背景回顾：Adventitious root (AR) formation plays an important role in vegetatively propagated plants. 

提出问题：Cytokinin (CK) inhibits AR formation, but the molecular mechanisms driving this process remain unknown. 

结果1-CK与AR形成：In this study, we confirmed that CK content is related to AR formation and further revealed that a high auxin/CK ratio was beneficial to AR formation in apple (Malus domestica). 

结果2-TCP17抑制AR形成：A correlation between expression of CK-responsive TEOSINTE BRANCHED1, CYCLOIDEA, and PCF17 (MdTCP17) and AR formation in response to CK was identified, and overexpression of MdTCP17 in transgenic apple inhibited AR formation. 

结果3-TCP17与WOX11互作：Yeast two-hybrid, bimolecular fluorescence complementation, and co-immunoprecipitation assays revealed an interaction between MdTCP17 and WUSCHEL-RELATED HOMEOBOX11 (MdWOX11), and a significant correlation between the expression of MdWOX11 and AR ability. 

结果4-WOX11促进AR形成：Overexpression of MdWOX11 promoted AR primordium formation in apple, while interference of MdWOX11 inhibited AR primordium production. 

结果5-WOX11促进LBD29表达：Moreover, a positive correlation was found between MdWOX11 and LATERAL ORGAN BOUNDARIES DOMAIN29 (MdLBD29) expression, and yeast one-hybrid, dual luciferase reporter, and ChIP-qPCR assays verified the binding of MdWOX11 to the MdLBD29 promoter with a WOX-box element in the binding sequence. 

结果6-TCP7抑制WOX11介导的LBD29促进：Furthermore, MdTCP17 reduced the binding of MdWOX11 and MdLBD29 promoters, and co-expression of MdTCP17 and MdWOX11 reduced MdLBD29 expression. 

结论：Together, these results explain the function and molecular mechanism of MdTCP17-mediated CK inhibition of AR primordium formation, which could be used to improve apple rootstocks genetically.

不定根形成在植物的营养繁殖中发挥着重要作用。细胞分裂素抑制不定根形成，但是具体的分子机制并不清晰。本文中，作者发现在苹果中细胞分裂素含量与不定根的形成相关，并且一个高的生长素/细胞分裂素比例有助于不定根的形成。作者发现细胞分裂素响应基因MdTCP17的表达与响应于细胞分裂素的不定根形成存在关联，过表达MdTCP17的苹果植株的不定根形成受到了抑制。酵母双杂、双分子荧光互补和免疫共沉淀实验表明，MdTCP17和MdWOX11之间存在互作，而且MdWOX11的表达与不定根形成之间存在显著关联。MdWOX11过表达促进苹果中不定根原基的形成，而MdWOX11的干扰株系表现出不定根原基形成受到抑制的表型。此外，MdWOX11和MdLBD29基因的表达量存在正相关，酵母单杂、双荧光素酶报告和ChIP-qPCR实验表明MdWOX11可以结合到MdLBD29启动子的一个WOX-box元件上。此外，MdTCP17降低了MdWOX11对MdLBD29启动子的结合，并且MdTCP17和MdWOX11的共表达能够降低MdLBD29的表达水平。综上，本文的研究结果揭示了细胞分裂素响应基因MdTCP17介导的不定根形成抑制机制，为了可用于苹果砧木的遗传改良。

** 张 东 **