Abstract
Serine/arginine-rich (SR) proteins are major modulators of alternative splicing, a key generator of proteomic diversity and flexible means of regulating gene expression likely to be crucial in plant environmental responses. Indeed, mounting evidence implicates splicing factors in signal transduction of the abscisic acid (ABA) phytohormone, which plays pivotal roles in the response to various abiotic stresses. Using real-time RT-qPCR, we analyzed total steady-state transcript levels of the 18 SR and two SR-like genes from Arabidopsis thaliana in seedlings treated with ABA and in genetic backgrounds with altered expression of the ABA-biosynthesis ABA2 and the ABA-signaling ABI1 and ABI4 genes. We also searched for ABA-responsive cis elements in the upstream regions of the 20 genes. We found that members of the plant-specific SC35-Like (SCL) Arabidopsis SR protein subfamily are distinctively responsive to exogenous ABA, while the expression of seven SR and SR-related genes is affected by alterations in key components of the ABA pathway. Finally, despite pervasiveness of established ABA-responsive promoter elements in Arabidopsis SR and SR-like genes, their expression is likely governed by additional, yet unidentified cis-acting elements. Overall, this study pinpoints SR34, SR34b, SCL30a, SCL28, SCL33, RS40, SR45 and SR45a as promising candidates for involvement in ABA-mediated stress responses.
Highlights
In agreement with our results, the SCL33 gene has been previously described as being downregulated by abscisic acid (ABA) but, contrary to what we report, SCL28 and SCL30a were found to be unaffected by ABA treatment [40]
We focused our attention on two well-characterized elements shown to confer responsiveness to ABA: the ACGT-containing ABA-responsive element (ABRE) and the functionally equivalent non-ACGT containing element known as Coupling Element 3 (CE3) [81,82,83,84,85] (Figure 6A)
Given that many pre-mRNA splicing factors are beginning to be implicated in ABA-mediated stress responses, we screened the 20 Arabidopsis thaliana genes encoding SR or SR-related proteins for total expression changes induced by exogenous ABA treatment or in different genetic backgrounds with alterations in key ABA pathway components
Summary
Precursor messenger RNA (pre-mRNA) splicing is an essential step in gene expression mediated by the spliceosome, a large protein complex in the cell nucleus that interacts with specific intronic sequences in the pre-mRNA called splice sites for the proper removal of introns and correct joining of exons. Stress-associated genes are prone to AS [32,33,34], which is markedly affected by abiotic stresses [32,35,36,37,38,39], and the expression/splicing pattern of several SR or SR-like proteins is stress-regulated [38,40,41,42], pointing to a crucial role for AS in plant responses to environmental stress. The SR-like SR45 protein negatively regulates glucose signaling during early seedling development in Arabidopsis by downregulating the ABA pathway [16] These findings suggest that posttranscriptional networks may act as central coordinators of plant abiotic stress responses by targeting key components of the ABA signal transduction machinery. ABFs, we examined upstream sequences for each of the SR and SR-like genes for occurrences of putative ABRE cis elements
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