Differential gene expression in nontransgenic and transgenic "M.26" apple overexpressing a peach CBF gene during the transition from eco-dormancy to bud break

Authors: Artlip, Timothy - Tim; MCDERMAID, ADAM - South Dakota State University; MA, QING - South Dakota State University; Wisniewski, Michael

Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2019
Publication Date: 7/11/2019
Citation: Artlip, T.S., Mcdermaid, A., Ma, Q., Wisniewski, M.E. 2019. Differential gene expression in nontransgenic and transgenic "M.26" apple overexpressing a peach CBF gene during the transition from eco-dormancy to bud break. Horticulture Research. https://doi.org/10.1038/s41438-019-0168-9.
DOI: https://doi.org/10.1038/s41438-019-0168-9

Interpretive Summary: Due to erratic spring weather events, many types of fruit crops undergo budbreak and flowering earlier and earlier in the spring. Then, they are subsequently injured or killed when more seasonable, freezing weather returns. Billions of dollars of lost profit to fruit growers and higher prices to consumers have resulted from several spring frost events over the past few years. Therefore, it is imperative to develop fruit cultivars with improved hardiness and/or delayed dormancy. Previous USDA-ARS research demonstrated that a transgenic apple rootstock (T166) overexpressing a C-repeat Binding Factor (CBF) gene had increased levels of freezing tolerance, delayed spring budbreak, and reduced growth. Understanding the mechanisms by which these altered traits occur is important to introducing them into commercial apple varieties. The global expression of genes in transgenic T166 versus the non-transformed parent, M.26, from early spring to mid-summer was conducted using RNAseq. It appears that overexpressing a CBF gene appears to directly and indirectly affect plant hormone signaling pathways and probably hormone levels as well. These effects are most pronounced during April, coinciding with delayed budbreak in T166. It may be possible to breed for specific changes in plant hormone targets resulting in delayed budbreak and enhanced tolerance to erratic weather patterns.

Technical Abstract: The C-repeat Binding Factor (CBF) transcription factor is involved in responses to low temperature and water deficit in many plant species. Overexpression of CBF genes leads to enhanced freezing tolerance and growth inhibition in many species. The overexpression of a peach CBF (PpCBF1) gene in transgenic line of own-rooted apple (Malus x domestica) M.26 rootstock (T166) trees was previously reported to have additional effects on the onset of dormancy and time of spring budbreak. The goal of the present study was to characterize global changes in gene expression in peach CBF1-overexpressing and non-transformed apple bark tissues over time via RNA-seq. The RNA-seq bioinformatics model was verified on a limited number of genes using RT-qPCR. It was found that the greatest number of highly differentially expressed genes occurred in April, when dormancy release and bud break normally occur but are delayed in Line T166. Genes for auxin, GA and cytokinin storage, and inactivation were generally upregulated in T166 in April. While those for biosynthesis, uptake or signal transduction were generally downregulated in T166. Concomitantly, genes for cell division and cambial growth were also down regulated in T166 compared to the non-transformed line. These data suggest that overexpression of the peach CBF1 gene directly and indirectly impacts growth hormone homeostasis and growth as a result.