Plants trigger appropriate defense responses, notably, through intracellular nucleotide-binding (NB) and leucine-rich repeat (LRR)-containing receptors (NLRs) that detect secreted pathogen effector proteins. In NLR resistance genes, the toll/interleukin-1 receptor (TIR)-NB-LRR proteins (TNLs) are an important subfamily, out of which approximately half the members carry a post-LRR (PL) domain of unknown role. We first investigated the requirement of the PL domain for TNL-mediated immune response by mutating the most conserved amino acids across PL domains of Arabidopsis thaliana TNLs. We identified several amino acids in the PL domain of RPS4, required for its ability to trigger a hypersensitive response to AvrRps4 in a Nicotiana tabacum transient assay. Mutating the corresponding amino acids within the PL domain of the tobacco TNL gene N also affected its function. Consequently, our results indicate that the integrity of the PL domain at conserved positions is crucial for at least two unrelated TNLs. We then tested the PL domain specificity for function by swapping PL domains between the paralogs RPS4 and RPS4B. Our results suggest that the PL domain is involved in their TNL pair specificity, ‘off state’ stability, and NLR complex activation. Considering genetically paired Arabidopsis TNLs, we finally compared the PL and TIR domains of their sensor and executor sequences, respectively. While TIR and PL domains from executors present complete motifs, sensors showed a lack of conservation with degenerated motifs. We here provide a contribution to the functional analysis of the PL domain in order to decipher its role for TNL function.

Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

植物触发适当的防御反应，特别是通过细胞内核苷酸结合（NB）和富含亮氨酸重复序列（LRR）的受体（NLR）来检测分泌的病原体效应蛋白。在 NLR 抗性基因中，Toll/白细胞介素 1 受体 (TIR)-NB-LRR 蛋白 (TNL) 是一个重要的亚家族，其中大约一半的成员携带作用未知的后 LRR (PL) 结构域。我们首先通过突变拟南芥TNL 的 PL 结构域中最保守的氨基酸来研究 PL 结构域对 TNL 介导的免疫反应的需求。我们鉴定了 RPS4 PL 结构域中的几个氨基酸，这些氨基酸是 RPS4 在烟草瞬时测定中触发对 AvrRps4 过敏反应的能力所必需的。烟草TNL基因N的PL结构域内相应氨基酸的突变也会影响其功能。因此，我们的结果表明，保守位置处 PL 结构域的完整性对于至少两个不相关的 TNL 至关重要。然后，我们通过在旁系同源物RPS4和RPS4B之间交换 PL 结构域来测试 PL 结构域的功能特异性。我们的结果表明 PL 结构域参与其 TNL 对特异性、“关闭状态”稳定性和 NLR 复合物激活。考虑到基因配对的拟南芥TNL，我们最终分别比较了它们的传感器和执行器序列的 PL 和 TIR 域。虽然来自执行器的 TIR 和 PL 结构域呈现完整的基序，但传感器显示出退化基序缺乏保守性。我们在此对 PL 结构域的功能分析做出贡献，以破译其在 TNL 功能中的作用。

版权所有 © 2021 作者。这是一篇根据 CC BY-NC-ND 4.0 国际许可证分发的开放获取文章。