RNA-Seq transcriptome analysis of reactive oxygen species gene network in Mizuna plants grown in long-term space flight

Space environment is suspected to generate reactive oxygen species (ROS) and induce oxidative stress in plants however little is known about the gene expression of ROS gene network in plants grown in long-term space flight. RNA-Seq was used to define the large-scale gene expression profiles of Mizuna harvested after 27 days cultivation in the international space station to understand the molecular response and adaptation to space environment.Results: Total reads of transcripts from the Mizuna grown in the international space station as well as on the ground by RNA-Seq using next generation sequencing technology showed 8,258 and 14,170 transcripts up- and down-regulated in the space-grown Mizuna respectively when compared with those from the ground-grown Mizuna. A total of 20 in 32 ROS oxidative marker genes were up-regulated including high expression of 4 hallmarks and preferentially expressed gene associated with ROS-scavenging genes was thioredoxin glutaredoxin and alternative oxidase genes. In the transcription factors of ROS gene network MEKK1-MKK4-MPK3 OXI1-MKK4-MPK3 and OXI1-MPK3 of MAP cascades induction of WRKY22 by MEKK1-MKK4-MPK3 cascade induction of WRKY25 and repression of ZAT7 by Zat12 were suggested. RbohD and RbohF genes were up-regulated preferentially in NADPH oxidase genes which produce ROS.Conclusions: Our large-scale transcriptome analysis demonstrated that the space environment induced oxidative stress and ROS gene network was activated in the space-grown Mizuna some of which were common genes up-regulated by abiotic and biotic stress and were preferentially up-regulated genes by the space environment even though Mizuna grew in the space as well as on the ground showing that plants could acclimate to the space environment by reprograming the expression of ROS gene network.

太空环境疑似产生活性氧物种（ROS）并诱导植物发生氧化应激，然而，关于长期太空飞行中种植的植物ROS基因网络的表达研究知之甚少。本研究利用RNA-Seq技术，对在国际空间站内种植27天后收获的芥末菜的基因表达谱进行了大规模分析，以探究植物对太空环境的分子响应和适应性。结果显示：与国际空间站内种植的芥末菜相比，地面种植的芥末菜通过RNA-Seq技术得到的转录本总读数分别为8,258和14,170，其中在太空种植的芥末菜中上调和下调的转录本分别有8,258和14,170个。在32个ROS氧化标记基因中，有20个基因上调，包括4个标志性基因的高表达，以及与ROS清除基因相关的优先表达基因——硫氧还蛋白 glutaredoxin 和交替氧化酶基因。在ROS基因网络的转录因子中，MEKK1-MKK4-MPK3、OXI1-MKK4-MPK3和OXI1-MPK3的MAP级联途径中，MEKK1-MKK4-MPK3级联诱导WRKY22，WRKY25的诱导以及ZAT7的抑制被Zat12所介导。在产生ROS的NADPH氧化酶基因中，RbohD和RbohF基因优先上调。结论：我们的大规模转录组分析表明，太空环境诱导了氧化应激，太空种植的芥末菜中的ROS基因网络被激活，其中一些基因在非生物和生物胁迫下普遍上调，而太空环境下的优先上调基因表明，植物可以通过重新编程ROS基因网络的表达来适应太空环境。