Stomata Prioritize Their Responses to Multiple Biotic and Abiotic Signal Inputs

Stomata are microscopic pores in leaf epidermis that regulate gas exchange between plants and the environment. Being natural openings on the leaf surface, stomata also serve as ports for the invasion of foliar pathogenic bacteria. Each stomatal pore is enclosed by a pair of guard cells that are able to sense a wide spectrum of biotic and abiotic stresses and respond by precisely adjusting the pore width. However, it is not clear whether stomatal responses to simultaneously imposed biotic and abiotic signals are mutually dependent on each other. Here we show that a genetically engineered Escherichia coli strain DH5α could trigger stomatal closure in Vicia faba, an innate immune response that might depend on NADPH oxidase-mediated ROS burst. DH5α-induced stomatal closure could be abolished or disguised under certain environmental conditions like low [CO2], darkness, and drought, etc. Foliar spraying of high concentrations of ABA could reduce stomatal aperture in high humidity-treated faba bean plants. Consistently, the aggressive multiplication of DH5α bacteria in Vicia faba leaves under high humidity could be alleviated by exogenous application of ABA. Our data suggest that a successful colonization of bacteria on the leaf surface is correlated with stomatal aperture regulation by a specific set of environmental factors.

气孔（stomata）是植物叶表皮上的微孔，负责调控植物与环境间的气体交换。作为叶表面的天然开口，气孔同时也是叶部病原细菌入侵的天然通道。每个气孔孔道由一对保卫细胞包围，这些保卫细胞能够感知广泛的生物与非生物胁迫，并通过精准调控孔道宽度做出响应。然而，目前尚不清楚植物气孔对同时施加的生物与非生物信号的响应是否相互依赖。本研究发现，一株基因工程大肠杆菌（Escherichia coli）菌株DH5α可诱导蚕豆（Vicia faba）产生气孔关闭，这一先天免疫反应可能依赖于NADPH氧化酶介导的活性氧（ROS）爆发。DH5α诱导的气孔关闭可在特定环境条件下被抑制或掩盖，例如低浓度二氧化碳（[CO₂]）、黑暗以及干旱等。对高湿度处理的蚕豆植株喷施高浓度脱落酸（ABA），可降低其气孔开度。与之一致的是，在高湿度条件下，外施脱落酸可缓解DH5α细菌在蚕豆叶片中的大量增殖。本研究数据表明，细菌在叶表面的成功定殖，与特定环境因子调控的气孔开度变化密切相关。