Histone modification and signalling cascade of the dormancy-associatedMADS-box gene, PpMADS13-1, in Japanese pear (Pyrus pyrifolia) during endodormancy

Dormancy-associatedMADS-box (DAM) genes play an important role in endodormancy phase transition. We investigated histone modification in the DAM homolog (PpMADS13-1) from Japanese pear, via chromatin immunoprecipitation-quantitative PCR, to understand the mechanism behind the reduced expression of the PpMADS13-1 gene towards endodormancy release. Our results indicated that the reduction in the active histone mark by trimethylation of the histone H3 tail at lysine 4 contributed to the reduction of PpMADS13-1 expression towards endodormancy release. In contrast, the inactive histone mark by trimethylation of the histone H3 tail at lysine 27 in PpMADS13-1 locus was quite low, and these levels were more similar to a negative control [normal mouse immunoglobulin G (IgG)] than to a positive control (AGAMOUS) in endodormancy phase transition. The loss of histone variant H2A.Z also coincided with the down-regulation of PpMADS13-1. Subsequently, we investigated the PpMADS13-1 signalling cascade and found that PpCBF2, a pear C-repeated binding factor, regulated PpMADS13-1 expression via interaction of PpCBF2 with the 5'-upstream region of PpMADS13-1 by transient reporter assay. Furthermore, transient reporter assay confirmed no interaction between the PpMADS13-1 protein and the pear FLOWERING LOCUS T genes. Taken together, our results enhance understanding of the molecular mechanisms underlying endodormancy phase transition in Japanese pear. Under global warming, dysfunction of normal dormancy phase transition is observed in Japanese pear cultivation. Therefore, elucidation of mechanisms underlying physiological changes associated with dormancy phase transition is required. We found that reduction in the active histone mark by trimethylation of the histone H3 tail at lysine 4 and histone variant H2A.Z contributed to the reduction of DAM homolog (PpMADS13 -1) expression toward endodormancy release in Japanese pear. We also indicated that PpCBF2 regulated PpMADS13 -1 expression via interaction of PpCBF2 with the 5'-upstream region of PpMADS13 -1 by transient reporter assay. Furthermore, transient reporter assay confirmed no interaction between the PpMADS13-1 protein and the pear FLOWERING LOCUS T genes.