生长素及TOR信号途径在低氮刺激玉米根伸长中的调节机制

One strategy for maize to adapt low-nitrogen stress is to speed up root elongation so as to explore a larger soil space and increase N acquisition efficiency. The physiological mechanism underlying this response remains unclear. We hypothesize that the response of root elongation to low-N stress is regulated synchronously by auxin pathway (acid growth theory) and TOR pathway. Using two maize inbred lines (478 and W312) which root elongation has contrasting response to low-N stress, this study aims to the role of auxin pathway and TOR pathway in regulating root elongation in response to low-N stress. The experiments will be conducted under normal and low-N stress conditions. Exogenous chemicals affecting auxin or TOR pathway will be applied. The sucrose transporter mutant SUT1 as well as auxin reporter DR5::RFP line will also be used. The following parameters related to root elongation will be investigated: root growth kinematics, cell division and elongation, carbon and nitrogen metabolism, auxin level, proton exudation, expresson of genes encoding expansins, auxin transporter, TOR kinases etc. RNA-sequence analysis will be used to find the relationship between genes related to auxin and/or TOR pathway genes, cell division and elongation, and root elongation.

玉米适应低氮胁迫的策略之一是促进根的伸长、扩大土壤氮素空间有效性，进而提高氮素获助效率。迄今为止，有关低氮促进玉米根伸长的生理机制，仍然了解甚少。在前期工作基础上，本研究提出假说，玉米根系对低氮信号的响应可能受“雷帕霉素靶蛋白（TOR）途径”与生长素信号途径的协同调节。本研究拟利用本课题组前期工作鉴定出的、根伸长对低氮反应有显著差异的玉米自交系478与Wu312，在正常与低氮处理环境下，设置与生长素途径、TOR途径相关的外源物质处理，并借助玉米蔗糖运输突变体(SUT1)、生长素及其转运蛋白报道基因株系（DR5rev::mRFPer，ZmPIN1a::ZmPIN1a:YFP），分析根伸长动态、细胞分裂与伸长、碳氮代谢、生长素水平、生长素转运蛋白基因表达、质子分泌、膨胀素及TOR激酶等相关基因表达，并应用RNA-Sequence分析，剖析生长素途径与TOR途径在低氮调节玉米根伸长的生理机制。

玉米适应低氮胁迫的一个重要适应性策略是促进根的伸长，扩大土壤氮素的空间有效性，进而提高氮素获助效率。然而到目前为止，有关低氮促进玉米根伸长的生理机制，国际上仍然了解甚少。本研究利用本课题组前期工作鉴定出的、根系伸长对低氮反应有显著差异的玉米自交系478与W312，剖析了生长素途径与TOR途径在低氮调节玉米根伸长中的作用机制，探究低氮诱导玉米根生长反应的遗传机制。研究发现：（1）确证低氮供应通过生长素途径刺激玉米根的伸长。低氮刺激生长素向地运输，增加根尖生长素含量，刺激质子分泌，促进质外体酸化，导致细胞伸长加快。阻断地上部向根的生长素向地运输后，低氮不能诱导玉米根的伸长。（2）TOR途径在生长素的下游，参与调控根的伸长。外源施用雷帕霉素靶蛋白（TOR）抑制剂可以消除低氮下根的伸长反应。用生长素运输抑制剂NPA处理后降低从地上部到根的生长素转运时，TOR激酶的含量和TOR途径相关基因的表达量显著下降。（3）激素互作参与调控根系伸长。低氮上调了生长素、赤霉素、油菜素内酯合成基因表达，下调了细胞分裂素、乙烯、脱落酸合成基因表达，这种反应与基因型差异表现一致。（4）鉴定出34个控制根系及地上部性状的SNP位点和5个候选基因。发现来自SS亚群的玉米自交系对低氮反应强烈，对于耐低氮育种可能非常重要。