in the dedifferentiation process of E. camaldulensis. Further, we identified 48,447 variants (SNPs and small indels) specific to E. camaldulensis, including 13,434 exonic variants from 4723 genes (e.g., annexin, GN, ARF and AP2-like ethylene-responsive transcription factor). qRT-PCR was used to confirm the gene expression patterns in both E. camaldulensis and E. grandis x urophylla.ConclusionsThis is the first time to study the somatic embryogenesis of Eucalyptus using transcriptome sequencing. It will improve our understanding of the molecular mechanisms of somatic embryogenesis and dedifferentiation in Eucalyptus. Our results provide a valuable resource for future studies in the field of Eucalyptus and will benefit the Eucalyptus breeding program.
Highlights
Eucalyptus, a highly diverse genus of the Myrtaceae family, is the most widely planted hardwood in the world due to its increasing importance for fiber and energy
Morphological characterization of somatic callus To study the somatic embryogenesis of Eucalyptus, the stem segments of both E. camaldulensis (A1) and E. grandis x urophylla (A2) were tissue-culture induced to callus (B1 for E. camaldulensis and B2 for E. grandis x urophylla)
In conclusion, we studied the transcriptome profiles during the Somatic embryogenesis (SE) of two Eucalyptus species – E. camaldulensis and E. grandis x urophylla
Summary
Eucalyptus, a highly diverse genus of the Myrtaceae family, is the most widely planted hardwood in the world due to its increasing importance for fiber and energy. Somatic embryogenesis (SE) is one large-scale method to provide commercial use of the vegetative propagation of Eucalyptus and dedifferentiation is a key step for plant cells to become meristematic. Eucalyptus is a highly diverse genus of the Myrtaceae family and is widely planted across the world for its increasing importance for timber and pulp [1]. Some tissues (e.g., hypocotyls, cotyledons, leaves, shoots) from both young seedlings and old trees have been reported for successful induction of callus in multiple Eucalyptus species, such as E. botryoides, E. dunnii, E. grandis, E. globulus and E. rudis [5]. It is clear that the capacity of SE in Eucalyptus species varies, our knowledge about the genomic and transcriptomic information controlling the SE and vegetative propagation is still poor
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