Characterization of Evolutionarily Conserved Motifs Involved in Activity and Regulation of the ABA-INSENSITIVE (ABI) 4 Transcription Factor

Abstract

In recent years, the transcription factor ABI4 has emerged as an important node of integration for external and internal signals such as nutrient status and hormone signaling that modulates critical transitions during the growth and development of plants. For this reason, understanding the mechanism of action and regulation of this protein represents an important step towards the elucidation of crosstalk mechanisms in plants. However, this understanding has been hindered due to the negligible levels of this protein as a result of multiple posttranscriptional regulations. To better understand the function and regulation of the ABI4 protein in this work, we performed a functional analysis of several evolutionarily conserved motifs. Based on these conserved motifs, we identified ortholog genes of ABI4 in different plant species. The functionality of the putative ortholog from Theobroma cacao was demonstrated in transient expression assays and in complementation studies in plants. The function of the highly conserved motifs was analyzed after their deletion or mutagenesis in the Arabidopsis ABI4 sequence using mesophyll protoplasts. This approach permitted us to immunologically detect the ABI4 protein and identify some of the mechanisms involved in its regulation. We identified sequences required for the nuclear localization (AP2-associated motif) as well as those for transcriptional activation function (LRP motif). Moreover, this approach showed that the protein stability of this transcription factor is controlled through protein degradation and subcellular localization and involves the AP2-associated and the PEST motifs. We demonstrated that the degradation of ABI4 protein through the PEST motif is mediated by the 26S proteasome in response to changes in the sugar levels.

TOR-inhibitor insensitive-1 (TRIN1) regulates cotyledons greening in Arabidopsis

“…Early studies have shown that the degradation of ABI4 is crucial for its functions in plant growth and development (Gregorio et al, 2014 ). To determine whether TOR regulates the stability of TRIN1 protein in Arabidopsis , we fused TRIN1 with GUS and generated P35S::TRIN1-GUS transgenic plants.…”

Emerging roles of protein kinase CK2 in abscisic acid signaling

“…The stabilization of ABF1 and ABF3 by ABA is thought to be achieved by phosphorylation by SnRK2 kinases, which in turn promotes the binding of 14–3–3 proteins ( Sirichandra et al, 2010 ). ABSCISIC ACID INSENSITIVE 4 (ABI4), a member of the DREB subfamily A-3 of ERF/AP2 transcription factors, is required for proper ABA signaling during seed development and germination ( Gregorio et al, 2014 ). Like ABI3 and ABI5, ABI4 is subject to a stringent post-transcriptional regulation that targets the protein to degradation and prevents it from accumulating to high levels.…”

Isolation of New Gravitropic Mutants under Hypergravity Conditions

“…Among the genes found in the region, ABI4 is known to play a role in sensitivity to abscisic acid during seed germination ( Finkelstein, 1994 ) and is highly expressed in seeds and weakly expressed in hypocotyls and shoots ( Finkelstein et al, 1998 ; Söderman et al, 2000 ). Previous studies have also suggested that ABI4 functions as a transcription factor ( Finkelstein et al, 1998 ; Gregorio et al, 2014 ). The eal1 ene1 mutant has a mutation in ABI4 that generates a stop codon (Gln205X) in a transcriptional activation region.…”