Tomato is a major cultivated vegetable species of great economic importance throughout the world, but its fruit yield is severely impaired by drought stress. PopW, a harpin protein from Ralstonia solanacearum ZJ3721, plays vital roles in various plant defence responses and growth. In this study, we observed that the foliar application of PopW increased tomato drought tolerance. Our results showed that compared with water-treated plants, PopW-treated plants presented a significantly higher recovery rate and leaf relative water content under drought-stress conditions. PopW decreased the malondialdehyde content and relative electrical conductivity by 40.2% and 21%, respectively. Drought disrupts redox homeostasis through the excessive accumulation of reactive oxygen species (ROS). PopW-treated plants displayed an obvious reduction in ROS accumulation due to enhanced activities of the antioxidant enzyme catalase, superoxide dismutase and peroxidase. Moreover, PopW promoted early stomatal closure, thereby minimizing the water loss rate of plants under drought stress. Further investigation revealed that endogenous abscisic acid (ABA) levels and the transcript levels of drought-responsive genes involved in ABA signal transduction pathways increased in response to PopW. These results confirm that PopW increases drought tolerance through multiple mechanisms involving an enhanced water-retention capacity, balanced redox homeostasis, increased osmotic adjustment, reduced membrane damage and decreased stomatal aperture, suggesting that the application of exogenous PopW may be a potential method to enhance tomato drought tolerance.

番茄是一种在世界范围内具有重要经济意义的主要栽培蔬菜品种，但其果实产量受到干旱胁迫的严重影响。PopW，一种来自青枯病菌的 harpin 蛋白ZJ3721，在各种植物防御反应和生长中起着至关重要的作用。在这项研究中，我们观察到叶面喷施 PopW 提高了番茄的耐旱性。我们的结果表明，与水处理的植物相比，PopW 处理的植物在干旱胁迫条件下表现出显着更高的恢复率和叶片相对含水量。PopW 使丙二醛含量和相对电导率分别降低了 40.2% 和 21%。干旱会通过活性氧 (ROS) 的过度积累破坏氧化还原稳态。由于抗氧化酶过氧化氢酶、超氧化物歧化酶和过氧化物酶的活性增强，经 PopW 处理的植物表现出 ROS 积累的明显减少。此外，PopW 促进了气孔早期关闭，从而最大限度地减少干旱胁迫下植物的失水率。进一步的研究表明，内源脱落酸 (ABA) 水平和参与 ABA 信号转导途径的干旱响应基因的转录水平响应 PopW 增加。这些结果证实，PopW 通过多种机制提高耐旱性，包括增强保水能力、平衡氧化还原稳态、增加渗透调节、减少膜损伤和减少气孔孔径，表明外源性 PopW 的应用可能是增强番茄的潜在方法耐旱性。