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 germination Root growth

Ler wild type

abi1 mutant

abi mutantwild type

Under drought stress condition

Water stress

Increase in ABA levels

CADPR IP3

Ca2+ 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-galFig 2

Structural Analysis of the AREB cDNAs AREB1aAREB2a

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