Characterization of StABF1, a stress-responsive bZIP transcription factor from Solanum tuberosum L. that is phosphorylated by StCDPK2 in vitro

Abstract

ABF/AREB bZIP transcription factors mediate plant abiotic stress responses by regulating the expression of stress-related genes. These proteins bind to the abscisic acid (ABA)-responsive element (ABRE), which is the major cis-acting regulatory sequence in ABA-dependent gene expression. In an effort to understand the molecular mechanisms of abiotic stress resistance in cultivated potato (Solanum tuberosum L.), we have cloned and characterized an ABF/AREB-like transcription factor from potato, named StABF1. The predicted protein shares 45-57% identity with A. thaliana ABFs proteins and 96% identity with the S. lycopersicum SlAREB1 and presents all of the distinctive features of ABF/AREB transcription factors. Furthermore, StABF1 is able to bind to the ABRE in vitro. StABF1 gene is induced in response to ABA, drought, salt stress and cold, suggesting that it might be a key regulator of ABA-dependent stress signaling pathways in cultivated potato. StABF1 is phosphorylated in response to ABA and salt stress in a calcium-dependent manner, and we have identified a potato CDPK isoform (StCDPK2) that phosphorylates StABF1 in vitro. Interestingly, StABF1 expression is increased during tuber development and by tuber-inducing conditions (high sucrose/nitrogen ratio) in leaves. We also found that StABF1 calcium-dependent phosphorylation is stimulated by tuber-inducing conditions and inhibited by gibberellic acid, which inhibits tuberization.

CDPK1 from Ginger Promotes Salinity and Drought Stress Tolerance without Yield Penalty by Improving Growth and Photosynthesis in Nicotiana tabacum

“…StCDPK1 expression was shown to be specifically up-regulated by sucrose and sorbitol; hence osmotic stress activation of sucrose-phosphate synthase leading to in vitro tuber induction was discussed. In continuum StCDPK2, a potato CDPK isoform, phosphorylates StABF1, a tuber development responsive bZIP transcription factor in vitro [60]. …”

StCDPK3 Phosphorylates In Vitro Two Transcription Factors Involved in GA and ABA Signaling in Potato: StRSG1 and StABF1

“…Its expression is induced in response to ABA, drought, salt stress, and cold, and increased during tuber development [54]. StABF1 presents five serine and two threonine residues in an RXXS/T context that could be targeted by kinases and is phosphorylated in response to ABA and salt stress in a calcium-dependent manner.…”

“…Moreover, StABF1 calcium-dependent phosphorylation is stimulated by tuber-inducing conditions and is inhibited by GA. The potato StCDPK2 isoform phosphorylates StABF1 in vitro [54]. Since St CDPK 3 expression was enhanced by ABA [43], it was worth testing the ability of 6xHisStCDPK3 to phosphorylate StABF1, as an alternative substrate to StRSG1.…”

“…On the other hand, Arabidopsis CPK12 is a negative regulator of ABA signaling in seed germination and post-germination growth; CPK12 -RNAi lines resulted in ABA-hypersensitivity [60]. According to previous results, StABF1 TF mediates the function of ABA during tuberization [54]. Transgenic potato plants that overexpress ABF4 or ABF2 from Arabidopsis show increased tuber induction.…”

“…Thus, it could be suggested that ABF TFs function in potato ABA-GA signaling crosstalk during tuberization. In vitro , StABF1 is phosphorylated by StCDPK2 [54] and by StCDPK3 (Fig 4). StCDPK2 and 3 differ in their expression pattern, in their kinetic parameters, and in the Ca 2+ concentration required for full activation [42,43].…”