Abstract
Seed germination is a critical step in a plant's life cycle that allows successful propagation and is therefore strictly controlled by endogenous and environmental signals. However, the molecular mechanisms underlying germination control remain elusive. Here, we report that the Arabidopsis (Arabidopsis thaliana) glutamate receptor homolog3.5 (AtGLR3.5) is predominantly expressed in germinating seeds and increases cytosolic Ca2+ concentration that counteracts the effect of abscisic acid (ABA) to promote germination. Repression of AtGLR3.5 impairs cytosolic Ca2+ concentration elevation, significantly delays germination, and enhances ABA sensitivity in seeds, whereas overexpression of AtGLR3.5 results in earlier germination and reduced seed sensitivity to ABA. Furthermore, we show that Ca2+ suppresses the expression of ABSCISIC ACID INSENSITIVE4 (ABI4), a key transcription factor involved in ABA response in seeds, and that ABI4 plays a fundamental role in modulation of Ca2+-dependent germination. Taken together, our results provide molecular genetic evidence that AtGLR3.5-mediated Ca2+ influx stimulates seed germination by antagonizing the inhibitory effects of ABA through suppression of ABI4. These findings establish, to our knowledge, a new and pivotal role of the plant glutamate receptor homolog and Ca2+ signaling in germination control and uncover the orchestrated modulation of the AtGLR3.5-mediated Ca2+ signal and ABA signaling via ABI4 to fine-tune the crucial developmental process, germination, in Arabidopsis.
Highlights
Seed germination is a critical step in a plant’s life cycle that allows successful propagation and is strictly controlled by endogenous and environmental signals
We show that the AtGLR3.5-mediated Ca2+ signal antagonizes the effect of abscisic acid (ABA) in seeds through inhibiting the expression of ABI4 and that ABI4 plays a fundamental role in Ca2+ responses in germination
EGTA drastically reduced germination, to as low as 30% of the control at 10 mM (Fig. 1C; P, 0.001 at 5 and 10 mM). These data show that adequate external Ca2+ is required for seeds to germinate, which points to an important role of Ca2+ in the earliest phase of the plant life cycle
Summary
Seed germination is a critical step in a plant’s life cycle that allows successful propagation and is strictly controlled by endogenous and environmental signals. It indicates that external Ca2+ may activate AtGLR3.5 at the protein level, rather than up-regulation of the gene expression to promote seed germination (Supplemental Fig. S6).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
