Poster: Hormones

Abs # 617: Molecular phenotyping of Arabidopsis wild type and abi5 mutant during imbibition by microarray comprehensive expression analysis

Presenter:	Nakabayashi, Kazumi , kazumin@postman.riken.go.jp
Authors	Nakabayashi, Kazumi  (A)   Kamiya, Yuji  (A)   Nambara, Eiji  (A)
Affiliations:	(A): Plant Science Center, RIKEN (The Institute of Physical and Chemical Research)

Abscisic acid (ABA) plays a crucial role in seed maturation and dormancy. Recent studies identified several loci encoding transcription factors that are involved in ABA signaling in the seed. However, only fragmentary information has been reported on how the expression profiles differ in those mutants. Loss-of-function of ABI5 results in reduced ABA sensitivity in the seed and ABI5 is one of the bZip transcription factors that binds to ABRE (ABA responsive element). We have performed molecular characterization of WT and the abi5 mutant by microarray expression analysis. A statistical search for any cis-element in highly expressed genes in WT dry seed revealed one of the most typical ABRE that contains ACGT-core sequence. More detailed distribution analysis with the genes having 2-copy ABRE in the promoter showed an enhanced effect of the ABRE on high-level expression. Combinational analysis of ABRE with another cis-element CE (Coupling element) also showed a more apparent effect for high expression in dry seed. On the other hand, the correlation between high-level expression and ABRE diminished in imbibed seeds. This result is consistent with the endogenous ABA level that increases during seed maturation and dramatically decreases upon imbibition. In abi5 dry seed, the correlation between ABRE and high expression level is largely weakened. Furthermore, the same ABRE was identified from down-regulated genes in abi5 dry seed. These results indicate that the selected ABRE is one of the main elements that provides ABA inducibility during seed maturation, and ABI5 plays an important role on expression of those genes. In this way, microarray comprehensive analysis is useful for molecular phenotyping of the mutants verifying in vitro analysis in an in vivo situation.