Institute of Tropical Plant Sciences and Microbiology, National Cheng Kung University, Tainan, Taiwan.
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
Ann Bot. 2020 Jun 1;125(7):1091-1099. doi: 10.1093/aob/mcaa040.
Nitrate can stimulate seed germination of many plant species in the absence of light; however, the molecular mechanism of nitrate-promoted seed germination in the dark remains largely unclear and no component of this pathway has been identified yet. Here, we show that a plastid J-domain protein, DJC75/CRRJ, in arabidopsis (Arabidopsis thaliana) is important for nitrate-promoted seed germination in the dark.
The expression of DJC75 during imbibition in the dark was investigated. The seed germination rate of mutants defective in DJC75 was determined in the presence of nitrate when light cues for seed germination were eliminated by the treatment of imbibed seeds with a pulse of far-red light to inactivate phytochrome B (phyB), or by assaying germination in the dark with seeds harbouring the phyB mutation. The germination rates of mutants defective in CRRL, a J-like protein related to DJC75, and in two chloroplast Hsp70s were also measured in the presence of nitrate in darkness.
DJC75 was expressed during seed imbibition in the absence of light. Mutants defective in DJC75 showed seed germination defects in the presence of nitrate when light cues for seed germination were eliminated. Mutants defective in CRRL and in two chloroplast Hsp70s also exhibited similar seed germination defects. Upregulation of gibberellin biosynthetic gene GA3ox1 expression by nitrate in imbibed phyB mutant seeds was diminished when DJC75 was knocked out.
Our data suggest that plastid J-domain protein DJC75 regulates nitrate-promoted seed germination in the dark by upregulation of expression of the gibberellin biosynthetic gene GA3ox1 through an unknown mechanism and that DJC75 may work in concert with chloroplast Hsp70s to regulate nitrate-promoted seed germination. DJC75 is the first pathway component identified for nitrate-promoted seed germination in the dark.
硝酸盐在光照条件下可以刺激许多植物物种的种子萌发；然而，硝酸盐促进黑暗中种子萌发的分子机制在很大程度上仍不清楚，目前尚未鉴定出该途径的任何组成部分。在这里，我们表明拟南芥（Arabidopsis thaliana）中的质体 J 结构域蛋白 DJC75/CRRJ 对于硝酸盐在黑暗中促进种子萌发很重要。
研究了 DJC75 在黑暗中吸胀过程中的表达情况。当用远红光脉冲处理吸胀种子以灭活光敏色素 B（phyB）来消除种子萌发的光信号，或在黑暗中用含有 phyB 突变的种子进行萌发测定时，测定了 DJC75 缺陷突变体在硝酸盐存在下的种子萌发率。还测量了与 DJC75 相关的 J 样蛋白 CRRL 缺陷突变体以及两个叶绿体 Hsp70 缺陷突变体在黑暗中存在硝酸盐时的种子萌发率。
DJC75 在黑暗中种子吸胀过程中表达。当消除种子萌发的光信号时，Djc75 缺陷突变体在硝酸盐存在下表现出种子萌发缺陷。CRRL 缺陷突变体和两个叶绿体 Hsp70 缺陷突变体也表现出类似的种子萌发缺陷。在吸胀的 phyB 突变体种子中，硝酸盐上调 GA3ox1 基因的表达，而当敲除 DJC75 时，这种上调作用减弱。
我们的数据表明，质体 J 结构域蛋白 DJC75 通过未知机制通过上调 GA3ox1 基因的表达来调节黑暗中硝酸盐促进的种子萌发，而 DJC75 可能与叶绿体 Hsp70 一起协同作用来调节硝酸盐促进的种子萌发。Djc75 是鉴定出的第一个黑暗中硝酸盐促进种子萌发的途径组成部分。
