The ERA-Related GTPase AtERG2 Associated with Mitochondria 18S RNA Is Essential for Early Embryo Development in Arabidopsis

Pengyu Cheng, Hongjuan Li, Linlin Yuan, Huiyong Li, Lele Xi, Junjie Zhang, Jin Liu, Yingdian Wang, Heping Zhao, Huixin Zhao, Shengcheng Han

The ERA (E. coliRAS-like protein)-related GTPase (ERG) is a nuclear-encoded GTPase with two conserved domains: a GTPase domain and a K Homology (KH) domain. ERG plays a vital role in early seed development inAntirrhinum majus. However, the mechanism that regulates seed development remains unclear. Blasting the genome sequence revealed two homologies of ERG, AtERG1, and AtERG2 inArabidopsis. In this study, we found that AtERG2 is localized in the mitochondria and binds mitochondrial 18S RNA. Promoter and transcript analyses indicated thatAtERG2was mainly expressed in the leaf vein, trichome, and ovule. The T-DNA insertion lines ofAtERG2showed silique shortage, early seed abortion, and sporophytic maternal effects (SME), in which some seeds arrested in the zygotic stage at 1.5 days after pollination (DAP) and aborted at 2.0 DAP inaterg2-1+/-. We further showed that the ovules of these arrested seeds presented unusual tissue degradation inside the embryo sacs. Reactive oxygen species (ROS) accumulated at 1.0 and 1.5 DAP in the arrested seeds, and the transcription of several ROS-responsive genes,WRKY40, ANAC017, andAOX1a, was up-regulated in theaterg2-1+/- arrested seeds at 1.5 and 2.0 DAP, but not in wild-type (WT) andaterg2-1+/- developed seeds. The cell death-related geneBAG6was also transcriptionally activated inaterg2-1+/- seeds arrested at 2.0 DAP. Additionally, the protein level of mitochondria protein ATPase Subunit 6 was lower in 2-DAP siliques ofaterg2-1+/- than it was in those of WT. These results suggested that AtERG2 promotes early seed development by affecting the maturation of the mitochondria ribosome small subunit and mitochondrial protein translation inArabidopsis.