Effector-Triggered Immunity Determines Host Genotype-Specific Incompatibility in Legume-Rhizobium Symbiosis.
Effector-Triggered Immunity Determines Host Genotype-Specific Incompatibility in Legume-Rhizobium Symbiosis.
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DOI：
10.1093/pcp/pcw104
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发表时间：
2016-08
影响因子：
4.9
通讯作者：
M. Yasuda;H. Miwa;Sachiko Masuda;Yumiko Takebayashi;H. Sakakibara;Shin Okazaki
中科院分区：
文献类型：
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作者：
M. Yasuda;H. Miwa;Sachiko Masuda;Yumiko Takebayashi;H. Sakakibara;Shin Okazaki
豆科植物和根瘤菌之间的共生导致固氮根瘤的形成。在大豆中，几个宿主基因，称为Rj基因，控制着结瘤。携带Rj 4基因的大豆品种限制了特定根瘤菌如埃氏慢生根瘤菌的产孢。elkanii具有功能性III型分泌系统（T3 SS），已知其通过病原菌递送毒力因子。在本研究中，我们研究了Rj 4大豆中T3 SS依赖的促排限制的分子基础。接种试验表明，大豆品种BARC-2（Rj 4/Rj 4）能抑制B的侵染。elkanii USDA 61，而其近等基因系BARC-3（rj 4/rj 4）与同一菌株形成固氮根瘤。在接种USDA 61的BARC-2根中未观察到根毛卷曲和侵染线，表明Rj 4阻断了B。在早期阶段的埃卡尼感染。在接种USDA 61的BARC-2的根中观察到H2 O2和水杨酸（SA）的积累。转录组分析表明，接种USDA 61，而不是其在BARC-2中的T3 SS突变体，诱导防御相关基因，包括那些编码超敏诱导的反应蛋白，其作用于效应触发免疫（ETI）在拟南芥。这些结果表明，B。elkanii T3 SS在Rj 4大豆中触发SA介导的ETI型反应，从而阻断共生相互作用。这项研究揭示了植物-病原体和植物-共生体相互作用的共同分子机制，并表明根瘤共生的建立需要逃避或抑制根瘤菌效应物引发的植物免疫反应。
Symbiosis between legumes and rhizobia leads to the formation of N2-fixing root nodules. In soybean, several host genes, referred to as Rj genes, control nodulation. Soybean cultivars carrying the Rj4 gene restrict nodulation by specific rhizobia such as Bradyrhizobium elkanii We previously reported that the restriction of nodulation was caused by B. elkanii possessing a functional type III secretion system (T3SS), which is known for its delivery of virulence factors by pathogenic bacteria. In the present study, we investigated the molecular basis for the T3SS-dependent nodulation restriction in Rj4 soybean. Inoculation tests revealed that soybean cultivar BARC-2 (Rj4/Rj4) restricted nodulation by B. elkanii USDA61, whereas its nearly isogenic line BARC-3 (rj4/rj4) formed nitrogen-fixing nodules with the same strain. Root-hair curling and infection threads were not observed in the roots of BARC-2 inoculated with USDA61, indicating that Rj4 blocked B. elkanii infection in the early stages. Accumulation of H2O2 and salicylic acid (SA) was observed in the roots of BARC-2 inoculated with USDA61. Transcriptome analyses revealed that inoculation of USDA61, but not its T3SS mutant in BARC-2, induced defense-related genes, including those coding for hypersensitive-induced responsive protein, which act in effector-triggered immunity (ETI) in Arabidopsis. These findings suggest that B. elkanii T3SS triggers the SA-mediated ETI-type response in Rj4 soybean, which consequently blocks symbiotic interactions. This study revealed a common molecular mechanism underlying both plant-pathogen and plant-symbiont interactions, and suggests that establishment of a root nodule symbiosis requires the evasion or suppression of plant immune responses triggered by rhizobial effectors.