外源褪黑素促进干旱胁迫下春大豆苗期侧根发育及调控根系发育的抗性机理研究

The growth of lateral roots can enhance the absorption ability of plant roots to water and mineral nutrients with reacting first to drought stress. Melatonin is a natural antioxidant that not only promotes the growth of plant roots but also improves plant resistance to adversity stress. However, little is known about the mechanism of exogenous melatonin on the promoting of drought stress with lateral root initiation and regulation of root system development at spring soybean seeding. In order to clarify the mechanism of exogenous melatonin on the promoting of drought stress with lateral root initiation, experiments will be carried out using pot experiment in dry shed and seed germination test system in laboratory with drought sensitive and insensitive soybean varieties, drought stress treatments will be set up. The main techniques used include seedling phenotypic indexes, endogenous hormones, antioxidant enzymes activities, RNA-Seq high-throughput sequencing analysis. Base on the results, we can identify the regulation of relative physiological indexes under drought stress, analyze the mechanism of melatonin in promoting the growth of lateral root growth with seed germination and early seedling growth under drought stress. At the end reveal the mechanisms of exogenous melatonin on the promoting of drought stress with lateral root initiation. This study can help understanding the mechanism of exogenous melatonin improve soybean resistance to drought stress and provide scientific bases for the application of melatonin in practice.

侧根的发生可以增强植物根系对水分和矿质营养的吸收能力，在受到干旱胁迫时首先做出反应。褪黑素（Melatonin）是一种天然抗氧化剂，不仅促进植物体根系的建成还能增强其对逆境胁迫的抵御能力，然而关于干旱胁迫下外源褪黑素对春大豆侧根发育及调控根系发育的内在机理所知甚少。本项目利用旱棚盆栽和室内籽粒萌发试验系统，采用干旱敏感和不敏感型大豆品种，设置干旱胁迫处理，并结合幼苗表型指标测定、内源激素的变化、抗氧化酶活性分析、RNA-Seq高通量测序等关键技术和手段，明确褪黑素对干旱胁迫下大豆侧根相关生理指标的变化规律，解析籽粒萌发和幼苗生长感知干旱信号后测根的促生机理，并最终揭示外源褪黑素促进大豆苗期侧根发育的内在机制。本研究在理论上有助于深入理解外源褪黑素提高大豆干旱抗性机制，在实践上为褪黑素应用提供科学依据。

春旱是制约黑龙江省大豆生产的主要限制因素之一，褪黑素作为植物生长调节激素参与作物应对逆境胁迫的代谢过程。因此，研究外源褪黑素缓解干旱胁迫对大豆侧根发育具有重要意义。本研究在多年干旱胁迫研究的基础上，通过室内萌发和旱棚培养试验，研究了外源褪黑素对干旱条件下大豆侧根发育、引发区表型、内源激素含量的影响，筛选及鉴定了侧根引发区合成代谢相关基因，获得了与大豆干旱及抗旱性相关的差异表达基因和差异代谢产物，阐明了干旱胁迫条件下外源褪黑素促进大豆侧根发育的内在机制，为大豆抗旱性研究及褪黑素在大豆生产中的应用提供一定理论基础。（1）褪黑素浸种显著提高干旱胁迫下大豆种子发芽势，促进侧根引发区发育，激活了大豆体内抗氧化酶活性，清除过量的ROS，降低侧根引发区细胞膜脂损伤，提高大豆体内渗透调节物质含量，缓解由干旱胁迫导致细胞渗透压失衡所带来的损伤；通过转录组和代谢组学的联合分析，发现褪黑素浸种提高籽粒萌发过程中抗旱响应差异表达基因和差异代谢物主要表现在苯丙胺类生物合成代谢通路中。褪黑素浸种显著提高大豆V1和V3期干旱胁迫下侧根的抗氧化能力，调节根系内源激素变化，维持植物体内的渗透平衡，保障大豆正常的生长发育，单株粒重明显提高。（2）外源喷施褪黑素提高了干旱胁迫下抗氧化酶活性和非酶类抗氧化剂含量，维持氧化代谢和渗透压平衡，提高了大豆产量。富集分析明确了大豆响应干旱胁迫过程主要表现在侧根分生组织生长调控和生长素信号通路中，获得干旱胁迫下褪黑素调控的差异表达基因157个，明确了褪黑素诱导大豆侧根分生组织产生抗旱响应途径，主要表现在调控苯丙胺类生物合成代谢过程，定位在植物激素信号通路中色氨酸代谢途径，与防御机制（cytochrome P450 78A3）、信号转导机制（probable serine/threonine-protein kinase WNK5和serine/threonine-protein kinase AtPK2/AtPK19）、脂转运和代谢（tropinone reductase homolog At5g06060）、过氧化物酶（peroxidase 3、P7、12、46）等有关的酶和蛋白在表达中显著上调，为下一步研究褪黑素抗旱机制及抗旱功能基因分析奠定基础。