背景回顾：Auxin plays pleiotropic roles in plant development via gene regulation upon its perception by the receptors TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALING F-BOX (TIR1/AFBs). This auxin-regulated transcriptional control mechanism originated in the common ancestor of land plants. 

提出问题：Although the complete loss of TIR1/AFBs causes embryonic lethality in Arabidopsis thaliana, it is unclear whether the requirement for TIR1-mediated auxin perception in cell viability can be generalized. 

主要研究：The model liverwort Marchantia polymorpha has a minimal auxin signaling system with only a single TIR1/AFB, MpTIR1. Here we show by genetic, biochemical, and transcriptomic analyses that MpTIR1 functions as an evolutionarily conserved auxin receptor. 

结果1-突变体表型：Null mutants and conditionally knocked-out mutants of MpTIR1 were viable but incapable of forming any organs and grew as cell masses. 

结果2-MpTIR1参与的生物学进程：Principal component analysis performed using transcriptomes at various developmental stages indicated that MpTIR1 is involved in the developmental transition from spores to organized thalli, during which apical notches containing stem cells are established. In Mptir1 cells, stem-cell- and differentiation-related genes were up- and down-regulated, respectively. 

结论：Our findings suggest that, in M. polymorpha, auxin signaling is dispensable for cell division but is essential for three-dimensional patterning of the plant body by establishing pluripotent stem cells for organogenesis, a derived trait of land plants.

 摘 要 

提生长素通过其在植物中的受体TIR1/AFBs作用于基因调控，从而在植物的发育过程中发挥多效性作用。生长素调控的转录调控机制起源于陆地植物共同的祖先。尽管TIR1/AFBs的完全缺失会导致拟南芥的胚胎致死，但是仍不清楚TIR1介导的生长素感知对细胞存活的必需性是否具有普遍性。模式苔藓植物地钱具有一套最小的生长素信号转导系统，仅包含一个TIR/AFB，即MpTIR1。本文中，作者通过遗传学、生物化学以及转录组学分析，揭示了MpTIR1作为一个演化上保守的生长素受体发挥作用。MpTIR1基因的无效突变体以及条件性敲除突变体可以存活，但是不能再形成新的器官，而是以细胞团的方式进行生长。用不同发育阶段的转录组进行主成分分析，发现MpTIR1参与了从孢子到叶状体的发育转变，在此过程中含有干细胞的顶端缺口被成功建立。在Mptir1细胞中，干细胞和分化相关的基因分别呈上调和下调表达。本文的研究结果显示在地钱中，生长素信号转导对于细胞分裂是可有可无的，但是其能够通过建立多能干细胞作用于器官发生，因此对于植物体的三维模式建成是必不可少的。