丛枝菌根菌丝网络在番茄植株间传递干旱信号的机理

Drought is one of the most important environmental stresses that influence plant growth and development. Whether plants can perceive drought stress signal timely and effectively is vital for plant tolerance to drought stress. Previous findings from our team has demonstrated that common mycorrhizal networks (CMNs) widely existing in soils can function as a plant-plant underground communication channel where signals for disease resistance, anti-herbivore defense and induced defence can be transferred between the healthy and its neighbouring tomato plants facing biotic stress. However, it is unknown whether CMNs can transfer signals of abiotic environment stresses such as drought stress and trigger its tolerance responses. This study will address this issue. After CMN establishment between two tomato plants in pots with mycorrhizal fungus Funneliformis mosseae (syn. Glomus mosseae), a 'donor' plant will be treated with either drought, mannitol (simulated drought), or abscisic acid (ABA). Changes in stomatal conductance and pphotosynthetic rate, the activities of drought resistant enzymes and proteins, contents of soluble sugar, proline, ABA etc will be assayed in the drought free tomato plants with or without connection by CMNs with the drought-challenged plants. The induced expressions of drought resistant-related genes, and drought-related transcription factor genes will be determined using real-time qRT-PCR. Isotope-labelled signaling compounds (ABA) will be used to replace the drought treatment on 'donor' plants to trace potential signal transferred from 'donor' to 'reveiver' plants. This study is very important to reveal underground plant-plant communications, ecological functions of CMNs and mechanism of plant environmental stress perception and signal transfer between plants.

干旱是影响植物生长发育最主要的逆境胁迫之一。植物是否可以及时而有效地感知周围环境的干旱胁迫对植物及时启动干旱抵御机制至关重要。本课题组首次发现番茄可以通过在土壤中广泛存在的丛枝菌根菌丝网络（菌丝桥）在同种植株间传递抗病和抗虫信号。然而，菌根菌丝网络是否可以在植株间传递干旱等非生物环境胁迫的信号还缺乏研究。本项目拟利用摩西球囊霉在番茄植株间建立菌根菌丝桥后，将供体番茄进行干旱、聚乙二醇模拟干旱和脱落酸处理48小时后，然后检测受体番茄植株在没有干旱胁迫和有干旱胁迫两种情况下叶片气孔导度、光合速率、抗旱相关酶活性和蛋白、脯氨酸、可溶性糖、脱落酸等含量的变化，测定抗旱相关的反应基因、转录因子和信号转导途径关键基因表达的变化。通过使用带同位素的信号物质进行示踪，阐明番茄植株间通过菌丝桥传递的信号分子。研究对揭示植物间的地下通讯、菌根菌丝桥的生态学功能以及植物感知和传递环境胁迫信号机制均有重要意义。

干旱是影响植物生长发育最主要的逆境胁迫之一。植物是否可以及时而有效地感知周围环境的干旱胁迫对植物适应干旱胁迫至关重要。本课题率先发现番茄可以通过在土壤中广泛存在的丛枝菌根菌丝网络（菌丝桥）在同种植株间传递干旱非生物环境胁迫信号。本研究以番茄为材料，利用根内根生囊霉（Rhizophagus irregularis）在番茄植株间建立菌根菌丝桥后，对供体番茄进行干旱、喷施脱落酸处理，然后研究对受体番茄植株抗旱性与抗旱反应的影响。在供体番茄干旱胁迫处理下，有菌丝桥连接的受体番茄的气孔导度（gs）、胞间CO2浓度（Ci）、丙二醛含量（MDA）显著降低，植物水分利用效率（WUE）、叶片相对含水量、脯氨酸含量和根系ABA含量显著提高，根中独脚金内酯(SLs)合成关键基因SlCCD8表达量以及ABA合成途径基因SlAO和SlDXR显著上升。证明受体番茄通过菌丝桥感知到供体的干旱胁迫信号，进而关闭叶片气孔导致大气CO2（Ca）扩散至细胞间受阻，光合同化消耗了细胞间CO2，从而导致Ci降低。脱落酸（ABA）在植物应对干旱等非生物胁迫中发挥信号中枢的作用。ABA处理供体时，受体植株24 h 出现表现变化，气孔导度、胞间CO2浓度和蒸腾速率均显著下降。之后受体受到干旱时抗旱能力增强。这些结果表明，在供体受到干旱胁迫时，有菌丝桥连接的受体番茄能够感知供体的干旱胁迫信号，并做出一系列相应的胁迫响应：降低气孔开度，减少水分蒸腾耗散，提高光合水分利用率；激活独角金内酯激素信号途径促进根系生长；促进根ABA积累，下调水通道蛋白基因SlPIP2;1的表达，降低根系导水，减少水分流失等。随后在受体植株受到干旱胁迫时，受体变现出更好的抗旱适应性，包括更高的保护酶活性，高渗透调节物质的积累及更少的膜脂过氧化。本项目揭示了植物可以借助菌根菌丝网络在植物之间进行干旱信号传递的自然奥秘，由于该网络在土壤与植物群落中广泛存在，这使植物能够提前感知到周围环境在的干旱胁迫信号，促使植物提前做好抗旱准备，进而提高植物的抗旱能力。