Abstract：
The importance of metacaspases in programmed cell death and tissue differentiation is known, but their significance in disease stress response, particularly in a crop plant, remained enigmatic. We show the tomato metacaspase expression landscape undergoes differential reprogramming during biotrophic and necrotrophic modes of pathogenesis; also, the metacaspase activity dynamics correlate with the disease progression. These stresses have contrasting effects on the expression pattern of SlMC8, a Type II metacaspase, indicating that SlMC8 is crucial for stress response. In accordance, selected biotic stress-related transcription factors repress SlMC8 promoter activity. Interestingly, SlMC8 exhibits maximum proteolysis at an acidic pH range of 5-6. Molecular dynamics simulation identified the low pH-driven protonation event of Glu246 as critical to stabilize the interaction of SlMC8 with its substrate. Mutagenesis of Glu246 to charge-neutral glutamine suppressed SlMC8\'s proteolytic activity, corroborating the importance of the amino acid in SlMC8 activation. The glutamic acid residue is found in an equivalent position in metacaspases having acidic pH dependence. SlMC8 overexpression leads to heightened ROS levels, cell death, and tolerance to PstDC3000, and SlMC8 repression reversed the phenomena. However, the overexpression of SlMC8 increases tomato susceptibility to necrotrophic Alternaria solani. We propose that SlMC8 activation due to concurrent changes in cellular pH during infection contributes to the basal resistance of the plant by promoting cell death at the site of infection, and the low pH dependence acts as a guard against unwarranted cell death. Our study confirms the essentiality of a low pH-driven Type II metacaspase in tomato biotic stress-response regulation.
摘要：
众所周知，在程序性细胞死亡和组织分化中，但是它们在疾病应激反应中的意义，特别是在农作物中，仍然神秘。我们展示了番茄metacaspase表达景观在发病机理的生物营养和坏死模式期间经历了差异重编程；此外，β-半胱天冬酶活性动力学与疾病进展相关。这些胁迫对SlMC8的表达模式有相反的影响，SlMC8是一种II型的β-半胱氨酸蛋白酶，表明SlMC8对应激反应至关重要。InAccording,选定的生物胁迫相关转录因子抑制SlMC8启动子活性。有趣的是,SlMC8在5-6的酸性pH范围内表现出最大的蛋白水解。分子动力学模拟确定了低pH驱动的Glu246质子化事件对于稳定SlMC8与其底物的相互作用至关重要。Glu246对电荷中性谷氨酰胺的诱变抑制了SlMC8的蛋白水解活性，证实了氨基酸在SlMC8活化中的重要性。谷氨酸残基在具有酸性pH依赖性的超半胱氨酸蛋白酶中的等效位置被发现。SlMC8过表达导致ROS水平升高，细胞死亡,对PstDC3000的耐受性和SlMC8抑制逆转了这一现象。然而,SlMC8的过表达增加了番茄对坏死性黑链孢菌的敏感性。我们建议，由于感染过程中细胞pH值的同时变化而引起的SlMC8激活通过促进感染部位的细胞死亡来促进植物的基础抗性，低pH依赖性可以防止不必要的细胞死亡。我们的研究证实了低pH值驱动的II型亚半胱氨酸蛋白酶在番茄生物应激反应调节中的重要性。
