硝酸盐调控水稻种子休眠的分子机理研究

Pre-harvest sprouting which is resulted from reduced seed dormancy often leads to production loss of crops. Nitrate promotes plant growth and improves crop yield, but also reduces seed dormancy and thereby leads to pre-harvest sprouting. Thus, dissecting the molecular mechanism underlying nitrate regulated seed dormancy is critical not only for improving nitrogen use efficiency, but also for avoiding pre-harvest sprouting. By analyzing the germination rate of seeds cultured under high and low nitrogen condition, we found that nitrate promoted seed germination by reducing ABA content in rice seeds. Extensive screening of mutants involved in nitrate transportation, assimilation and signaling pathway, we identified the nitrate sensor NRT1.1B and NIN-like transcription factors NLP3/4 play important roles in regulating seed dormancy in rice. We also found that nitrate promotes the nuclear retention of NLP3 and NLP4 in rice protoplasts. Based on these results, here we would like to unveil the mechanism of the nitrate signaling components in regulating seed dormancy and provides theoretical basis for revealing the mechanism of nitrate regulated seed dormancy.

种子休眠程度过低而引起的穗发芽是导致作物减产的一个重要因素。氮肥的施用可显著促进植物生长，提高作物产量，但也在一定程度上降低了种子休眠程度，进而导致穗发芽。因此，解析氮调控水稻种子休眠的分子机理对于提高水稻氮利用效率，保证粮食高产稳产具有重要意义。不同氮条件下的萌发实验发现，硝酸盐能够抑制水稻种子的休眠过程。进一步研究发现，硝酸盐通过影响种子内ABA的含量来调控水稻种子休眠程度。有意思的是，硝酸盐信号通路中的关键组分NRT1.1B、NLP3/4参与了水稻种子休眠的调控。原生质体结果显示硝酸盐通过调控NLP3和NLP4的核质穿梭影响其功能。本项目拟在前期工作基础上，深入解析NRT1.1B和NLP3/4介导的硝酸盐信号调控种子休眠的分子机制，为解决生产实践中高肥条件导致种子休眠降低问题提供相关理论依据。

硝酸盐是植物获取氮源的主要形式，同时可以作为信号分子调控种子休眠和萌发。NRT1.1B是硝酸盐的transceptor，既负责硝酸盐的吸收和转运，又作为硝酸盐的感受器，感知硝酸盐信号。NLP3/4是硝酸盐信号通路中的核心转录因子，在介导硝酸盐信号转导过程中发挥重要的作用。本项目通过分析不同氮浓度对种子休眠的影响，发现氮能够抑制种子休眠，促进种子萌发。NRT1.1B和NLP3/4在介导硝酸盐调控水稻种子休眠的过程中发挥负调控作用，nrt1.1b和nlp3/4突变体种子休眠程度高。通过测定种子内ABA含量，发现氮素和NLP3/4对种子内ABA的合成发挥负调控作用。低氮条件下的种子和nlp3/4双突变体种子中总氮和硝态氮含量较低，说明NLP3/4通过影响植物对氮的吸收及氮向种子内的转运来介导硝酸盐对种子休眠的调控。这也为深入解析硝酸盐调控种子休眠的机制奠定基础。