Cytokinin signaling regulates cambial development in poplar
Cytokinin signaling regulates cambial development in poplar
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DOI：
10.1073/pnas.0805617106
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发表时间：
2008-12-16
影响因子：
11.1
通讯作者：
Helariutta, Yka
中科院分区：
文献类型：
--
作者：
Nieminen, Kaisa;Immanen, Juha;Helariutta, Yka
虽然植物生物量的很大一部分来源于维管形成层的活动，但植物径向生长的分子基础仍然是未知的。为了解决是否需要细胞分裂素的形成层活动，我们研究了细胞分裂素信号跨越形成层区的2个树种，白杨（杨）和桦树（白桦）。我们观察到的基因编码细胞分裂素受体在分裂形成层细胞的表达高峰。我们通过改造转基因白杨（P. tremula x tremuloides），在桦树细胞分裂素受体1基因的启动子下表达细胞分裂素分解代谢基因拟南芥细胞分裂素氧化酶2，从而内源性降低细胞分裂素水平。转基因树显示生物活性细胞分裂素的浓度降低，与受损的细胞分裂素反应。在这些树木中，顶端和径向生长受到损害。然而，径向生长的影响更大，如所示的一个更薄的茎直径比野生型在相同的高度。为了区分径向和顶端生长抑制，我们进行了相互嫁接实验。野生型接穗生长超过转基因股票的直径，暗示细胞分裂素活性作为径向生长的直接决定因素。减少径向生长与形成层细胞层数减少。此外，在细茎转基因树中，细胞分裂素初级反应基因的表达显著降低。因此，细胞分裂素信号传导水平的降低是观察到的形成层生长受损的主要基础。总之，我们的研究结果表明，细胞分裂素是形成层发育所需的主要激素调节剂。
Although a substantial proportion of plant biomass originates from the activity of vascular cambium, the molecular basis of radial plant growth is still largely unknown. To address whether cytokinins are required for cambial activity, we studied cytokinin signaling across the cambial zones of 2 tree species, poplar (Populus trichocarpa) and birch (Betula pendula). We observed an expression peak for genes encoding cytokinin receptors in the dividing cambial cells. We reduced cytokinin levels endogenously by engineering transgenic poplar trees (P. tremula x tremuloides) to express a cytokinin catabolic gene, Arabidopsis CYTOKININ OXIDASE 2, under the promoter of a birch CYTOKININ RECEPTOR 1 gene. Transgenic trees showed reduced concentration of a biologically active cytokinin, correlating with impaired cytokinin responsiveness. In these trees, both apical and radial growth was compromised. However, radial growth was more affected, as illustrated by a thinner stem diameter than in WT at same height. To dissect radial from apical growth inhibition, we performed a reciprocal grafting experiment. WT scion outgrew the diameter of transgenic stock, implicating cytokinin activity as a direct determinant of radial growth. The reduced radial growth correlated with a reduced number of cambial cell layers. Moreover, expression of a cytokinin primary response gene was dramatically reduced in the thin-stemmed transgenic trees. Thus, a reduced level of cytokinin signaling is the primary basis for the impaired cambial growth observed. Together, our results show that cytokinins are major hormonal regulators required for cambial development.