Transgenerational immune priming in plants

为了应对压力，植物和动物可以在生物学上表现出快速的变化，使它们能够最大限度地适应环境。暴露在压力下也会产生长期的免疫“记忆”，这使个体能够对未来的暴露做出更快、更强的防御反应。近年来，越来越多的证据表明，个体暴露于压力下也会影响其后代未来的压力反应。这种效应被称为“跨代效应”，并被认为是为了在可能遇到类似压力的后代中最大限度地提高个体基因库的存活率而进化的。我们最近有了一个重要的发现，患病植物的后代比基因相同的健康植物的后代更具抗性。这种增强的抵抗力持续了至少两代无压力的人，这表明是表观遗传。在没有病原体的情况下，抗性后代没有表现出增加的防御活性，而是表现出防御基因对感染的反应性增加。因此，我们将这种现象称为“跨代免疫启动”（TGIP），因为后代植物“启动”对感染的反应更快。重要的是，我们已经开始揭示支撑这种植物免疫记忆的机制，并发现TGIP是基于DNA甲基化的，这是一种可逆的DNA修饰，可以在不改变DNA序列的情况下对基因活性产生深远影响。跨代免疫反应对自然植物种群具有重要意义，并为可持续农业的开发提供了机会。通过表观遗传操作提高对病虫害的抵抗力的能力提供了一种新的机制，通过这种机制可以减少对化学品的依赖，而不必改变我们优良作物品种的基因组成。在本项目中，我们将探讨TGIP的生物学意义及其分子机制。首先，我们将研究TGIP是否可以在只有母系植物经历疾病胁迫时建立，或者父系组织是否也可以传递启动信息。这将为了解TGIP是如何演变的及其建立的机制提供线索。除了衡量TGIP在增加后代抗逆性方面的好处外，我们还将确定在哪里存在权衡：当针对一种形式的压力启动时会对另一种形式的耐受性产生负面影响。因此，我们将采用不同形式的胁迫（疾病、草食、盐度）在不同的亲本系中诱导TGIP，然后测量其后代对每种不同胁迫的抗性程度。这些成本和收益最初将根据抗逆性表型进行测量，但为了加深理解，我们将进行后续检测，以测量一组已定义的应激反应标记基因的表达，并使用质谱法生成代谢物谱。最后，我们将在竞争中从启动种群中培养子代，以测试TGIP的总体生殖适应性效益。在这些现象学研究的同时，我们将利用下一代测序技术来确定TGIP建立和维持的机制。由于基因反应性的长期表观遗传变化与DNA甲基化有关，我们将分析对照和引物植物的全基因组DNA甲基化模式。因此，我们将确定与增强抗逆性相关的差异甲基化区域。我们有证据表明，某些形式的小RNA分子（sirna）已知调节DNA甲基化在建立TGIP中很重要。因此，我们还将分析对照和引物植物中的sirna，以确定差异表达的sirna与DNA甲基化模式之间的相关性。

In response to stress, plants and animals can exhibit rapid changes in their biology, enabling them to maximise their fitness. Exposure to stress can also generate long-term immunological 'memory', which enables the individual to develop faster and stronger defence responses to future exposures. Over recent years, evidence has accumulated that exposure of an individual to stress can also influence future stress responses in its offspring. Such effects are referred to as 'transgenerational', and are assumed to have evolved to maximise survival of an individual's gene pool in future generations, which are likely to encounter similar stresses.We recently made the important discovery that progeny from diseased plants are more resistant than genetically identical offspring from healthy plants. This increased resistance persisted over at least two stress-free generations, suggesting epigenetic inheritance. Resistant progeny did not show increased defence activity in the absence of pathogens, but instead exhibited an increased responsiveness of defence genes to infection. We therefore refer to this phenomenon as 'transgenerational immune priming' (TGIP), since progeny plants are 'primed' to respond more rapidly to infection. Importantly, we have begun to uncover the mechanisms underpinning this immunological plant memory, and discovered that TGIP is based on DNA methylation, a reversible DNA modification that can have a profound impact on gene activity without changes in DNA sequence.Transgenerational immune responses have important implications for natural plant populations, and present an opportunity for exploitation in sustainable agriculture. The ability to improve resistance to pests and diseases through epigenetic manipulation provides a new mechanism by which reliance on chemicals can be reduced without having to change the genetic make-up of our elite crop varieties.In this project, we will investigate the biological significance of TGIP and the molecular mechanisms behind it. Firstly, we will examine whether TGIP can be established when disease stress is experienced only by the maternal plant, or whether paternal tissues can also transmit priming information. This will provide clues as to how TGIP evolved and the mechanism by which it is established. As well as measuring the benefits of TGIP in terms of increased stress resistance in offspring, we will also identify where there are trade-offs: when priming against one form of stress has a negative impact on tolerance to another. Thus, we will employ different forms of stress (disease, herbivory, salinity) to induce TGIP in different parental lines, and then measure the degree of resistance to each of these different stresses in their progeny. These costs and benefits will be measured initially in terms of stress resistance phenotypes, but to add depth of understanding, we will follow up with assays to measure expression of a defined set of stress-responsive marker genes and use mass spectrometry to generate metabolite profiles. Finally, we will grow progeny lines from primed populations in competition to test for overall reproductive fitness benefits for TGIP.In parallel with these phenomenological studies, we will exploit next-generation sequencing technologies to identify the mechanisms involved in the establishment and maintenance of TGIP. Since long-term epigenetic changes in gene responsiveness are associated with DNA methylation, we will profile genome-wide DNA methylation patterns in control and primed plants. Thus, we will identify differentially-methylated regions linked to enhanced stress resistance. We have evidence that certain forms of small RNA molecule (siRNAs) known to regulate DNA methylation are important in establishing TGIP. Therefore, we will also profile siRNAs in control and primed plants to identify correlations between differentially expressed siRNAs and DNA methylation patterns.