Poster: Hormone synthesis & metabolism

Abs # 476: Ectopic expression of ABA2/GIN1 in Arabidopsis promotes primary root elongation and salinity tolerance

Presenter:	Cheng, Wan-Hsing
Authors	Lin, Pei-Chi  (A)   Hwang, San-Gwang  (A)   Sheen, Jen  (B)   Cheng, Wan-Hsing  (A)
Affiliations:	(A): Institute of Botany, Academia Sinica, Taipei, Taiwan, R.O.C. (B): Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massa. General Hospital, Boston, MA 02114, U.S.A.

Abscisic acid (ABA) is one of the most important phytohormones, which plays a critical role in plant growth and development through a wide range of gene regulation. ABA2 (or GLUCOSE INSENSITIVE1, GIN1) encodes a short-chain dehydrogenase/reductase (SDR1) involved in ABA biosynthesis pathway. The enzyme catalyzes the multiple-step conversion of xanthoxin to abscisic aldehyde in the cytosol. In this study, we demonstrate that primary root elongation was promoted in ABA2 over-expression transgenic plants with ~60 fold higher ABA2 transcript than that of wild type in liquid culture; the enhanced root growth was further confirmed by the exogenous ABA (<100 nM), but blocked by floridone (1£gM), an ABA inhibitor. The over-expression transgenic lines also revealed seed germination delay on low (2% Glc) or high (6% Glc) sugar concentration relative to wild type, presumably due to ABA accumulation. However, the transgenic lines at high NaCl concentration (250 mM) germinated earlier than wild type, indicating that there are distinct mechanisms underlying ABA-regulated seed germination under diverse stresses. Furthermore, ABA2 promoter activity assay using ABA2::GUS transgenic plants indicated that the promoter activity was enhanced by stresses, including drought, salinity, cold and flooding. Bioassay further confirmed that the over-expression transgenic plants were phenotypically more resistant to salinity than wild type when grown on agar plate or soil. Our results suggest that in addition to enhancing seed dormancy, transgenic plants over-expressing ABA2 promote primary root elongation and salt tolerance.