Dynamics of phytohormone and DNA methylation patterns changes during dormancy induction in strawberry (Fragaria x ananassa Duch.)

Changes in endogenous phytohormone levels, DNA methylation patterns, and expression levels of related genes during induction of dormancy in two strawberry cultivars, Darselect and All Star, were studied under controlled environmental conditions. At 12 degrees C, regardless of day length, potted, runner-derived plants of both cultivars gradually exhibited morphological traits typical of dormancy after treatment for 8 weeks. These morphological changes were accompanied by a synchronous significant decline in indole-3-acetic acid (IAA) level and increases in abscisic acid (ABA) content and global genomic DNA methylation in young leaves. Exposed at 15 degrees C and a short-day photoperiod, the changes in morphology, phytohormone levels and DNA methylation of both cultivars were similar to those observed at 12 degrees C. Slight but non-significant changes in IAA and ABA levels and genomic DNA methylation occurred in young leaves at both 15 degrees C with long days and 18 degrees C with short days. These results indicated that temperature alone was sufficient to induce strawberry to enter the typical dormant phase, and day length had no impact at 12 degrees C. The higher temperature permissible for dormancy induction in strawberry was 15 degrees C, but at this temperature dormancy induction was modified by day length. The expression patterns of FaPIN1, FaNCED1, FaDRM and FaROS1 were coincident with the changes in phytohormone levels and DNA methylation. Although the two tested cultivars have different temporal responses with the different degree of cold tolerance and depth of dormancy, both the endogenous phytohormone and DNA methylation were changed when induced by external environmental factors.