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，对其病原菌交替孢霉（Alternaria alternata）敏感。acr毒素的靶点是粗柠檬的线粒体，毒素对抗性植株的线粒体没有影响。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。该基因编码区位于线粒体基因组tRNA-Ala的II组内含子上，将成孔寡量受体转化为acr -毒素。ACRS基因位于毒素敏感和不敏感柑橘的线粒体基因组中。然而，在毒素不敏感的柑橘中，转录本遭受了功能失调的处理，而在毒素敏感的粗柠檬中，转录本在没有处理的情况下保持完整。为了确定ACRS是否在线粒体中翻译，我们用抗ACRS抗体对毒素敏感的粗柠檬和不敏感的柑橘分离的线粒体蛋白进行了免疫印迹分析。抗体在印迹上只能从粗糙的柠檬线粒体中检测到肽，而在任何抗性柑橘线粒体中抗体都不能检测到肽。这些结果表明，线粒体ACRS基因的转录后修饰调节了毒素与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ACRS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.