Expression of the Arabidopsis Mutant abi1 Gene Alters Abscisic Acid Sensitivity, Stomatal Development, and Growth Morphology in Gray Poplars

Abstract

The consequences of altered abscisic acid (ABA) sensitivity in gray poplar (Populus 3 canescens [Ait.] Sm.) development were examined by ectopic expression of the Arabidopsis (Arabidopsis thaliana) mutant abi1 (for abscisic acid insensitive1) gene. The expression resulted in an ABA-insensitive phenotype revealed by a strong tendency of abi1 poplars to wilt, impaired responsiveness of their stomata to ABA, and an ABA-resistant bud outgrowth. These plants therefore required cultivation under very humid conditions to prevent drought stress symptoms. Morphological alterations became evident when comparing abi1 poplars with poplars expressing Arabidopsis nonmutant ABI1 or wild-type plants. abi1 poplars showed increased stomatal size, enhanced shoot growth, and retarded leaf and root development. The increased stomatal size and its reversion to the size of wild-type plants by exogenous ABA indicate a role for ABA in regulating stomatal development. Enhanced shoot growth and retarded leaf and root development support the hypothesis that ABA acts independently from drought stress as a negative regulator of growth in shoots and as a positive regulator of growth in leaves and roots. In shoots, we observed an interaction of ABA with ethylene: abi1 poplars exhibited elevated ethylene production, and the ethylene perception inhibitor Ag + antagonized the enhanced shoot growth. Thus, we provide evidence that ABA acts as negative regulator of shoot growth in nonstressed poplars by restricting ethylene production. Furthermore, we show that ABA has a role in regulating shoot branching by inhibiting lateral bud outgrowth.

A Co-Opted Hormonal Cascade Activates Dormant Adventitious Root Primordia upon Flooding in Solanum dulcamara

“…In rice, ABA treatment hampers flooding-induced AR emergence by preventing epidermal cell death (Steffens and Sauter, 2005), but it has not been reported whether ABA levels actually go down at the site of the preformed AR primordia and whether this is sufficient to mimic the flooding and ethylene responses. ABA also has a prominent role in dormancy initiation and maintenance in seeds and vegetative organ buds (Arend et al, 2009;Nambara et al, 2010;Reddy et al, 2013). Interestingly, a (transient) dormancy phenotype has been reported for LR primordia in Arabidopsis and is thought to occur in situations where LR emergence is not required (e.g.…”

The Protein Kinase SnRK2.6 Mediates the Regulation of Sucrose Metabolism and Plant Growth in Arabidopsis

“…Strikingly, while conferring ABA insensitivity, abi1 enhances the hyponastic response of Arabidopsis petiole (Benschop et al, 2007), which is characteristic of an enhanced ethylene response. Concertedly, when expressed in gray poplar (Populus 3 canescens), abi1 elevated ethylene production (Arend et al, 2009). Likewise, ethylene can induce the expression of ABI1 (Benschop et al, 2007).…”

Abscisic Acid Is a General Negative Regulator of Arabidopsis Axillary Bud Growth

“…Exogenous ABA inhibited bud growth in pea (Arney and Mitchell, 1969), Arabidopsis (Chatfield et al, 2000), Ipomoea nil (Cline and Oh, 2006), and tomato (Solanum lycopersicum; Cline and Oh, 2006), while the carotenoid (and ABA) biosynthesis inhibitor fluridone promoted bud growth in Rosa hybrida (Le Bris et al, 1999). Isolated poplar (Populus 3 canescens) explants with transgenically reduced ABA sensitivity exhibited increased lateral bud growth (Arend et al, 2009), and transcriptome studies of branch development in Arabidopsis (González-Grandío et al, 2013) and sugarcane (Saccharum officinarum; Ortiz-Morea et al, 2013) provided additional support for an association of ABA with the process. Definitive proof for the function of ABA in regulating Arabidopsis axillary bud outgrowth responses to the R:FR was demonstrated using a combination of transcriptomic, biochemical, and genetic approaches (Reddy et al, 2013).…”