Arabidopsis basic leucine zipper transcription factors involved in an abscisic acid-dependent signal transduction pathway under drought and high- salinity condition

ABA? - Phytohormone abscisic acid - ABA play important roles in vegetative tissues, seed maturation, dormancy to abiotic environmental stress such as drought, high salimity, cold -ABA promotes with ABI1, ABA2 stomatal closure in the guard cells and regulate the expression of many genes - ABA-inducible gene contain conserved ABRE Specific binding with bZIP protein - ABRE(ACGTGGC) in there promoter regions -Function as a cis-acting DNA element involved in ABA-regulated gene expression ABRE(ABA-responsive element)

-ABREs were first identified in the wheat Em gene ( seed during late embryogenesis), rice Rab16 gene (expressed in dehydrated vegetative tissues and maturating seed) -G-box (CACGTG) contein bZIP motif resembles the ABRE motif and functions in the regulation of plant genes in a variety of enviromental conditions (red light, UV light, anaerobiosis, wounding)

ABA Signal Pathway ABI (ABA-Insensitive)1, ABA2, ERA1 Encode protein phosphatase Key component of signal transduction in Arabidopsis regulate diverse response to the phytohormone abscisic acid Stomatal closure Seed dormancy Inhibition of regulation growth

abi1 : suppressors of non-germination GA-deficient lines phenotype : ABA deficient ; decreased stress or ABA induction of gene expression sugar-resistant seedling growth aba2 : Reduced dormancy phenotype : analogous to abi1 era1 : enhanced response to ABA at germination Expressed in vegetative tissues and are thought to be essential for negative regulation of ABA signaling during vegetative growth ABA-related Mutant

Ler wild type abi1 mutant Seedlig germinationRoot growth Ler wild type abi1 mutant

abi mutantwild type Under drought stress condition

Water stress Increase in ABA levels CADPR IP 3 Ca 2+ release from internal stores Phosphorylation and dephosphorylation events Gene induction ( ex : rd29b, Em, rd16) ABI1, ABA2

AREB1(ABA-Responsive element binding proteins), AREB2, AREB3 -AREB protein contained a sigle bZIP-type DNA-binding domain and up regulated by ABA Function of the AREB proteins in the ABA-dependent signaling pathway in vegetative tissues under dehydration stress condition

Identification of Cis-Acting Elements Involved in Dehydration- Responsive Expression of rd29b

Isolation of cDNAs Encoding DNA-Binding Proteins that Recognize ABRE in the 77-bp DNA Fragment of the rd29B Promoter Control 3-AT ß-gal Fig 2

Structural Analysis of the AREB cDNAs AREB1a AREB2a AREB2 bZIP

Expression of the AREB Genes Dry : 3 weeks NaCl : 250m ABA : 100µM Cold : 4°C

The AREB1 and AREB2 Proteins Transactivate the rd29B Promoter-GUS Fusion Gene in Leaf Protoplasts C: control N: NaCl 250mM 5h D: dehydrate 10h A: ABA 100 µM H: water 5h

Monomer in cultured T87 cell of Arabidopsis

ABA-Specific Phosphorylation of AREB1 and AREB2 Proteins 73G-131Q 84S-133D 335Y-401V Northen blot RT-PCR

-Induction of the dehydration-responsive Arabodpsis gene, rd29B, is mediated mainly ABA -Promoter of rd29B indicated that two ABREs are required for the dehydration- responsive expression of rd29B -Three cDNAs encoding bZIP type AREB1, 2, 3 were isolated by using the yeast one-hybrid system -AREB1,2 gene is up- regulated by drought, NaCl, ABA treatment in vegetative tissues -AREB1,2 proteins activated transcription by ABRE and required ABA for their activation, suppressed by protein kinase inhibitors -phosphorylation is necessary for their maximum activation by ABA, N-term rigion in the AREB proteins