Abstract
The CBF signal pathway is responsible for a significant portion of plant responses to low temperature and freezing. Overexpression of CBF genes in model organisms such as Arabidopsis thaliana enhances abiotic stress tolerance but also reduces growth. In addition to these effects, overexpression of the peach (Prunus persica [L.] Batsch) CBF1 gene in transgenic apple (Malus x domestica Borkh.) line T166 also results in early entry into and late exit from dormancy. Although the regulation of dormancy-induction and dormancy-release occur while the CBF regulon is operative in perennial, woody plants, how overexpression of CBF1 affects these dormancy-related changes in gene expression is incompletely understood. The objective of the present study was to characterize global changes in gene expression in peach CBF1-overexpressing and non-transformed apple bark tissues at different states of dormancy via RNA-seq. RNA-seq bioinformatics data was confirmed by RT-qPCR on a number of genes. Results indicate that the greatest number of significantly differentially expressed genes (DEGs) occurred in April when dormancy release and bud break normally occur but are delayed in Line T166. Genes involved in storage and inactivation of auxin, GA, and cytokinin were generally upregulated in T166 in April, while those for biosynthesis, uptake or signal transduction were generally downregulated in T166. Genes for cell division and cambial growth were also downregulated in T166 relative to the non-transformed line. These data suggest that overexpression of the peach CBF1 gene impacts growth hormone homeostasis and as a result the activation of growth in the spring, and most likely growth cessation in the fall as well.
Highlights
The domesticated apple, Malus × domestica Borkh., is a member of the family Rosaceae, tribe Pyreae, and is grown world-wide
An average of 89% of the clean reads were successfully aligned to the apple reference genome[21], and an average of 31,483 genes or protein coding transcripts were identified between both genotypes and over all timepoints
Overall analysis of differentially upregulated and downregulated genes based on the experimental variables: (1) comparisons between the genotypes at each of the sampled months; (2) genes that were differentially expressed over time within a genotype; (3) genes that were differentially expressed in one sampling point to the sampling point, and; (4) genes that were differentially expressed based on
Summary
The domesticated apple, Malus × domestica Borkh., is a member of the family Rosaceae, tribe Pyreae, and is grown world-wide. Over 100 varieties are grown commercially in the United States, with an annual average of 240 million bushels of apples worth close to $4 billion (wholesale). Global production of apples for 2016/2017 exceeded 77 million metric tons Data from the USDA Risk Management Agency for the years 2007–2017 indicates that apple growers claimed $157,177,390 in insured losses from freeze damage (https:// www.rma.usda.gov/informationtools/). The majority of this damage occurred in the spring, when abnormally warm temperatures were followed by freezing temperatures[1].
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