Adventitious rooting is an essential biological process in the vegetative propagation of economically important horticultural and forest tree species. It enables utilization of the elite genotypes in breeding programmes and production. Promotion of adventitious root (AR) formation has been associated with starvation of inorganic phosphate and some factors involved in low phosphorus (LP) signalling. However, the regulatory mechanism underlying LP-mediated AR formation remains largely elusive. We established an efficient experimental system that guaranteed AR formation through short-term LP treatment in Populus ussuriensis. We then generated a time-course RNA-seq data set to recognize key regulatory genes and regulatory cascades positively regulating AR formation through data analysis and gene network construction, which were followed by experimental validation and characterization. We constructed a multilayered hierarchical gene regulatory network, from which PuMYB40, a typical R2R3-type MYB transcription factor (TF), and its interactive partner, PuWRKY75, as well as their direct targets, PuLRP1 and PuERF003, were identified to function upstream of the known adventitious rooting genes. These regulatory genes were functionally characterized and proved their roles in promoting AR formation in P. ussuriensis. In conclusion, our study unveiled a new hierarchical regulatory network that promoted AR formation in P. ussuriensis, which was activated by short-term LP stimulus and primarily governed by PuMYB40 and PuWRKY75.

中文翻译：

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两个高级调控因子 PuMYB40 和 PuWRKY75 控制乌苏里杨中低磷驱动的不定根形成

不定生根是经济上重要的园艺和森林树种无性繁殖的重要生物学过程。它能够在育种计划和生产中利用优良基因型。促进不定根 (AR) 的形成与无机磷酸盐的缺乏和一些参与低磷 (LP) 信号传导的因素有关。然而，LP 介导的 AR 形成的调控机制在很大程度上仍然难以捉摸。我们建立了一个有效的实验系统，通过对乌苏里杨的短期 LP 处理来保证 AR 的形成. 然后，我们生成了一个时程 RNA-seq 数据集，通过数据分析和基因网络构建，识别关键调控基因和调控级联反应正调控 AR 的形成，然后进行实验验证和表征。我们构建了一个多层次的基因调控网络，从中鉴定出典型的 R2R3 型 MYB 转录因子 (TF) PuMYB40 及其相互作用的伙伴 PuWRKY75 以及它们的直接靶标PuLRP1和PuERF003在已知的不定生根基因。这些调节基因在功能上进行了表征，并证明了它们在促进乌苏里杨的 AR 形成中的作用. 总之，我们的研究揭示了一个新的分层监管网络，促进了乌苏里白杨中 AR 的形成，该网络由短期 LP 刺激激活，主要由 PuMYB40 和 PuWRKY75 控制。