BT2, a BTB Protein, Mediates Multiple Responses to Nutrients, Stresses, and Hormones in Arabidopsis      

Abstract

The Arabidopsis (Arabidopsis thaliana) gene BT2 encodes a 41-kD protein that possesses an amino-terminal BTB domain, a central TAZ domain, and a carboxyl-terminal calmodulin-binding domain. We previously demonstrated that BT2 could activate telomerase expression in mature Arabidopsis leaves. Here, we report its distinct role in mediating diverse hormone, stress, and metabolic responses. We serendipitously discovered that steady-state expression of BT2 mRNA was regulated diurnally and controlled by the circadian clock, with maximum expression in the dark. This pattern of expression suggested that BT2 mRNA could be linked to the availability of photosynthate in the plant. Exogenous sugars decreased BT2 expression, whereas exogenous nitrogen increased expression. bt2 loss-of-function mutants displayed a hypersensitive response to both sugar-mediated inhibition of germination and abscisic acid (ABA)-mediated inhibition of germination, thus supporting a role of ABA in sugar signaling in germination and development. Moreover, constitutive expression of BT2 imparted resistance to both sugars and ABA at germination, suggesting that BT2 suppresses sugar and ABA responses. In support of the previously described antagonistic relationship between ABA and auxin, we found that BT2 positively regulated certain auxin responses in plants, as revealed by knocking down BT2 expression in the high-auxin mutant yucca. Accumulation of BT2 mRNA was affected by a variety of hormones, nutrients, and stresses, and BT2 was required for responses to many of these same factors. Together, these results suggest that BT2 is a central component of an interconnected signaling network that detects and responds to multiple inputs.

Mutations in the Arabidopsis Homolog of LST8/GβL, a Partner of the Target of Rapamycin Kinase, Impair Plant Growth, Flowering, and Metabolic Adaptation to Long Days

“…and BTB-TAZ4 genes, which were previously shown to be induced by nitrate but repressed by sugars (Mandadi et al, 2009). The inhibition of the TOR kinase results in the induction of autophagy (Wullschleger et al, 2006).…”

Coping with Stresses: Roles of Calcium- and Calcium/Calmodulin-Regulated Gene Expression

“…At-BT1 and 2 localize to the nucleus and cytosol, whereas At-BT3, 4, and 5 are cytosolic (Robert et al, 2009). At-BT proteins participate in Arabidopsis development, metabolic processes, and hormone signaling (Ren et al, 2007;Mandadi et al, 2009;Robert et al, 2009), and a role in abiotic stress has been suggested as they exhibit differential expression upon exposure to salt (At-BT2, 3, and 4) and cold stress (At-BT2, 3, and 5) (Du and Poovaiah, 2004;Mandadi et al, 2009). Furthermore, At-BT1, 2, and 5 are induced in plants overexpressing the salt toleranceconferring TF At-bZIP60, suggesting involvement of these At-BT proteins in protecting plants from salt stress (Fujita et al, 2007).…”

Characterization of a Viral Synergism in the MonocotBrachypodium distachyonReveals Distinctly Altered Host Molecular Processes Associated with Disease

“…For all qRT-PCR analysis, three independent biological replicates consisting of three plant samples each were used for total RNA isolation using Trizol reagent (Ambion), following the manufacturer's instructions. Two micrograms of the total RNA was used to make cDNA using SuperScript III first-strand cDNA synthesis kit (Invitrogen), as described previously (Mandadi et al, 2009), with minor modifications. Gene amplification by PCR was performed using Power SYBR Green Master-mix and the ABI Prism 7500 sequence detection system (Applied Biosystems).…”