TTL proteins scaffold brassinosteroid signaling components at the plasma membrane to optimize signal transduction in Arabidopsis

First author: Vitor Amorim-Silva; Affiliations: Malaga University (马拉加大学): Malaga, Spain

Corresponding author: Miguel A. Botella

Brassinosteroids (BRs) form a group of steroidal hormones essential for plant growth, development and stress responses. BRs are perceived extracellularly by plasma membrane receptor-like kinases, which activates an interconnected signal transduction cascade, leading to the transcriptional regulation of BR-responsive genes. TETRATRICOPEPTIDE THIOREDOXIN-LIKE (TTL) genes are specific for land plants and their encoded proteins are defined by the presence of protein-protein interaction motives, i.e. an intrinsic disordered region at the N-terminus, six tetraticopeptide repeat domains and a C-terminus with homology to thioredoxins, thus likely mediating the assembly of multiprotein complexes. Phenotypic, molecular and genetic analyses show that TTL proteins are positive regulators of BR signaling in Arabidopsis. TTL3 directly interacts with a constitutively active BRI1 receptor kinase, BSU1 phosphatase and the BZR1 transcription factor and associates with BSK1, BIN2 kinases but not with BAK1. A functional TTL3-GFP shows dual cytoplasmic-plasma membrane localization. Depleting the endogenous BR content reduces plasma membrane localization of TTL3-GFP, while increasing BR content causes its plasma membrane relocalization, where it strengthens the association of BR signaling components. Our results reveal that TTL proteins promote BR responses and suggest that may function as scaffold proteins by bringing together cytoplasmic and plasma membrane BR signaling components.

油菜素内酯BRs是一类类固醇激素，对于植物生长、发育和胁迫响应均有非常重要的作用。BR能够被质膜类受体激酶在细胞外感知，从而激活互联信号转导级联，导致BR响应基因的转录调控。TTL基因是一类陆地植物特有的基因家族，其编码的蛋白在N端具有一段无序的区域，能够发生蛋白-蛋白互作，中间存在6个四肽重复结构域，C端序列与硫氧还蛋白同源，所以TTL很有可能介导多蛋白复合体的组装。表型、分子和遗传学分析显示TTL蛋白能够正向调控拟南芥中的BR信号。TTL3能够直接与组成型活性BRI1受体激酶、BSU1磷酸酶以及BZR1转录因子发生互作，并且与BSK1和BIN2激酶相关，并与BAK1并不关联。TTL3-GFP显示胞质-质膜的双重定位。降低内源性的BR含量会减少TTL3-GFP在质膜上的定位，而增加BR含量则会导致TTL3-GFP定位于质膜，TTL3-GFP在质膜上的强度与BR信号组份相关。本文的结果揭示了TTL蛋白能够促进BR响应，并且可能作为支架蛋白将胞质和纸膜上BR信号组份联系到一起。

通讯：Miguel A. Botella

个人简介：1984年，普渡大学和马拉加大学，生物化学博士。

研究方向：利用分子遗传学方法，采用拟南芥和西红柿等模式植物研究植物抵御环境压力的机制。

doi: https://doi.org/10.1105/tpc.19.00150

Journal: Plant Cell

First Published: June 12, 2019