Functional diversification of Arabidopsis SEC1-related SM proteins in cytokinetic and secretory membrane fusion

First author: Matthias Karnahl; Affiliations: University of Tübingen (图宾根大学): Tübingen, Germany

Corresponding author: Gerd Jürgens

Sec1/Munc18 (SM) proteins contribute to membrane fusion by interacting with Qa-SNAREs or nascent trans-SNARE complexes. Gymnosperms and the basal angiosperm Amborella have only a single SEC1 gene related to the KEULE gene in Arabidopsis. However, the genomes of most angiosperms including Arabidopsis encode three SEC1-related SM proteins of which only KEULE has been functionally characterized as interacting with the cytokinesis-specific (胞质分裂) Qa-SNARE KNOLLE during cell-plate (细胞板) formation. Here we analyze the closest paralog of KEULE named SEC1B. In contrast to the cytokinesis defects of keule mutants, sec1b mutants are homozygous viable (能养活的). However, the keule sec1b double mutant was nearly gametophytically lethal (配子体致死), displaying collapsed pollen grains, which suggests substantial overlap between SEC1B and KEULE functions in secretion-dependent growth. SEC1B had a strong preference for interaction with the evolutionarily ancient Qa-SNARE SYP132 involved in secretion (分泌) and cytokinesis, whereas KEULE interacted with both KNOLLE and SYP132. This differential interaction with Qa-SNAREs is likely conferred by domains 1 and 2a of the two SM proteins. Comparative analysis of all four possible combinations of the relevant SEC1 Qa-SNARE double mutants revealed that in cytokinesis, the interaction of SEC1B with KNOLLE plays no role, whereas the interaction of KEULE with KNOLLE is prevalent and functionally as important as the interactions of both SEC1B and KEU with SYP132 together. Our results suggest that functional diversification of the two SEC1-related SM proteins during angiosperm evolution resulted in enhanced interaction of SEC1B with Qa-SNARE SYP132, and thus a predominant role of SEC1B in secretion.

Sec1/Munc18（SM）蛋白通过与Qa-SNARE或者trans-SNARE复合物互作从而作用于膜融合。裸子植物和基础被子植物无柚樟均只有一个SEC1基因，与拟南芥中的KEULE基因同源。大多数的被子植物，包括拟南芥均含有三个SEC1相关的SM蛋白编码基因，而KEULE经过功能鉴定确认在细胞板形成时与胞质分裂特异性Qa-SNARE KNOLLE蛋白互作。本文分析了与KEULE最为旁系同源的蛋白SEC1B。与keule突变体表现出胞质分裂缺陷不同，sec1b突变体的纯合植株不致死。然而，keule sec1b双突变体接近配子体致死，并且花粉粒失活，说明SEC1B和KEULE蛋白在植物依赖于分泌的生长中存在很大程度的功能冗余。SEC1B更加偏向于与进化上比较古老的Qa-SNARE SYP132相互作用，该蛋白作用于分泌和胞质分裂，而KEULE蛋白则与KNOLLE和SYP132都相互作用。这两个SM蛋白上的1和2a结构域可能导致了其与Qa-SNARE不同的互作能力。对4个组合的SEC1 Qa-SNARE双突变体的比较分析显示在胞质分裂过程中SEC1B与KNOLLE的互作不发挥作用，而KEULE与KNOLLE的互作则比较普遍，且和SEC1B与SYP132、KEU与SYP132的互作在功能上同样重要。本文的结果表明在被子植物演化过程中这两个SEC1相关的SM蛋白的功能分化导致了SEC1B与Qa-SNARE SYP132的互作增强，进而SEC1B的功能主要作用于分泌。

通讯：Gerd Jürgens(http://www.zmbp.uni-tuebingen.de/dev-genetics/juergens/people.html)

研究方向：植物中的囊泡形成与融合。

doi: https://doi.org/10.1073/pnas.1722611115

Journal: PNAS

Published online: 29 May, 2018

（P.S. 原文下载：链接:https://pan.baidu.com/s/1qFiSsqwlF_7JjmGMbedfhQ  密码:dmu6）