丛枝菌根真菌（AMF）调控干热河谷木棉磷代谢及其与抗旱性关系

The stony desertification of dry-hot valley in Southwest China is severe. Bambax ceiba L., a representational tree growing in dry-hot valley, has an excellent ability to survive there under distinct adverse conditions. However, its underlying adaptation mechanisms to such a low-phosphorus and dry-heat environmental conditions of dry-hot valley remain unclear. In this study, we will investigate the effects of Arbuscular mycorrhizal fungi (AMF) on water and phosphorus metabolism of B. ceiba under distinct water stress conditions, mainly focus on phosphorus metabolism in the "carbon-phosphorus exchange" of AMF symbiosis, with a variety of techniques, including whole genome sequencing, RNA-seq, rapid-amplification of cDNA ends (RACE), real-time quantitative PCR (qPCR), yeast mutant complementation and protein transient expression in tobacco. In addition, the response of AMF-induced and non-AMF-induced phosphate transporter genes to the phosphate uptake and redistribution of B. ceiba under different water stress conditions will be examined. This study will reveal the mechanisms of how AMF regulate phosphorus metabolism of B. ceiba and its resistance to drought. The results will provide theoretical foundation to accelarate the process of vegetation restoration of the fragile ecosystem in the dry-hot valley in Southwest China.

我国西南干热河谷地区土地石漠化严重。木棉（Bombax ceiba L.）作为干热河谷代表性树种，具有优良的逆境生存能力，然而其适应干热河谷特殊生境的机制尚不清楚。基于我国西南干热河谷地区干旱、土壤磷匮乏的环境现状，本研究拟通过分析不同程度水分胁迫下丛枝菌根真菌（Arbuscular mycorrhizal fungi, AMF）对干热河谷木棉水分代谢、磷代谢的影响，着重从丛枝菌根共生体“碳磷交换”的磷入手，采用基因组、转录组测序，RACE，实时荧光定量PCR，酵母突变体互补，烟草瞬时表达等技术和方法，系统研究水分胁迫下AMF诱导和非AMF诱导的磷酸盐转运蛋白基因的表达对干热河谷木棉磷吸收和再分配的响应。揭示AMF调控木棉的抗旱性及磷代谢作用机制，为提高植物环境适应能力，加速我国西南干热河谷地区脆弱生态系统植被恢复提供理论依据。

干旱是限制植物生长引起生态退化的主要非生物因素。本项目探究了干旱胁迫下丛枝菌根真菌（AMF）对干热河谷木棉光合、糖水平、水孔蛋白转录、磷代谢及活性氧代谢等方面的影响。结果表明水分胁迫或正常水分条件下AMF的定殖能够提高木棉Rubisco酶活性，上调Rubisco活化酶（RCA）基因表达，同时提高木棉光合速率、气孔导度、电子传递速率、最大光化学效率、降低CO2补偿点、提高水分利用效率。AMF定殖显著提高了干旱和非干旱处理下木棉的生物量。干旱胁迫下，AMF定殖提高了植株根部或/和叶部总可溶性糖、淀粉、海藻糖、山梨醇、葡萄糖和蔗糖的含量。转录分析发现正常水分处理AMF主要上调叶和根部水孔蛋白表达，水分胁迫下AMF主要下调叶部水孔蛋白表达。AMF定殖提高了干旱胁迫和正常水分条件下木棉磷素含量。鉴定的12条磷转运Ⅰ家族（PTⅠ）基因中有4条为AMF诱导表达成员，亚细胞定位表明除BcPT1.7定位在叶绿体外其余11条PTⅠ家族成员都定位在质膜。功能验证结果表明PT1.1、PT1.3、PT1.4和PT1.5具有磷酸盐转运功能。水分胁迫下，AMF定殖降低木棉丙二醛（MDA）和H2O2含量，降低超氧阴离子（O2·-）产生速率。AMF在干旱条件下主要下调了呼吸爆发氧化酶（Rboh）家族基因，而正常水分条件下AMF主要上调了Rboh家族基因。接种AMF增加了水分胁迫下木棉根部非酶类抗氧化物质含量和抗氧化酶活性。.总之，AMF定殖提高了干旱和非干旱条件下木棉的光和能力和生物量。AMF通过调控磷转运蛋白表达提高干旱和非干旱处理下木棉的磷素含量，同时调控水孔蛋白的表达提高水分利用效率，增加木棉糖类物质含量提高木棉的抗旱性。此外AMF调节Rboh的表达降低干旱胁迫下活性氧ROS的产生，提高ROS清除能力，缓解干旱诱导的ROS爆发，保持木棉植物ROS稳态，提高木棉抗旱能力。