Heterotrimeric G protein signaling is important for cell-proliferative and glucose-sensing signal transduction pathways in the model plant organism Arabidopsis thaliana. AtRGS1 is a seven-transmembrane, RGS domain-containing protein that is a putative membrane receptor for D-glucose. Here we show, by using FRET, that D-glucose alters the interaction between the AtGPA1 and AtRGS1 in vivo. AtGPA1 is a unique heterotrimeric G protein ␣ subunit that is constitutively GTP-bound given its high spontaneous nucleotide exchange coupled with slow GTP hydrolysis. Analysis of a point mutation in AtRGS1 that abrogates GTPase-accelerating activity demonstrates that the regulation of AtGPA1 GTP hydrolysis mediates sugar signal transduction during Arabidopsis development, in contrast to animals where nucleotide exchange is the limiting step in the heterotrimeric G protein nucleotide cycle.D-glucose ͉ G protein-coupled receptor ͉ guanine nucleotide cycle ͉ RGS protein ͉ GTPase-accelerating protein
The performance of perovskite solar cells with inverted polarity (
p-i-n
) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of
p-i-n
perovskite-silicon tandem solar cells. A ~1 nm thick MgF
x
interlayer at the perovskite/C
60
interface through thermal evaporation favorably adjusts the surface energy of the perovskite layer, facilitating efficient electron extraction, and displaces C
60
from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion
V
oc
of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a ~1 cm
2
monolithic perovskite-silicon tandem solar cell. The tandem retained ~95% of its initial performance following damp-heat testing (85 Celsius at 85% relative humidity) for > 1000 hours.
Signaling through heterotrimeric G proteins is conserved in diverse eukaryotes. Compared to vertebrates, the simpler repertoire of G-protein complex and accessory components in Arabidopsis (Arabidopsis thaliana) offers a unique advantage over all other multicellular, genetic-model systems for dissecting the mechanism of G-protein signal transduction. One of several biological processes that the G-protein complex regulates in Arabidopsis is cell division. We determined cell production rate in the primary root and the formation of lateral roots in Arabidopsis to define individually the types of modulatory roles of the respective G-protein a-and b-subunits, as well as the heterotrimer in cell division. The growth rate of the root is in part a consequence of cell cycle maintenance in the root apical meristem (RAM), while lateral root production requires meristem formation by founder pericycle cells. Thus, a comparison of these two parameters in various genetic backgrounds enabled dissection of the role of the G-protein subunits in modulation of cell division, both in maintenance and initiation. Cell production rates were determined for the RAM and lateral root formation in gpa1 (Arabidopsis G-protein a-subunit) and agb1 (Arabidopsis G-protein b-subunit) single and double mutants, and in transgenic lines overexpressing GPA1 or AGB1 in agb1 or gpa1 mutant backgrounds, respectively. We found in the RAM that the heterotrimeric complex acts as an attenuator of cell proliferation, whereas the GTP-bound form of the Ga-subunit's role is a positive modulator. In contrast, for the formation of lateral roots, the Gbg-dimer acts largely independently of the Ga-subunit to attenuate cell division. These results suggest that Arabidopsis heterotrimeric G-protein subunits have differential and opposing roles in the modulation of cell division in roots.
SummaryAbscisic acid (ABA) is perceived by several different types of receptors in plant cells. At the cell surface, the ABA signal is proposed to be perceived by GCR2, which mediates ABA responses in seed germination, early seedling development and stomatal movement. GCR2 was also proposed to be a seven-transmembrane (7TM) G-protein-coupled receptor (GPCR). Here we characterize GCR2 and one of its two homologs, GCR2-LIKE 1 (GCL1), in ABA-mediated seed germination and early seedling development in Arabidopsis. We show that lossof-function mutations in GCL1 did not confer ABA insensitivity. Similarly, we did not observe ABA insensitivity in three independent gcr2 alleles. Furthermore, we generated gcr2 gcl1 double mutants and found that the double mutants still had near wild-type responses to ABA. Consistent with this, we found that the transcription of ABA marker genes was induced by ABA to levels that were comparable in wild type and gcr2 and gcl1 single and double mutants. On the other hand, the loss-of-function alleles of the sole Arabidopsis heterotrimeric G protein a subunit, GPA1, were hypersensitive to ABA in the ABA-inhibition of seed germination and early seedling development, disfavoring a genetic coupling of GCR2 by GPA1. Using multiple robust transmembrane prediction systems, GCR2 was predicted not to be a 7TM protein, a structural hallmark of GPCRs. Taken together, our results do not support the notion that GCR2 is an ABA-signaling GPCR in seed germination and early seedling development.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.