Over 80,000 angiosperm species produce flowers with petals fused into a corolla tube. The corolla tube contributes to the tremendous diversity of flower morphology and plays a critical role in plant reproduction, yet it remains one of the least understood plant structures from a developmental genetics perspective. Through mutant analyses and transgenic experiments, we show that the tasiRNA-ARF pathway is required for corolla tube formation in the monkeyflower species Mimulus lewisii. Loss-of-function mutations in the M. lewisii orthologs of ARGONAUTE7 and SUPPRESSOR OF GENE SILENCING3 cause a dramatic decrease in abundance of TAS3-derived small RNAs and a moderate upregulation of AUXIN RESPONSE FACTOR3 (ARF3) and ARF4, which lead to inhibition of lateral expansion of the bases of petal primordia and complete arrest of the upward growth of the interprimordial regions, resulting in unfused corollas. Using the DR5 auxin-responsive promoter, we discovered that auxin signaling is continuous along the petal primordium base and the interprimordial region during the critical stage of corolla tube formation in the wild type, similar to the spatial pattern of MlARF4 expression. Auxin response is much weaker and more restricted in the mutant. Furthermore, exogenous application of a polar auxin transport inhibitor to wild-type floral apices disrupted petal fusion. Together, these results suggest a new conceptual model highlighting the central role of auxin-directed synchronized growth of the petal primordium base and the interprimordial region in corolla tube formation.

超过 80,000 种被子植物会产生花瓣融合成花冠管的花朵。花冠管促成了花朵形态的巨大多样性，并在植物繁殖中发挥着关键作用，但从发育遗传学的角度来看，它仍然是人们最不了解的植物结构之一。通过突变体分析和转基因实验，我们表明 tasiRNA- ARF途径是猴花种Mimulus lewisii花冠管形成所必需的。 ARGONAUTE7和SUPPRESSOR OF GENE SILENCING3的M. lewisii直系同源物中的功能丧失突变导致TAS3衍生的小 RNA 丰度急剧下降，以及AUXIN RESPONSE FACTOR3 ( ARF3 ) 和ARF4的中度上调，从而导致抑制花瓣原基基部横向扩张，原基间区域向上生长完全停止，导致花冠未融合。使用DR5生长素响应启动子，我们发现在野生型花冠管形成的关键阶段，生长素信号传导沿着花瓣原基基部和原基间区域是连续的，类似于MlARF4表达的空间模式。突变体中的生长素反应要弱得多且受到更多限制。此外，对野生型花顶端外源应用极性生长素转运抑制剂会破坏花瓣融合。总之，这些结果提出了一个新的概念模型，强调生长素引导的花瓣原基基部和原基间区域的同步生长在花冠管形成中的核心作用。