Functional Characterization of Japanese Apricot (Prunus mume) DORMANCYASSOCIATED MADS-box1 (PmDAM1), a Paralog of PmDAM6, Using Populus Transformants

Abstract

In Japanese apricot (Prunus mume), six MADS-box genes called DORMANCY-ASSOCIATED MADS-box (PmDAM1-6) are present in a tandem arrangement and are expressed in leaves and buds during the dormant season. Among them, PmDAM1 is up-regulated during the summer when shoot growth is terminated, and it is down-regulated long before dormancy release. To investigate the biological function of PmDAM1, we performed transgenic studies using hybrid poplar (Populus tremula × tremuloides; clone T89). The growth rate of poplar transformed with 35S:PmDAM1 was the same as that of wild-type (WT) poplars. However, 35S:PmDAM1 poplars formed terminal buds earlier than the WT, although terminal buds started to regrow in some 35S:PmDAM1 poplars soon after terminal bud formation. Following artificial cold exposures, the resumption of bud outgrowth in 35S:PmDAM1 poplars was relatively slow compared with the WT when the plants were grown in semi-field conditions that forced bud outgrowth. These results suggested that PmDAM1 caused growth inhibitory effects in transgenic poplar during the transition from growth to growth cessation and from dormancy release to bud outgrowth, when there were limited growth-promoting factors. Based on the data obtained from this poplar transformation study and the seasonal expression pattern of PmDAM1 in Japanese apricot, the involvement of PmDAM1 in the dormancy regulation of Japanese apricot is discussed.