SMALL AUXIN-UP RNAs (SAURs) comprise the largest family of early auxin response genes. Some SAURs have been reported to play important roles in plant growth and development, but their functional relationships with auxin signaling remain unestablished. Here, we report Arabidopsis (Arabidopsis thaliana) SAUR15 acts downstream of the auxin response factors ARF6,8 and ARF7,19 to regulate auxin signaling-mediated lateral root (LR) and adventitious root (AR) formation. The loss-of-function mutant saur15-1 exhibits fewer LRs and ARs. By contrast, plants overexpressing SAUR15 exhibit more LRs and ARs. We find that the SAUR15 promoter contains four tandem auxin-responsive elements, which are directly bound by ARF6 and ARF7 and are essential for SAUR15 expression. LR and AR impairment in arf6 and arf7 mutants is partially reduced by ectopic expression of SAUR15. Additionally, we demonstrate that the ARF6,7-upregulated SAUR15 promotes LR and AR development using two mechanisms. On the one hand, SAUR15 interacts with PP2C-D subfamily type 2C protein phosphatases to inhibit their activities, thereby stimulating plasma membrane H⁺-ATPases, which drives cell expansion and facilitates LR and AR formation. On the other hand, SAUR15 promotes auxin accumulation, potentially by inducing the expression of auxin biosynthesis genes. A resulting increase in free auxin concentration likely triggers LR and AR formation, forming a feedback loop. Our study provides insights and a better understanding of how SAURs function at the molecular level in regulating auxin-mediated LR and AR development.

SMALL AUXIN-UP RNA ( SAUR ) 包含最大的早期生长素反应基因家族。据报道，一些 SAUR 在植物生长和发育中发挥重要作用，但它们与生长素信号传导的功能关系尚未确定。在这里，我们报道拟南芥（ Arabidopsis thaliana ） SAUR15作用于生长素反应因子ARF6,8和ARF7,19的下游，调节生长素信号介导的侧根（LR）和不定根（AR）的形成。功能丧失突变体saur15-1表现出较少的 LR 和 AR。相比之下，过度表达SAUR15的植物表现出更多的 LR 和 AR。我们发现SAUR15启动子含有四个串联的生长素响应元件，它们直接与ARF6和ARF7结合，对于SAUR15的表达至关重要。 SAUR15的异位表达部分减少了arf6和arf7突变体中的 LR 和 AR 损伤。此外，我们证明 ARF6,7 上调的 SAUR15 通过两种机制促进 LR 和 AR 发育。一方面，SAUR15与PP2C-D亚家族2C型蛋白磷酸酶相互作用，抑制其活性，从而刺激质膜H ⁺ -ATP酶，驱动细胞扩张，促进LR和AR形成。另一方面，SAUR15 可能通过诱导生长素生物合成基因的表达来促进生长素积累。由此产生的游离生长素浓度的增加可能会触发 LR 和 AR 的形成，形成反馈循环。我们的研究提供了见解并更好地理解 SAUR 如何在分子水平上调节生长素介导的 LR 和 AR 发育。