Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, Stavanger, Norway.
Plant Signal Behav. 2009 Nov;4(11):1084-6. doi: 10.4161/psb.4.11.9795. Epub 2009 Nov 12.
Light perceived by phytochromes will induce genes of nitrogen assimilation, however, transducing components in the signaling cascades to these genes are hardly known. Recently the bZIP transcription factors HY5 (LONG HYPOCOTYL5) and HYH (HOMOLOG OF HY5) were identified as positive regulators in light activation of NIA2 (nitrate reductase 2). The bHLH transcription factor PIF4 (PHYTOCHROME INTERACTING FACTOR 4) was revealed as an inhibitor of NIA2 expression. In contrast to NIA2, expression of other genes of nitrogen assimilation, NRT1.1 (dual-affinity nitrate transporter 1.1), NIA1 (nitrate reductase 1), NIR (nitrite reductase), GLN2 (glutamine synthetase 2) and GLU1 (glutamate synthase 1) were not promoted by HY5/HYH or inhibited by PIF4. NIA2 as the outstanding gene of nitrate assimilation regarding HY5/HYH and PIFs may have evolved in connection with the cytosolic leaf localization of nitrate reductase, and adverse effects of the products, nitrite, nitric oxide and active oxygen species formed by the enzyme.
光敏色素感知到的光会诱导氮同化基因的表达，然而，将信号级联中的转导成分传递到这些基因的机制还知之甚少。最近，bZIP 转录因子 HY5（长日下胚轴 5）和 HYH（HY5 的同源物）被鉴定为氮同化基因 NIA2（硝酸还原酶 2）光激活的正调控因子。bHLH 转录因子 PIF4（光形态建成相互作用因子 4）被揭示为 NIA2 表达的抑制剂。与 NIA2 不同，其他氮同化基因的表达，如 NRT1.1（双亲和硝酸转运体 1.1）、NIA1（硝酸还原酶 1）、NIR（亚硝酸盐还原酶）、GLN2（谷氨酰胺合酶 2）和 GLU1（谷氨酸合酶 1），不受 HY5/HYH 或 PIF4 的促进或抑制。NIA2 作为硝酸盐同化的突出基因，与 HY5/HYH 和 PIFs 有关，可能与硝酸还原酶在细胞质中的叶定位以及酶形成的亚硝酸盐、一氧化氮和活性氧等产物的不利影响有关。
