Ectopic Expression of ABSCISIC ACID 2/GLUCOSE INSENSITIVE 1 in Arabidopsis Promotes Seed Dormancy and Stress Tolerance

Abstract

Abscisic acid (ABA) is an important phytohormone that plays a critical role in seed development, dormancy, and stress tolerance. 9-cis-Epoxycarotenoid dioxygenase is the key enzyme controlling ABA biosynthesis and stress tolerance. In this study, we investigated the effect of ectopic expression of another ABA biosynthesis gene, ABA2 (or GLUCOSE INSENSITIVE 1 [GIN1]) encoding a short-chain dehydrogenase/reductase in Arabidopsis (Arabidopsis thaliana). We show that ABA2-overexpressing transgenic plants with elevated ABA levels exhibited seed germination delay and more tolerance to salinity than wild type when grown on agar plates and/or in soil. However, the germination delay was abolished in transgenic plants showing ABA levels over 2-fold higher than that of wild type grown on 250 mM NaCl. The data suggest that there are distinct mechanisms underlying ABA-mediated inhibition of seed germination under diverse stress. The ABA-deficient mutant aba2, with a shorter primary root, can be restored to normal root growth by exogenous application of ABA, whereas transgenic plants overexpressing ABA2 showed normal root growth. The data reflect that the basal levels of ABA are essential for maintaining normal primary root elongation. Furthermore, analysis of ABA2 promoter activity with ABA2Tb-glucuronidase transgenic plants revealed that the promoter activity was enhanced by multiple prolonged stresses, such as drought, salinity, cold, and flooding, but not by short-term stress treatments. Coincidently, prolonged drought stress treatment led to the up-regulation of ABA biosynthetic and sugar-related genes. Thus, the data support ABA2 as a late expression gene that might have a fine-tuning function in mediating ABA biosynthesis through primary metabolic changes in response to stress.

Abscisic Acid and LATERAL ROOT ORGAN DEFECTIVE/NUMEROUS INFECTIONS AND POLYPHENOLICS Modulate Root Elongation via Reactive Oxygen Species in Medicago truncatula

“…In well-watered plants, low ABA levels caused by mutations in ABA biosynthetic genes reduce root length, as do high levels of ABA caused by addition of the hormone to the growth medium (Sharp et al, 1994;Cheng et al, 2002;Lin et al, 2007), suggesting that under normal growth conditions there is an optimal ABA level for root elongation and that deviating above or below that level reduces the ability of the root to elongate. Root growth is driven by two interrelated processes: cell division and cell elongation.…”

AtGASA6 Serves as an Integrator of Gibberellin-, Abscisic Acid- and Glucose-Signaling during Seed Germination in Arabidopsis

“…ABI3, ABI4, and ABI5 are critical regulators of seed development and seed germination in the ABA signaling pathway (LopezMolina et al, 2001(LopezMolina et al, , 2002Piskurewicz et al, 2008), the DELLA protein RGL2 is an important regulator of seed germination in the GA signaling pathway (Lee et al, 2002;Tyler et al, 2004), and GLUCOSE INSENSITIVE1 (GIN1) and GIN2 both play important roles in Glc signaling and seed germination (Moore et al, 2003;Lin et al, 2007). After exposure to light for 10 h, germinating seeds were harvested for analysis.…”

The Putative E3 Ubiquitin Ligase ECERIFERUM9 Regulates Abscisic Acid Biosynthesis and Response during Seed Germination and Postgermination Growth in Arabidopsis

“…ABA2 encodes a short-chain alcohol dehydrogenase, which catalyzes the conversion of xanthoxin to abscisic aldehyde in the ABA biosynthesis pathway (González-Guzmán et al, 2002). Overexpression of ABA2 promotes seed dormancy (Lin et al, 2007), whereas its loss of function reduces seed ABA levels and seed dormancy (Nambara et al, 1998). Seeds of the wild type, cer9-2, aba2-1, and the cer9-2 aba2-1 double mutant were planted on culture medium containing increasing concentrations of ABA (Fig.…”