The Arabidopsis ABA‐INSENSITIVE (ABI) 4 factor acts as a central transcription activator of the expression of its own gene, and for the induction of ABI5 and SBE2.2 genes during sugar signaling

Abstract

SUMMARYThe transcription factor ABA INSENSITIVE 4 (ABI4), discovered nearly 10 years ago, plays a central role in a variety of functions in plants, including sugar responses. However, not until very recently has its mechanism of action begun to be elucidated. Modulating gene expression is one of the primary mechanisms of sugar regulation in plants. Nevertheless, the transcription factors involved in regulating sugar responses and their role(s) during the signal transduction cascade remain poorly defined. In this paper we analyzed the participation of ABI4, as it is one of the main transcription factors implicated in glucose signaling during early seedling development. Our studies show that ABI4 is an essential activator of its own expression during development, in ABA signaling and in sugar responses. It is also important for the glucose-mediated expression of the genes ABI5 and SBE2.2. We demonstrate that ABI4 binds directly to the promoter region of all three genes and activates their expression in vivo through at CE1-like element. Previous studies found that ABI4 also functions as a transcriptional repressor of sugar-regulated genes, therefore this transcription factor is a versatile protein with dual functions for modulating gene expression.

Expression of ABSCISIC ACID INSENSITIVE 4 ( ABI4 ) in developing Arabidopsis seedlings

“…16 It was argued that ABI4 expression is limited to seed maturation and to a few days following germination. 15,18,20 On the other hand, ABI4 was reported to be expressed in shoots and roots of three-week-old plants. 7 Furthermore, we recently showed, both quantitatively and histologically, that ABI4 is expressed in mature regions of the roots at later developmental stages and that its steady-state levels are enhanced by ABA and cytokinin and reduced by auxin.…”

“…At these stages, ABI4 was shown to be involved in glucose signaling, 12,14,16,17 sugar signaling and response pathways, 11,13,18 ABA signaling 3,[11][12][13]15 and lipid mobilization in the embryo and germinating seeds, 21,22 as well as in chloroplast functioning and retrograde signaling. 20,23 Other studies, using older plants, showed that ABI4 is involved in nitratemodulated root branching, 24 sugar insensitivity in fully expanded leaves, 25 responses to plant pathogens and tolerance to β-amino-butyric acid (BABA)-induced water stress, [26][27][28][29] mitochondrial retrograde signaling, 30 chloroplast photosynthesis, 31,32 and modulation of hormonal control of at this developmental stage.…”

“…In germinating seedlings, ABI4 was shown to be induced by external application of glucose [16][17][18][19] and mannitol 17 ABI4 was induced in ABA-treated imbibed seeds, 20 but not in germinating seedlings. 16 It was argued that ABI4 expression is limited to seed maturation and to a few days following germination.…”

MED18 interaction with distinct transcription factors regulates multiple plant functions

“…ABI4 is known to bind to the ABI5 promoter and enhance its expression 33 . This information prompted us to test whether MED18 directly interacts with ABI4 to regulate ABI5 gene expression.…”

ABI4 Activates DGAT1 Expression in Arabidopsis Seedlings during Nitrogen Deficiency

“…6C). GUS was expressed in the cotyledons, hypocotyls, and root tips of 60-50 7-d-old Col-0 seedlings, in accordance with the expression pattern of ABI4 (Bossi et al, 2009). On 0.1 mM N, GUS expression levels increased in cotyledons and hypocotyls.…”