The Laboratory of Plant Nutrition and Fertilizers, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 1138657 Japan.
RIKEN Center for Sustainable Resource Science, Kanagawa, 2300045 Japan.
Plant Cell Physiol. 2021 Oct 29;62(7):1156-1167. doi: 10.1093/pcp/pcab035.
Nitrate is an important nutrient and signaling molecule in plants, which modulates the expression of many genes and regulates plant growth. In paddy-grown rice (Oryza sativa), nitrogen is mostly supplied in the form of ammonium but can also be supplied in the form of nitrate. Several nitrogen transporters and nitrate assimilation enzymes have been identified and functionally characterized in rice. However, little is known regarding the nitrate sensing system in rice, and the regulatory mechanisms of nitrate-related genes remain to be elucidated. In recent years, NIN-like proteins (NLPs) have been described as key transcription factors of nitrogen responses in Arabidopsis thaliana, which implies that OsNLP4 is involved in the regulation of nitrate assimilation and nitrogen use efficiency in rice. Here, we show that OsNLP4 can influence plant growth by affecting nitrate reductase (NR) activity. The growth of OsNLP4 knockdown mutants was reduced when nitrate was supplied, but not when ammonium was supplied. The nitrate concentration was significantly reduced in osnlp4 mutants. Furthermore, the concentrations of iron and molybdenum, essential elements for NR activity, were reduced in OsNLP4 knockdown mutants. We propose that, in addition to the regulation of gene expression within the nitrate signaling pathway, OsNLP4 can affect the NR activity and nitrate-dependent growth of rice. Our results support a working model for the role of OsNLP4 in the nitrate signaling pathway.
硝酸盐是植物中重要的营养物质和信号分子，调节许多基因的表达，调控植物生长。在稻田生长的水稻（Oryza sativa）中，氮主要以铵的形式供应，但也可以以硝酸盐的形式供应。已经在水稻中鉴定和功能表征了几种氮转运体和硝酸盐同化酶。然而，关于水稻中硝酸盐感应系统知之甚少，硝酸盐相关基因的调控机制仍有待阐明。近年来，NIN 样蛋白（NLPs）被描述为拟南芥氮响应的关键转录因子，这意味着 OsNLP4 参与了水稻中硝酸盐同化和氮利用效率的调节。在这里，我们表明 OsNLP4 可以通过影响硝酸还原酶（NR）活性来影响植物生长。当供应硝酸盐时，OsNLP4 敲低突变体的生长受到抑制，但当供应铵时则不受抑制。在 osnlp4 突变体中硝酸盐浓度显著降低。此外，NR 活性必需元素铁和钼的浓度在 OsNLP4 敲低突变体中降低。我们提出，除了在硝酸盐信号通路中调节基因表达外，OsNLP4 还可以影响水稻的 NR 活性和硝酸盐依赖性生长。我们的结果支持了 OsNLP4 在硝酸盐信号通路中的作用模型。
