Transcriptome analysis of the symbiotic response of Arabidopsis at different temperatures.. Transcriptome analysis of the symbiotic response of Arabidopsis at different temperatures.

High ambient temperature regulated the plant systemic response to the beneficial endophytic fungus Serendipita indica. Most plants in nature establish symbiotic associations with endophytic fungi in soil. Beneficial endophytic fungi induce a systemic response in the aboveground parts of the host plant, thus promoting the growth and fitness of host plants. Meanwhile, temperature elevation from climate change widely affects global plant biodiversity as well as crop quality and yield. Over the past decades, great progresses have been made in the response of plants to high ambient temperature and to symbiosis with endophytic fungi. However, little is known about their synergistic effect on host plants. The endophytic fungus Serendipita indica colonizes the roots of a wide range of plants, including Arabidopsis. Based on the Arabidopsis-S. indica symbiosis experimental system, we analyzed the synergistic effect of high ambient temperature and endophytic fungal symbiosis on host plants. By transcriptome analysis, we found that DNA replication-related genes were significantly upregulated during the systemic response of Arabidopsis aboveground parts to S. indica colonization. Plant hormones, such as jasmonic acid (JA) and ethylene (ET), play important roles in plant growth and systemic responses. We found that high ambient temperature repressed the JA and ET signaling pathways of Arabidopsis aboveground parts during the systemic response to S. indica colonization in roots. Meanwhile, PIF4 is the central hub transcription factor controlling plant thermosensory growth under high ambient temperature in Arabidopsis. PIF4 is also involving JA and/or ET signaling pathway. We found that PIF4 target genes overlapped with many differentially expressed genes (DEGs) during the systemic response, and further showed that the growth promotion efficiency of S. indica on the pif4 mutant was higher than that on the wild type plants. Overall design: The aboveground parts of S. indica-inoculated Arabidopsis at 7 dpi were harvested for transcriptome. Arabidopsis was grown on half-strength MS medium with 1.2% sucrose (½MS). The seeds were stratified at 4°C for 3 days and then first grown at 22°C under short-day growth condition (12 h: 12 h, day: night photoperiod, 7000 LX light) in growth chambers. Serendipita indica (syn. Piriformospora indica, DSM11827) fungus were grown and conserved in PDA medium (200 g L-1 potato, 20 g L-1 dextrose and 20 g L-1 agar). For cocultivation with S. indica, 9-day-old Arabidopsis seedlings were inoculated with S. indica in PNM medium plates. S. indica-incubated (Si) and control (CK) samples were grown at 22°C, 25°C or 28°C under short-day growth condition.

环境高温调控植物对有益内生真菌印度梨形孢（Serendipita indica）的系统响应。自然环境中，多数植物会与土壤内生真菌建立共生关系。有益内生真菌可诱导宿主植物地上部分产生系统响应，进而促进宿主植物生长与适应性。与此同时，气候变化引发的温度升高广泛影响全球植物生物多样性，以及作物品质与产量。过去数十年间，学界在植物应对环境高温、以及与内生真菌共生的响应机制领域已取得诸多进展，但二者对宿主植物的协同效应仍鲜为人知。

内生真菌印度梨形孢可定殖于包括拟南芥（Arabidopsis）在内的多种植物根系。本研究基于拟南芥-印度梨形孢共生实验体系，分析了环境高温与内生真菌共生对宿主植物的协同效应。通过转录组（transcriptome）分析，我们发现拟南芥地上部分在应对根系印度梨形孢定殖的系统响应过程中，DNA复制相关基因显著上调表达。植物激素如茉莉酸（jasmonic acid, JA）与乙烯（ethylene, ET）在植物生长及系统响应中发挥关键作用。研究发现，在拟南芥地上部分应对根系印度梨形孢定殖的系统响应过程中，环境高温会抑制其茉莉酸与乙烯信号通路。光敏色素互作因子4（PIF4）是拟南芥中调控高温下植物温度感知生长的核心转录因子枢纽，同时也参与茉莉酸和/或乙烯信号通路。我们发现，系统响应过程中PIF4的靶基因与大量差异表达基因（differentially expressed genes, DEGs）存在重叠，并进一步证实印度梨形孢对pif4突变体的促生长效率高于其对野生型植株的促生长效率。

实验总体设计：于接种印度梨形孢后第7天（7 dpi）采集拟南芥地上部分用于转录组测序分析。拟南芥培养于添加1.2%蔗糖的1/2 MS培养基（half-strength MS medium, ½MS）中。种子先在4℃下低温层积3天，随后于22℃、短日照条件（光照12小时：黑暗12小时，光照强度7000 LX）的生长箱中初始培养。印度梨形孢（别名：梨形孢霉Piriformospora indica，菌株编号DSM11827）在PDA培养基（200 g·L⁻¹马铃薯提取物、20 g·L⁻¹葡萄糖、20 g·L⁻¹琼脂）中培养与保藏。与印度梨形孢共培养时，将9日龄拟南芥幼苗接种至PNM培养基平板上的印度梨形孢菌株中。接种印度梨形孢（Si组）与对照（CK组）的样品均在22℃、25℃或28℃的短日照条件下培养。