The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA.
BMC Plant Biol. 2013 Dec 6;13:204. doi: 10.1186/1471-2229-13-204.
Arabidopsis thaliana (Arabidopsis) NON-EXPRESSOR OF PR1 (NPR1) is a transcription coactivator that plays a central role in regulating the transcriptional response to plant pathogens. Developing flowers of homozygous npr3 mutants are dramatically more resistant to infection by the pathogenic bacterium Pseudomonas syringae, suggesting a role of NPR3 as a repressor of NPR1-mediated defense response with a novel role in flower development.
We report here the characterization of a putative NPR3 gene from the tropical tree species Theobroma cacao (TcNPR3). Like in Arabidopsis, TcNPR3 was constitutively expressed across a wide range of tissue types and developmental stages but with some differences in relative levels compared to Arabidopsis. To test the function of TcNPR3, we performed transgenic complementation analysis by introducing a constitutively expressing putative TcNPR3 transgene into an Arabidopsis npr3 mutant. TcNPR3 expressing Arabidopsis plants were partially restored to the WT pathogen phenotype (immature flowers susceptible to bacterial infection). To test TcNPR3 function directly in cacao tissues, a synthetic microRNA targeting TcNPR3 mRNA was transiently expressed in cacao leaves using an Agrobacterium-infiltration method. TcNPR3 knock down leaf tissues were dramatically more resistance to infection with Phytophthora capsici in a leaf bioassay, showing smaller lesion sizes and reduced pathogen replication.
We conclude that TcNPR3 functions similar to the Arabidopsis NPR3 gene in the regulation of the cacao defense response. Since TcNPR3 did not show a perfect complementation of the Arabidopsis NPR3 mutation, the possibility remains that other functions of TcNPR3 remain to be found. This novel knowledge can contribute to the breeding of resistant cacao varieties against pathogens through molecular markers based approaches or biotechnological strategies.
拟南芥（Arabidopsis）非表达蛋白 1（NPR1）是一种转录共激活因子，在调节植物病原体的转录反应中发挥核心作用。纯合 npr3 突变体的发育花朵对病原菌丁香假单胞菌的感染具有显著的抗性，这表明 NPR3 作为 NPR1 介导的防御反应的抑制剂发挥作用，并在花发育中具有新的作用。
我们在这里报道了来自热带树种可可（Theobroma cacao）的一种假定 NPR3 基因（TcNPR3）的特征。与拟南芥一样，TcNPR3 在广泛的组织类型和发育阶段中持续表达，但与拟南芥相比，相对水平存在一些差异。为了测试 TcNPR3 的功能，我们通过将一个组成型表达的假定 TcNPR3 转基因引入拟南芥 npr3 突变体中进行了转基因互补分析。表达 TcNPR3 的拟南芥植物在一定程度上恢复为 WT 病原体表型（不成熟的花朵易受细菌感染）。为了直接在可可组织中测试 TcNPR3 的功能，使用农杆菌浸润方法在可可叶片中瞬时表达了针对 TcNPR3 mRNA 的合成 microRNA。在叶片生物测定中，TcNPR3 敲低的叶片组织对辣椒疫霉的感染具有显著的抗性，表现为较小的病变大小和减少的病原体复制。
我们得出结论，TcNPR3 与拟南芥 NPR3 基因在可可防御反应的调节中具有相似的功能。由于 TcNPR3 没有完全互补拟南芥 NPR3 突变，因此仍然有可能发现 TcNPR3 的其他功能。这种新的知识可以通过基于分子标记的方法或生物技术策略为培育对病原体具有抗性的可可品种做出贡献。
