背景回顾：The MADS transcription factors (TF) are an ancient eukaryotic protein family. In plants, the family is divided into two main lineages. 

主要发现：Here, we demonstrate that DNA binding in both lineages absolutely requires a short amino acid sequence C-terminal to the MADS domain (M domain) called the Intervening domain (I domain) that was previously defined only in type II lineage MADS. 

结果1-结构分析：Structural elucidation of the MI domains from the floral regulator, SEPALLATA3 (SEP3), shows a conserved fold with the I domain acting to stabilise the M domain.

结果2-结构域互换：Using the floral organ identity MADS TFs, SEP3, APETALA1 (AP1) and AGAMOUS (AG), domain swapping demonstrate that the I domain alters genome-wide DNA-binding specificity and dimerisation specificity.

结果3-功能互补试验：Introducing AG carrying the I domain of AP1 in the Arabidopsis ap1 mutant resulted in strong complementation and restoration of first and second whorl organs. 

结论：Taken together, these data demonstrate that the I domain acts as an integral part of the DNA-binding domain and significantly contributes to the functional identity of the MADS TF.

 摘 要 

MADS转录因子是一类古老的真核生物蛋白家族。在植物中，该家族的基因主要分为两个支系。本文中，作者发现这两个支系的MADS蛋白发挥功能都需要MADS（M）结构域C端的一段短的氨基酸序列，称之为Intervening（I）结构域，之前的研究认为该结构域仅在II类MADS蛋白支系中存在。对于开花调控蛋白SEP3的MI结构域的结构解析显示，MI结构域存在一个比较保守的折叠方式，其中I结构域起到稳定M结构域的作用。利用花器官决定基因SEP3、AP1和AG，作者通过互换结构域试验，发现I结构域改变了目的蛋白的全基因组上结构DNA的特异性和二聚化的特异性。以拟南芥的ap1突变体为背景，引入具有AP1蛋白I结构域的AG基因能够很好地互补并拯救ap1突变体花第一轮和第二轮器官的缺陷。综上，本文的研究结果揭示了I结构域作为MADS转录因子的DNA结合结构域组成部分发挥作用，并且能够显著作用于MADS转录因子的生物学功能。