Growth attenuation under saline stress is mediated by the heterotrimeric G protein complex.

BACKGROUND: Plant growth is plastic, able to rapidly adjust to fluctuation in environmental conditions such as drought and salinity. Due to long-term irrigation use in agricultural systems, soil salinity is increasing; consequently crop yield is adversely affected. It is known that salt tolerance is a quantitative trait supported by genes affecting ion homeostasis, ion transport, ion compartmentalization and ion selectivity. Less is known about pathways connecting NaCl and cell proliferation and cell death. Plant growth and cell proliferation is, in part, controlled by the concerted activity of the heterotrimeric G-protein complex with glucose. Prompted by the abundance of stress-related, functional annotations of genes encoding proteins that interact with core components of the Arabidopsis heterotrimeric G protein complex (AtRGS1, AtGPA1, AGB1, and AGG), we tested the hypothesis that G proteins modulate plant growth under salt stress. RESULTS: Na+ activates G signaling as quantitated by internalization of Arabidopsis Regulator of G Signaling protein 1 (AtRGS1). Despite being components of a singular signaling complex loss of the Gß subunit (agb1-2 mutant) conferred accelerated senescence and aborted development in the presence of Na+, whereas loss of AtRGS1 (rgs1-2 mutant) conferred Na+ tolerance evident as less attenuated shoot growth and senescence. Site-directed changes in the Gα and Gßγ protein-protein interface were made to disrupt the interaction between the Gα and Gßγ subunits in order to elevate free activated Gα subunit and free Gßγ dimer at the plasma membrane. These mutations conferred sodium tolerance. Glucose in the growth media improved the survival under salt stress in Col but not in agb1-2 or rgs1-2 mutants. CONCLUSIONS: These results demonstrate a direct role for G-protein signaling in the plant growth response to salt stress. The contrasting phenotypes of agb1-2 and rgs1-2 mutants suggest that G-proteins balance growth and death under salt stress. The phenotypes of the loss-of-function mutations prompted the model that during salt stress, G activation promotes growth and attenuates senescence probably by releasing ER stress.

The wiring diagram for plant G signaling.

Like electronic circuits, the modular arrangement of cell-signaling networks decides how inputs produce outputs. Animal heterotrimeric guanine nucleotide binding proteins (G-proteins) operate as switches in the circuits that signal between extracellular agonists and intracellular effectors. There still is no biochemical evidence for a receptor or its agonist in the plant G-protein pathways. Plant G-proteins deviate in many important ways from the animal paradigm. This review covers important discoveries from the last two years that enlighten these differences and ends describing alternative wiring diagrams for the plant signaling circuits regulated by G-proteins. We propose that plant G-proteins are integrated in the signaling circuits as variable resistor rather than switches, controlling the flux of information in response to the cell's metabolic state.

Genome-wide quantitative identification of DNA differentially methylated sites in Arabidopsis seedlings growing at different water potential.

BACKGROUND: In eukaryotes, the combinatorial usage of cis-regulatory elements enables the assembly of composite genetic switches to integrate multifarious, convergent signals within a single promoter. Plants as sessile organisms, incapable of seeking for optimal conditions, rely on the use of this resource to adapt to changing environments. Emerging evidence suggests that the transcriptional responses of plants to stress are associated with epigenetic processes that govern chromatin accessibility. However, the extent at which specific chromatin modifications contribute to gene regulation has not been assessed. METHODOLOGY/PRINCIPAL FINDINGS: In the present work, we combined methyl-sensitive-cut counting and RNA-seq to follow the transcriptional and epigenetic response of plants to simulated drought. Comprehensive genome wide evidence supports the notion that the methylome is widely reactive to water potential. The predominant changes in methylomes were loci in the promoters of genes encoding for proteins suited to cope with the environmental challenge. CONCLUSION/SIGNIFICANCE: These selective changes in the methylome with corresponding changes in gene transcription suggest drought sets in motion an instructive mechanism guiding epigenetic machinery toward specific effectors genes.