In plants, NLR immune receptors generally exhibit hallmarks of rapid evolution even at the intraspecific level. We used iterative sequence similarity searches coupled with phylogenetic analyses to reconstruct the evolutionary history of ZAR1, an atypically conserved NLR that traces its origin to early flowering plant lineages ∼220 to 150 million years ago (Jurassic period). We discovered 120 ZAR1 orthologs in 88 species, including the monocot Colacasia esculenta, the magnoliid Cinnamomum micranthum and the majority of eudicots, notably the early diverging eudicot species Aquilegia coerulea. Ortholog sequence analyses revealed highly conserved features of ZAR1, including regions for pathogen effector recognition, intramolecular interactions and cell death activation. We functionally reconstructed the cell death activity of ZAR1 and its partner receptor-like cytoplasmic kinase (RLCK) from distantly related plant species, experimentally validating the hypothesis that ZAR1 has evolved to be a partner with RLCKs early in its evolution. In addition, ZAR1 acquired novel features, such as a C-terminal integration of a thioredoxin-like domain. ZAR1 duplicated into two paralog families, which underwent distinct evolutionary paths. We conclude that ZAR1 stands out among angiosperm NLRs for having experienced relatively limited gene duplication and expansion throughout its deep evolutionary history. Nonetheless, ZAR1 did also give rise to non-canonical NLR proteins with integrated domains and degenerated molecular features.

中文翻译：

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侏罗纪 NLR：非典型古代免疫受体 ZAR1 的保守和动态进化特征

在植物中，NLR 免疫受体通常表现出快速进化的特征，即使在种内水平也是如此。我们使用迭代序列相似性搜索和系统发育分析来重建 ZAR1 的进化历史，ZAR1 是一种非典型保守的 NLR，其起源可追溯到 220 至 1.5 亿年前（侏罗纪时期）的早期开花植物谱系。我们在 88 个物种中发现了 120 个 ZAR1 直系同源物，包括单子叶植物Colacasia esculenta、木兰科植物Cinnamomum micranthum和大多数真双子叶植物，尤其是早期分化的真双子叶植物Aquilegia coerulea. 直系同源序列分析揭示了 ZAR1 的高度保守特征，包括病原体效应识别、分子内相互作用和细胞死亡激活的区域。我们在功能上重建了来自远缘植物物种的 ZAR1 及其伴侣受体样细胞质激酶 (RLCK) 的细胞死亡活性，通过实验验证了 ZAR1 在其进化早期已进化为 RLCK 伴侣的假设。此外，ZAR1 获得了新的特征，例如硫氧还蛋白样结构域的 C 端整合。ZAR1 复制成两个旁系同源家族，它们经历了不同的进化路径。我们得出结论，ZAR1 在被子植物 NLR 中脱颖而出，因为在其整个进化历史中经历了相对有限的基因复制和扩展。尽管如此，