Chongqing Key Laboratory of Plant Resource Conservation and Germplasm Innovation, School of Life Sciences, Southwest University, Chongqing, 400715, China.
Key Laboratory of Eco-environments of Three Gorges Reservoir Region, Ministry of Education, School of Life Sciences, Southwest University, Chongqing, 400715, China.
New Phytol. 2021 May;230(4):1476-1488. doi: 10.1111/nph.17255. Epub 2021 Mar 8.
The regulation of cytokinin on secondary vascular development has been uncovered by modulating cytokinin content. However, it remains unclear how cytokinin enriched in developing secondary phloem regulates cambium activity in poplar. Here, we visualized the gradient distribution of cytokinin with a peak in the secondary phloem of poplar stem via immunohistochemical imaging, and determined the role of phloem-located cytokinin signaling during wood formation. We generated transgenic poplar harboring cytokinin oxidase/dehydrogenase (CKX)2, a gene encoding a cytokinin degrading enzyme, driven by the phloem-specific CLE41b promoter, indicating that the disruption of the cytokinin gradient pattern restricts the cambial activity. The RNA interference-based knockdown of the histidine kinase (HK) genes encoding cytokinin receptors specifically in secondary phloem significantly compromised the division activity of cambial cells, whereas the phloem-specific expression of a type-B response regulator (RR) transcription factor stimulated cambial proliferation, providing evidence for the noncell-autonomous regulation of local cytokinin signaling on the cambial activity. Moreover, the cambium-specific knockdown of HKs also led to restricted cambial activity, and the defects were aggravated by the reduced cytokinin accumulation. Our results showed that local cytokinin signaling in secondary phloem regulates cambial activity noncell-autonomously, and coordinately with its local signaling in cambium.
通过调节细胞分裂素的含量，揭示了细胞分裂素对次生维管发育的调节作用。然而，细胞分裂素在发育中的次生韧皮部中富集如何调节杨树形成层的活性仍不清楚。在这里，我们通过免疫组织化学成像，可视化了杨树茎次生韧皮部中细胞分裂素的梯度分布，其峰值出现在次生韧皮部中，并确定了木质部定位的细胞分裂素信号在木材形成过程中的作用。我们通过 phloem-specific CLE41b 启动子驱动的细胞分裂素氧化酶/脱氢酶（CKX）2 基因（编码细胞分裂素降解酶）的转化，产生了含有细胞分裂素梯度模式的杨树，表明破坏细胞分裂素梯度模式限制了形成层的活性。HK 基因（编码细胞分裂素受体）的 RNAi 敲低特异性在次生韧皮部中，明显削弱了形成层细胞的分裂活性，而 RR 转录因子（编码细胞分裂素受体）的 phloem-specific 表达则刺激了形成层的增殖，为局部细胞分裂素信号对形成层活性的非细胞自主调控提供了证据。此外，HKs 的形成层特异性敲低也导致了形成层活性的限制，并且细胞分裂素积累减少加剧了缺陷。我们的结果表明，次生韧皮部中的局部细胞分裂素信号非自主地调节形成层的活性，并与局部的信号协调作用。
