We previously identified Arabidopsis genes homologous with the yeast ADA2 and GCN5 genes that encode components of the ADA and SAGA histone acetyltransferase complexes. In this report, we explore the biological roles of the Arabidopsis ADA2b and GCN5 genes. T-DNA insertion mutations in ADA2b and GCN5 were found to have pleiotropic effects on plant growth and development, including dwarf size, aberrant root development, and short petals and stamens in flowers. Approximately 5% of the 8200 genes assayed by DNA microarray analysis showed changes of expression in the mutants, three-fourths of which were upregulated and only half of which were altered similarly in the two mutant strains. In cold acclimation experiments, C-repeat binding factors (CBFs) were induced in the mutants as in wild-type plants, but subsequent transcription of cold-regulated ( COR ) genes was reduced in both mutants. Remarkably, nonacclimated ada2b-1 (but not gcn5-1 ) mutant plants were more freezing tolerant than nonacclimated wild-type plants, suggesting that ADA2b may directly or indirectly repress a freezing tolerance mechanism that does not require the expression of CBF or COR genes. We conclude that the Arabidopsis ADA2b and GCN5 proteins have both similar and distinct functions in plant growth, development, and gene expression and may be components of both a common coactivator complex and separate complexes with distinct biological activities.

The plant family Labiatae (Lamiaceae) is known for its fine medicinal and aromatic herbs like lavender, mint, oregano, sage and thyme and is a rich source of essential oils for the food, pharmaceutical and cosmetic industry. Besides its great economic importance, the Labiatae family contributes significantly to the endemic flora of Greece and Turkey. Owing to its economic and biological significance and to the difficult identification based on morphological characters of several of its taxa, the Labiatae family is an ideal case for developing DNA barcodes. The purpose of this study is to evaluate the utility of DNA barcoding on a local scale in discriminating Labiatae species in Chios Island (Greece) and the adjacent Çeşme-Karaburun Peninsula (Turkey). We chose three cpDNA regions (matK, rbcL, trnH-psbA) that were proposed by previous studies and tested them either as single region or as multiregion barcodes based on the criteria determined by Consortium for the Barcode of Life (CBOL). Our results show that matK and trnH-psbA taken as useful in discriminating species of the Labiatae, for the species we examined, as any multiregion combination. matK and trnH-psbA could serve as single-region barcodes for Labiatae species contributing to the conservation and the trade control of valuable plant resources.

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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.

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