Li Xu, Shen Fei, Xu Xiaozhao, Zheng Qingbo, Wang Yi, Wu Ting, Li Wei, Qiu Changpeng, Xu Xuefeng, Han Zhenhai, Zhang Xinzhong
College of Horticulture, China Agricultural University, Beijing, China.
Plant J. 2021 Sep;107(6):1663-1680. doi: 10.1111/tpj.15406. Epub 2021 Jul 28.
Adventitious root (AR) formation is a critical factor in the vegetative propagation of forestry and horticultural plants. Competence for AR formation declines in many species during the miR156/SPL-mediated vegetative phase change. Auxin also plays a regulatory role in AR formation. In apple rootstock, both high miR156 expression and exogenous auxin application are prerequisites for AR formation. However, the mechanism by which the miR156/SPL module interacts with auxin in controlling AR formation is unclear. In this paper, leafy cuttings of juvenile (Mx-J) and adult (Mx-A) phase Malus xiaojinensis were used in an RNA-sequencing experiment. The results revealed that numerous genes involved in phytohormone signaling, carbohydrate metabolism, cell dedifferentiation, and reactivation were downregulated in Mx-A cuttings in response to indole butyric acid treatment. Among the differentially expressed genes, an HD-ZIP transcription factor gene, MxHB13, was found to be under negative regulation of MdSPL26 by directly binding to MxHB13 promoter. MxTIFY9 interacts with MxSPL26 and may play a role in co-repressing the expression of MxHB13. The expression of MxTIFY9 was induced by exogenous indole butyric acid. MxHB13 binds to the promoter of MxABCB19-2 and positively affects the expression. A model is proposed in which MxHB13 links juvenility-limited and auxin-limited AR recalcitrance mechanisms in Mx-A.
不定根（AR）形成是林业和园艺植物营养繁殖中的一个关键因素。在miR156/SPL介导的营养阶段转变过程中，许多物种形成不定根的能力会下降。生长素在不定根形成中也发挥着调节作用。在苹果砧木中，高miR156表达和外源生长素处理都是不定根形成的先决条件。然而，miR156/SPL模块与生长素在控制不定根形成过程中相互作用的机制尚不清楚。本文利用小金海棠幼年（Mx-J）和成年（Mx-A）阶段的带叶插条进行了RNA测序实验。结果表明，在Mx-A插条中，许多参与植物激素信号传导、碳水化合物代谢、细胞去分化和再激活的基因在吲哚丁酸处理下表达下调。在差异表达基因中，发现一个HD-ZIP转录因子基因MxHB13受到MdSPL26 的负调控，MdSPL26通过直接结合MxHB13启动子来实现这种调控。MxTIFY9与MxSPL26相互作用，可能在共同抑制MxHB13的表达中发挥作用。MxTIFY9的表达受外源吲哚丁酸诱导。MxHB13与MxABCB19-2的启动子结合，并对其表达产生正向影响。本文提出了一个模型，其中MxHB13在Mx-A中连接了幼年限制和生长素限制的不定根难形成机制。
