Ruonala Raili, Rinne Päivi L H, Kangasjärvi Jaakko, van der Schoot Christiaan
Plant Biology, Department of Biological and Environmental Sciences, University of Helsinki, FI-00014 Helsinki, Finland.
Plant Cell. 2008 Jan;20(1):59-74. doi: 10.1105/tpc.107.056721. Epub 2008 Jan 11.
We investigated the short day (SD)-induced transition to dormancy in wild-type hybrid poplar (Populus tremula x P. tremuloides) and its absence in transgenic poplar overexpressing heterologous PHYTOCHROME A (PHYA). CENTRORADIALIS-LIKE1 (CENL1), a poplar ortholog of Arabidopsis thaliana TERMINAL FLOWER1 (TFL1), was markedly downregulated in the wild-type apex coincident with SD-induced growth cessation. By contrast, poplar overexpressing a heterologous Avena sativa PHYA construct (P35S:AsPHYA), with PHYA accumulating in the rib meristem (RM) and adjacent tissues but not in the shoot apical meristem (SAM), upregulated CENL1 in the RM area coincident with an acceleration of stem elongation. In SD-exposed heterografts, both P35S:AsPHYA and wild-type scions ceased growth and formed buds, whereas only the wild type assumed dormancy and P35S:AsPHYA showed repetitive flushing. This shows that the transition is not dictated by leaf-produced signals but dependent on RM and SAM properties. In view of this, callose-enforced cell isolation in the SAM, associated with suspension of indeterminate growth during dormancy, may require downregulation of CENL1 in the RM. Accordingly, upregulation of CENL1/TFL1 might promote stem elongation in poplar as well as in Arabidopsis during bolting. Together, the results suggest that the RM is particularly sensitive to photoperiodic signals and that CENL1 in the RM influences transition to dormancy in hybrid poplar.
我们研究了短日照（SD）诱导野生型杂交杨树（Populus tremula x P. tremuloides）进入休眠的过程，以及过量表达异源光敏色素A（PHYA）的转基因杨树不存在这种休眠转变的情况。CENTRORADIALIS-LIKE1（CENL1）是拟南芥TERMINAL FLOWER1（TFL1）的杨树直系同源基因，在野生型杨树顶端与SD诱导的生长停止同时显著下调。相比之下，过量表达异源燕麦PHYA构建体（P35S:AsPHYA）的杨树，其PHYA在肋分生组织（RM）和相邻组织中积累，但不在茎尖分生组织（SAM）中积累，在RM区域CENL1上调，同时茎伸长加速。在暴露于SD的异种嫁接中，P35S:AsPHYA和野生型接穗都停止生长并形成芽，但只有野生型进入休眠，而P35S:AsPHYA表现出反复抽梢。这表明这种转变不是由叶片产生的信号决定的，而是取决于RM和SAM的特性。鉴于此，SAM中胼胝质介导的细胞隔离与休眠期间无限生长的暂停相关，可能需要RM中CENL1的下调。因此，CENL1/TFL1的上调可能在杨树以及拟南芥抽薹期间促进茎的伸长。总之，结果表明RM对光周期信号特别敏感，并且RM中的CENL1影响杂交杨树向休眠的转变。
