Plant breeders have focused much attention on polyploid trees because of their importance to forestry. To evaluate the impact of intraspecies genome duplication on the transcriptome, a series of Betula platyphylla autotetraploids and diploids were generated from four full-sib families. The phenotypes and transcriptomes of these autotetraploid individuals were compared with those of diploid trees. Autotetraploids were generally superior in breast-height diameter, volume, leaf, fruit and stoma and were generally inferior in height compared to diploids. Transcriptome data revealed numerous changes in gene expression attributable to autotetraploidization, which resulted in the upregulation of 7052 unigenes and the downregulation of 3658 unigenes. Pathway analysis revealed that the biosynthesis and signal transduction of indoleacetate (IAA) and ethylene were altered after genome duplication, which may have contributed to phenotypic changes. These results shed light on variations in birch autotetraploidization and help identify important genes for the genetic engineering of birch trees.

Integration of T-DNA into plant genomes via Agrobacterium may interrupt gene structure and generate numerous mutants. The T-DNA caused mutants are valuable materials for understanding T-DNA integration model in plant research. T-DNA integration in plants is complex and still largely unknown. In this work, we reported that multiple T-DNA fragments caused chromosomal translocation and deletion in a birch (Betula platyphylla × B. pendula) T-DNA mutant yl. We performed PacBio genome resequencing for yl and the result revealed that two ends of a T-DNA can be integrated into plant genome independently because the two ends can be linked to different chromosomes and cause chromosomal translocation. We also found that these T-DNA were connected into tandem fragment regardless of direction before integrating into plant genome. In addition, the integration of T-DNA in yl genome also caused several chromosomal fragments deletion. We then summarized three cases for T-DNA integration model in the yl genome. (1) A T-DNA fragment is linked to the two ends of a double-stranded break (DSB); (2) Only one end of a T-DNA fragment is linked to a DSB; (3) A T-DNA fragment is linked to the ends of different DSBs. All the observations in the yl genome supported the DSB repair model. In this study, we showed a comprehensive genome analysis of a T-DNA mutant and provide a new insight into T-DNA integration in plants. These findings would be helpful for the analysis of T-DNA mutants with special phenotypes.