Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
Key Laboratory of Horticultural Plant Biology of Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, China.
New Phytol. 2017 Jul;215(2):642-657. doi: 10.1111/nph.14631. Epub 2017 Jun 13.
Plant secondary growth derives from the meristematic activity of the vascular cambium. In Arabidopsis thaliana, cell divisions in the cambium are regulated by the transcription factor WOX4, a key target of the CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION (ESR)-RELATED 41 (CLE41) signaling pathway. However, function of the WOX4-like genes in plants that are dependent on a much more prolific secondary growth, such as trees, remains unclear. Here, we investigate the role of WOX4 and CLE41 homologs for stem secondary growth in Populus trees. In Populus, PttWOX4 genes are specifically expressed in the cambial region during vegetative growth, but not after growth cessation and during dormancy, possibly involving a regulation by auxin. In PttWOX4a/b RNAi trees, primary growth was not affected whereas the width of the vascular cambium was severely reduced and secondary growth was greatly diminished. Our data show that in Populus trees, PttWOX4 genes control cell division activity in the vascular cambium, and hence growth in stem girth. This activity involves the positive regulation of PttWOX4a/b through PttCLE41-related genes. Finally, expression profiling suggests that the CLE41 signaling pathway is an evolutionarily conserved program for the regulation of vascular cambium activity between angiosperm and gymnosperm tree species.
植物次生生长源于维管形成层的分生组织活动。在拟南芥中，形成层的细胞分裂受转录因子 WOX4 的调控，WOX4 是 CLAVATA3（CLV3）/胚胎周围区域（ESR）相关 41（CLE41）信号通路的关键靶标。然而，WOX4 样基因在依赖于更丰富次生生长的植物（如树木）中的功能仍不清楚。在这里，我们研究了 WOX4 和 CLE41 同源物在杨树茎次生生长中的作用。在杨树中，PttWOX4 基因在营养生长期间特异性地在形成层区域表达，但在生长停止和休眠期间不表达，可能涉及生长素的调节。在 PttWOX4a/b RNAi 树木中，初级生长不受影响，而维管形成层的宽度严重减小，次生生长大大减少。我们的数据表明，在杨树中，PttWOX4 基因控制维管形成层的细胞分裂活动，从而控制茎周长的生长。这种活性通过 PttCLE41 相关基因对 PttWOX4a/b 的正调控来实现。最后，表达谱分析表明，CLE41 信号通路是调控被子植物和裸子植物树种维管形成层活性的一个进化保守的程序。
