背景回顾：Auxin and brassinosteroids (BRs) are two major growth-promoting phytohormones that shape hypocotyl elongation; however, the cross-talk between auxin and BR in this process is not fully understood. 

主要发现：In this study, we found that auxin-induced hypocotyl elongation is dependent on brassinazole-resistant 1 (BZR1), a core BR signaling component. 

结果1-生长素促进的BZR1核积累依赖于MPK3/6：Auxin promotes BZR1 nuclear accumulation in hypocotyl cells, a process dependent on mitogen-activated protein kinase 3 (MPK3) and MPK6, which are both activated by auxin and whose encoding genes are highly expressed in hypocotyls. 

结果2-MPK3/6-GRF4-BZR1：We determined that MPK3/MPK6 phosphorylate and reduce the protein stability of general regulatory factor 4 (GRF4), a member of the 14-3-3 family of proteins that retain BZR1 in the cytoplasm.  

结论：In summary, this study reveals the molecular mechanism by which auxin promotes hypocotyl elongation by enhancing BZR1 nuclear accumulation via MPK3/MPK6-regulated GRF4 protein stability.

生长素和油菜素内酯（BRs）是两类主要的植物生长促进激素，能够塑造下胚轴的伸长；但是，生长素和BR在该过程中的信号交联并不清楚。本文中，作者发现生长素诱导的下胚轴伸长依赖于BR信号转导的核心组分BZR1。生长素促进下胚轴细胞中BZR1的核积累，而该过程依赖于MPK3和MPK6，MPK3/6又受到生长素的激活并且其编码基因在下胚轴中高表达。作者发现MPK3/MPK6能够磷酸化GRF4并降低后者的蛋白稳定性，GRF4是14-3-3家族的一个成员，其能够将BZR1滞留在胞质中。综上，本文的研究揭示了生长素通过MPK3/MPK6调控的GRF4蛋白稳定性，从而增强BZR1在核中的积累，进而促进下胚轴伸长的分子机制。

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