Cloning and Evaluation of Receptor Gene for Host-selective ACR Toxin

粗柠檬对寄主选择性毒素ACR-毒素敏感，对粗柠檬致病型链格孢菌（Alternaria alternata）敏感。ACR毒素的作用靶点是粗柠檬酸，对抗性植物的线粒体没有影响。我们克隆了一个受体基因ACRS基因，该基因通过在大肠杆菌细胞中表达而赋予毒素敏感性。该基因的编码区位于线粒体基因组中tRNA-Ala的第II组内含子中，负责将成孔寡聚受体翻译成ACR毒素。ACRS基因定位于毒素敏感和不敏感柑橘的线粒体基因组中。然而，转录物在毒素不敏感的柑橘中受到加工而功能失调，而在毒素敏感的粗糙柠檬中的转录物在没有加工的情况下保持完整。为了确定ACRS是否在线粒体中翻译，用抗ACRS抗体通过蛋白质印迹分析来自毒素敏感的粗柠檬和不敏感的柑橘的分离的线粒体的蛋白质。该抗体在印迹上仅检测到来自粗糙柠檬线粒体的肽，而来自所测试的任何抗性柑橘线粒体的抗体未检测到肽。这些结果表明，该线粒体ACRS基因的转录后修饰调节毒素-植物相互作用的特异性，其中线粒体中的RNA加工在控制柑橘对ACR毒素的敏感性中起关键作用。

Rough lemon is sensitive to host-selective toxin ACR-toxin and susceptible to its producer Alternaria alternata rough lemon pathotype. The target site of ACR-toxin is rough lemon mitochondrion, and the toxin has no effect on mitochondria from resistant plants. We have cloned a receptor gene, ACRS gene, which confers the toxin sensitivity by expressing in Escherichia coli cells. Coding region of the gene is located in the group II intron of tRNA-Ala in mitochondrial genome, and translates the pore-forming oligometric receptor to ACR-toxin. ACRS gene locates at mitochondrial genomes from both toxin-sensitive and insensitive citrus. However, the transcripts suffer a processing to be dysfunctional in toxin-insensitive citrus, while those in toxin-sensitive rough lemon remain intact without the processing. To determine whether ACRS is translated in mitochondria, proteins from isolated mitochondria of toxin-sensitive rough lemon and insensitive citrus were analyzed by western blot with anti-ACRS antibodies. The antibodies detected peptides on blot from only rough lemon mitochondria, while no peptides detected by the antibodies from any resistant citrus mitochondria tested. These results demonstrated that the post-transcriptional modification of this mitochondrial ACRS gene regulates specificity in the toxin-plant interactions, in which RNA processing in mitochondria plays a key role in controlling sensitivity to ACR-toxin in citrus.