Abstract
Apple trees require a long exposure to chilling temperature during winter to acquire competency to flower and grow in the following spring. Climate change or adverse meteorological conditions can impair release of dormancy and delay bud break, hence jeopardizing fruit production and causing substantial economic losses. In order to characterize the molecular mechanisms controlling bud dormancy in apple we focused our work on the MADS-box transcription factor gene MdDAM1. We show that MdDAM1 silencing is required for the release of dormancy and bud break in spring. MdDAM1 transcript levels are drastically reduced in the low-chill varieties ‘Anna’ and ‘Dorsett Golden’ compared to ‘Golden Delicious’ corroborating its role as a key genetic factor controlling the release of bud dormancy in Malus species. The functional characterization of MdDAM1 using RNA silencing resulted in trees unable to cease growth in winter and that displayed an evergrowing, or evergreen, phenotype several years after transgenesis. These trees lost their capacity to enter in dormancy and produced leaves and shoots regardless of the season. A transcriptome study revealed that apple evergrowing lines are a genocopy of ‘Golden Delicious’ trees at the onset of the bud break with the significant gene repression of the related MADS-box gene MdDAM4 as a major feature. We provide the first functional evidence that MADS-box transcriptional factors are key regulators of bud dormancy in pome fruit trees and demonstrate that their silencing results in a defect of growth cessation in autumn. Our findings will help producing low-chill apple variants from the elite commercial cultivars that will withstand climate change.
Highlights
Apple (Malus × domestica Borkh.) is an economically important fruit tree cultivated in temperate regions around the globe
MdDAM1 was expressed at high levels in dormant buds of ‘Golden Delicious’ collected in October and November and was gradually repressed during dormancy in winter to be completely silenced in March when the bud breaks and the temperature as well as the day length increase at the onset of spring (Figure 1, Figure S1)
Our results clearly indicate that silencing of MdDAM1 in apple trees leads to a loss of bud dormancy an abolishment of growth cessation that usually occurs in autumn
Summary
Apple (Malus × domestica Borkh.) is an economically important fruit tree cultivated in temperate regions around the globe. When grown in the Northern Hemisphere, apple trees usually enter in dormancy at the beginning of autumn. Fruitlets are rapidly formed in spring and fruits grow and ripen during summer During this period, terminal and lateral buds are formed and will gradually enter in dormancy. Buds are considered endodormant when a signal within the bud triggers deep dormancy that occurs typically during autumn and winter At this stage, development is suppressed even in growth conducive conditions. After endodormancy has been completed the plant still remains dormant This period is called ecodormancy since buds are usually exposed to harsh environmental conditions unfavorable for growth, such as temperatures below 10°C (Lang, 1987). Once the ambient temperature increases, the bud breaks quickly, followed by a rapid growth of leaf and flower structures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
