Biosynthesis of DHGA(12) and its roles in Arabidopsis seedling establishment

Seed germination and photoautotrophic establishment are controlled by the antagonistic activity of the phytohormones gibberellins (GAs) and abscisic acid (ABA). Here we show that Arabidopsis thaliana GAS2 (Gain of Function in ABA-modulated Seed Germination 2), a protein belonging to the Fe-dependent 2-oxoglutarate dioxygenase superfamily, catalyzes the stereospecific hydration of GA(12) to produce GA(12) 16, 17-dihydro-16α-ol (DHGA(12)). We show that DHGA(12), a C(20)-GA has an atypical structure compared to known active GAs but can bind to the GA receptor (GID1c). DHGA(12) can promote seed germination, hypocotyl elongation and cotyledon greening. Silencing and over-expression of GAS2 alters the ABA/GA ratio and sensitivity to ABA during seed germination and photoautotrophic establishment. Hence, we propose that GAS2 acts to modulate hormonal balance during early seedling development.