Expression analysis of apple DORMANCY-ASSOCIATED MADS-box genes in ‘Fuji’ dormant flower buds during flower bud development

Abstract

Most temperate fruit tree species enter dormancy in autumn and come out of dormancy after exposure to a certain amount of chilling. Recent global climate change affects bud dormancy of temperate fruit trees in Japan and might interfere with bud dormancy and blooming dates in apple trees (Malus × domestica) in the future. However, our knowledge of molecular mechanisms underlying endodormancy release and the genetic factors controlling chilling requirements and blooming date in apple is limited. In peach (Prunus persica) and P. mume (Rosaceae), DORMANCY-ASSOCIATED MADS-box (DAM) genes have been identified as candidate key factors controlling chilling requirements. We previously analysed gene expressions of two apple DAM-like genes, MdDAM1 (MD322567) and MdDAM2 (MD259294), in dormant buds collected from apple trees grown in Kyoto, Japan, and reported that MdDAM2 was constantly downregulated during dormancy release in the same manner as Prunus DAMs. In this study, we performed seasonal expression analysis of two apple DAM-like genes in ‘Fuji’ flower buds collected from trees grown in Nagano, Japan, with special attention to the morphological changes of internal flower structure. The analysis revealed that both genes were upregulated during the flowering initiation stage, from June to Aug. After inflorescence development, MdDAM2 was constantly downregulated during the flower organ differentiation stage, while MdDAM1 was expressed at a relatively higher level throughout the flower organ differentiation stage. Based on these results the relationship between flower organ development and the expressions of DAMs in fruit tree species of Rosaceae is discussed.