Todesco Marco, Kim Sang-Tae, Chae Eunyoung, Bomblies Kirsten, Zaidem Maricris, Smith Lisa M, Weigel Detlef, Laitinen Roosa A E
Department of Molecular Biology, Max Planck Institute for Developmental Biology, Tübingen, Germany.
PLoS Genet. 2014 Jul 10;10(7):e1004459. doi: 10.1371/journal.pgen.1004459. eCollection 2014 Jul.
A fundamental question in biology is how multicellular organisms distinguish self and non-self. The ability to make this distinction allows animals and plants to detect and respond to pathogens without triggering immune reactions directed against their own cells. In plants, inappropriate self-recognition results in the autonomous activation of the immune system, causing affected individuals to grow less well. These plants also suffer from spontaneous cell death, but are at the same time more resistant to pathogens. Known causes for such autonomous activation of the immune system are hyperactive alleles of immune regulators, or epistatic interactions between immune regulators and unlinked genes. We have discovered a third class, in which the Arabidopsis thaliana immune system is activated by interactions between natural alleles at a single locus, ACCELERATED CELL DEATH 6 (ACD6). There are two main types of these interacting alleles, one of which has evolved recently by partial resurrection of a pseudogene, and each type includes multiple functional variants. Most previously studies hybrid necrosis cases involve rare alleles found in geographically unrelated populations. These two types of ACD6 alleles instead occur at low frequency throughout the range of the species, and have risen to high frequency in the Northeast of Spain, suggesting a role in local adaptation. In addition, such hybrids occur in these populations in the wild. The extensive functional variation among ACD6 alleles points to a central role of this locus in fine-tuning pathogen defenses in natural populations.
生物学中的一个基本问题是多细胞生物如何区分自我和非自我。做出这种区分的能力使动植物能够检测病原体并做出反应，而不会触发针对自身细胞的免疫反应。在植物中，不适当的自我识别会导致免疫系统自主激活，使受影响的个体生长得较差。这些植物还会出现自发性细胞死亡，但同时对病原体更具抗性。已知这种免疫系统自主激活的原因是免疫调节因子的高活性等位基因，或免疫调节因子与非连锁基因之间的上位性相互作用。我们发现了第三类情况，其中拟南芥的免疫系统是由单个位点加速细胞死亡6（ACD6）的天然等位基因之间的相互作用激活的。这些相互作用的等位基因主要有两种类型，其中一种是最近通过假基因的部分复活进化而来的，每种类型都包括多个功能变体。以前大多数关于杂种坏死的研究涉及在地理上不相关的种群中发现的罕见等位基因。相反，这两种类型的ACD6等位基因在整个物种范围内都以低频率出现，并在西班牙东北部上升到高频率，表明其在局部适应中发挥作用。此外，这种杂种在这些野生种群中也会出现。ACD6等位基因之间广泛的功能变异表明该位点在自然种群中微调病原体防御方面发挥着核心作用。
