Arabidopsis thaliana transcriptional co-activators ADA2b and SGF29a are implicated in salt stress responses

Abstract

The transcriptional co-activator ADA2b is a component of GCN5-containing complexes in eukaryotes. In Arabidopsis, ada2b mutants result in pleiotropic developmental defects and altered responses to low-temperature stress. SGF29 has recently been identified as another component of GCN5-containing complexes. In the Arabidopsis genome there are two orthologs of yeast SGF29, designated as SGF29a and SGF29b. We hypothesized that, in Arabidopsis, one or both SGF29 proteins may work in concert with ADA2b to regulate genes in response to abiotic stress, and we set out to explore the role of SGF29a and ADA2b in salt stress responses. In root growth and seed germination assays, sgf29a-1 mutants were more resistant to salt stress than their wild-type counterparts, whereas ada2b-1 mutant was hypersensitive. The sgf29a;ada2b double mutant displayed similar phenotypes to ada2b-1 mutant with reduced salt sensitivity. The expression of several abiotic stress-responsive genes was reduced in ada2b-1 mutants after 3 h of salt stress in comparison with sgf29a-1 and wild-type plants. In the sgf29a-1;ada2b-1 double mutant, the salt-induced gene expression was affected similarly to ada2b-1. These results suggest that under salt stress the function of SGF29a was masked by ADA2b and perhaps SGF29a could play an auxiliary role to ADA2b action. In chromatin immunoprecipitation assays, reduced levels of histone H3 and H4 acetylation in the promoter and coding region of COR6.6, RAB18, and RD29b genes were observed in ada2b-1 mutants relative to wild-type plants. In conclusion, ADA2b positively regulates salt-induced gene expression by maintaining the locus-specific acetylation of histones H4 and H3.

The role of transcriptional coactivator ADA2b in Arabidopsis abiotic stress responses

“…18 These results indicate that ADA2b may act as a positive regulator of salt-induced gene expression. This ADA2b's action is distinct from that of ADA2a and GCN5, since in the ada2a-2 and gcn5-1 as well as gcn5-2 mutants the expression of the stress-inducible genes was not affected by high salinity stress (Fig.…”

“…17 As a result in Arabidopsis, gcn5 mutants exhibit pleiotropic developmental defects, including dwarfism, loss of apical dominance, aberrant meristem function in root and shoot, leaf and flower development, short petals and stamens, flower infertility and plant responses to abiotic stress. 14,15,[17][18][19][20][21][22][23] Chromatin immunoprecipitation coupled with a promoter chip revealed that about 40% of the promoters are associated with the Arabidopsis GCN5 protein. 24 The GCN5 bromodomain is required for a small fraction (11%) of the AtGCN5 targets and their H3K14 acetylation.…”

“…Although at the moment there is no evidence of rapid stomata closure of ada2b-1 mutants in response to drought stress, those mutants were hypersensitive to ABA 20 a situation that could lead to rapid stomata closure. Moreover ada2b-1 mutants were hypersensitive to salt stress, 18,20 suggesting that ADA2b is not only involved in abiotic stress responses but also its function is stress-dependent. phenotypes.…”

“…34,35 GCN5 and ADA2b are involved in abiotic stress responses including low temperature and salt stress. 17,18,20 The CBF (C-repeat binding factor) family of transcriptional activators function as master regulators of cold acclimation in Arabidopsis by stimulating the transcription of cold-responsive (COR) genes. 36 COR root growth and seed germination assays, and in contrast to the ada2b salt responses, it was found that sgf29a mutants were more resistant to salt stress than their wild-type counterparts, suggesting that different components of HAT complexes may play a different role in plant abiotic stress responses.…”

Epigenetic Chromatin Regulators as Mediators of Abiotic Stress Responses in Cereals

“…A recent report showed that ADA2b positively regulates salt-induced gene expression by maintaining the locus-specific acetylation of histones H4 and H3b. ChIP assays demonstrated that the promoter and coding regions of COR6.6 (COLD RESPONSIVE 6.6), RAB18 (RESPONSIVE TO ABA 18), and RD29b genes had reduced levels of histone H3 and H4 acetylation in ada2b-1 mutants relative to wild-type plants [ 48 Kaldis et al, 2011]. Our group has identified HAT gene homologues from barley.…”