Abstract
The ERA (E. coli 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 Antirrhinum majus. However, the mechanism that regulates seed development remains unclear. Blasting the genome sequence revealed two homologies of ERG, AtERG1, and AtERG2 in Arabidopsis. In this study, we found that AtERG2 is localized in the mitochondria and binds mitochondrial 18S RNA. Promoter and transcript analyses indicated that AtERG2 was mainly expressed in the leaf vein, trichome, and ovule. The T-DNA insertion lines of AtERG2 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 aterg2-1 +/−. 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, and AOX1a, was up-regulated in the aterg2-1 +/− arrested seeds at 1.5 and 2.0 DAP, but not in wild-type (WT) and aterg2-1 +/− developed seeds. The cell death-related gene BAG6 was also transcriptionally activated in aterg2-1 +/− seeds arrested at 2.0 DAP. Additionally, the protein level of mitochondria protein ATPase Subunit 6 was lower in 2-DAP siliques of aterg2-1 +/− 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 in Arabidopsis.
Highlights
The small GTP-binding proteins (GTPases) are found in all domains of life and act as molecular switches that are “activated” by GTP and “inactivated” by the hydrolysis of GTP to GDP to regulate numerous cellular processes, such as signal transduction, reorganization of the cellular cytoskeleton, regulation of transcription and translation, protein transport and vesicle traffickingAtERG2 Essential for Embryo Development (Takai et al, 2001; Vernoud et al, 2003; Shan, 2016)
Previous studies showed that embryo development is dominantly affected by both the female gametophyte and the sporophytic tissue of the parent plant, which is regulated by two classes of maternal effect genes: the sporophytic maternal effects (SME) genes, which are required in the maternal sporophyte for proper embryo development, and the gametophytic maternal effect (GME) genes, which are required in the female gametophyte for proper embryo development (Grossniklaus et al, 1998; Evans and Kermicle, 2001; Pien and Grossniklaus, 2007)
We found that AtERG2 is a nucleus-encoded and mitochondria-localized E. coli Ras-like protein (ERA)-like GTPase in Arabidopsis, and the T-DNA insertion hemizygous plants of AtERG2 show a SME phenotype after self-crossing or back-crossing with WT, which suggested that aterg2 +/− represents a distinct class of mutants affecting seed development
Summary
The small GTP-binding proteins (GTPases) are found in all domains of life and act as molecular switches that are “activated” by GTP and “inactivated” by the hydrolysis of GTP to GDP to regulate numerous cellular processes, such as signal transduction, reorganization of the cellular cytoskeleton, regulation of transcription and translation, protein transport and vesicle traffickingAtERG2 Essential for Embryo Development (Takai et al, 2001; Vernoud et al, 2003; Shan, 2016). The small GTP-binding proteins (GTPases) are found in all domains of life and act as molecular switches that are “activated” by GTP and “inactivated” by the hydrolysis of GTP to GDP to regulate numerous cellular processes, such as signal transduction, reorganization of the cellular cytoskeleton, regulation of transcription and translation, protein transport and vesicle trafficking. The TRAFAC class includes proteins involved in translation, signal transduction (in particular, the extended Ras-like family), and cell motility. Tu et al showed that the GTPbinding form of ERA is helpful for recognition and binding to the (1530)GAUCACCUCC(1539) sequence at the 3′ end of 16S rRNA, and RNA recognition stimulates its GTP-hydrolysing activity and the switch to the GDP-binding form; the latter suggested that ERA acts as a chaperone for the processing and maturation of 16S rRNA to benefit the assembly of the 30S ribosomal subunit (Tu et al, 2009, 2011)
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