Biology Reference
In-Depth Information
Results
To determine directly the role of Arabidopsis WRKY2 transcription factor
during ABA-dependent seed germination and postgermination growth arrest,
we isolated T-DNA insertion mutants. Two independent T-DNA insertion
mutants for WRKY2 were hypersensitive to ABA responses only during seed
germination and postgermination early growth. wrky2 mutants displayed de-
layed or decreased expression of ABI5 and ABI3, but increased or prolonged
expression of Em1 and Em6. wrky2 mutants and wild type showed similar
levels of expression for miR159 and its target genes MYB33 and MYB101.
Analysis of WRKY2 expression level in ABA-insensitive and ABA-deficient
mutants abi5-1, abi3-1, aba2-3 and aba3-1 further indicated that ABA-in-
duced WRKY2 accumulation during germination and postgermination early
growth requires ABI5, ABI3, ABA2 and ABA3.
Conclusion
ABA hypersensitivity of the wrky2 mutants during seed germination and post-
germination early seedling establishment is attributable to elevated mRNA
levels of ABI5, ABI3 and ABI5-induced Em1 and Em6 in the mutants.
WRKY2-mediated ABA responses are independent of miR159 and its target
genes MYB33 and MYB101. ABI5, ABI3, ABA2 and ABA3 are important
regulators of the transcripts of WRKY2 by ABA treatment. Our results suggest
that WRKY2 transcription factor mediates seed germination and postgermi-
nation developmental arrest by ABA.
Background
Abscisic acid (ABA) is a phytohormone regulating plant responses to a variety of
environmental stress, particularly water deprivation, notably by regulating sto-
matal aperture [1-4]. It also plays an essential role in mediating the initiation and
maintenance of seed dormancy [5]. Late in seed maturation, the embryo develops
and enters a dormant state that is triggered by an increase in the ABA concentra-
tion. This leads to the cessation of cell division and activation of genes encod-
ing seed storage proteins and proteins required to establish desiccation tolerance
[6]. Exposure of seeds to ABA during germination leads to rapid but reversible
arrest in development. ABA-mediated postgermination arrest allows germinat-
ing seedlings to survive early water stress [5]. Based on ABA inhibition of seed
germination, mutants with altered ABA sensitivity have been identified. These
screens have led to the identification of several ABA-insensitive genes [7-13]. The
transcription factors ABI3 and ABI5 are known to be important regulators of
ABA-dependent growth arrest during germination [14,15]. ABI5, an ABA-insensitive
