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

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

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00182

DOI=10.3389/fpls.2018.00182

ISSN=1664-462X

ABSTRACT=<p>The ERA (<italic>E. coli</italic> RAS-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 in <italic>Antirrhinum majus</italic>. However, the mechanism that regulates seed development remains unclear. Blasting the genome sequence revealed two homologies of ERG, AtERG1, and AtERG2 in <italic>Arabidopsis</italic>. In this study, we found that AtERG2 is localized in the mitochondria and binds mitochondrial 18S RNA. Promoter and transcript analyses indicated that <italic>AtERG2</italic> was mainly expressed in the leaf vein, trichome, and ovule. The T-DNA insertion lines of <italic>AtERG2</italic> showed 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 in <italic>aterg2-1</italic> +<italic>/</italic>−. 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, <italic>WRKY40, ANAC017</italic>, and <italic>AOX1a</italic>, was up-regulated in the <italic>aterg2-1</italic> +<italic>/</italic>− arrested seeds at 1.5 and 2.0 DAP, but not in wild-type (WT) and <italic>aterg2-1</italic> +<italic>/</italic>− developed seeds. The cell death-related gene <italic>BAG6</italic> was also transcriptionally activated in <italic>aterg2-1</italic> +<italic>/</italic>− seeds arrested at 2.0 DAP. Additionally, the protein level of mitochondria protein ATPase Subunit 6 was lower in 2-DAP siliques of <italic>aterg2-1</italic> +<italic>/</italic>− 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 in <italic>Arabidopsis</italic>.</p>