Transcriptional Regulation of ArabidopsisMIR168aandARGONAUTE1Homeostasis in Abscisic Acid and Abiotic Stress Responses  

Abstract

The accumulation of a number of small RNAs in plants is affected by abscisic acid (ABA) and abiotic stresses, but the underlying mechanisms are poorly understood. The miR168-mediated feedback regulatory loop regulates ARGONAUTE1 (AGO1) homeostasis, which is crucial for gene expression modulation and plant development. Here, we reveal a transcriptional regulatory mechanism by which MIR168 controls AGO1 homeostasis during ABA treatment and abiotic stress responses in Arabidopsis (Arabidopsis thaliana). Plants overexpressing MIR168a and the AGO1 loss-of-function mutant ago1-27 display ABA hypersensitivity and drought tolerance, while the mir168a-2 mutant shows ABA hyposensitivity and drought hypersensitivity. Both the precursor and mature miR168 were induced under ABA and several abiotic stress treatments, but no obvious decrease for the target of miR168, AGO1, was shown under the same conditions. However, promoter activity analysis indicated that AGO1 transcription activity was increased under ABA and drought treatments, suggesting that transcriptional elevation of MIR168a is required for maintaining a stable AGO1 transcript level during the stress response. Furthermore, we showed both in vitro and in vivo that the transcription of MIR168a is directly regulated by four abscisic acid-responsive element (ABRE) binding factors, which bind to the ABRE cis-element within the MIR168a promoter. This ABRE motif is also found in the promoter of MIR168a homologs in diverse plant species. Our findings suggest that transcriptional regulation of miR168 and posttranscriptional control of AGO1 homeostasis may play an important and conserved role in stress response and signal transduction in plants.

Salt Stress Reveals a New Role for ARGONAUTE1 in miRNA Biogenesis at the Transcriptional and Posttranscriptional Levels

“…These results support the idea of the involvement of AGO1 in the plant physiological response to salinity. A similar stress-related phenotype has already been described for another ago1 mutant, ago1-27 (Li et al, 2012b). However, no difference was observed between wild-type and ago1-11 plants when the expression of three salt-stress-related genes, ABF3, LEA4-5, and TSPO, was determined before and after NaCl treatment: in both wild-type and ago1-11 plants, overexpression of the stress marker genes was observed (Supplemental Fig.…”

“…Moreover, a more recent genome-wide analysis revealed that human AGO1 binds preferentially to active transcriptional enhancers and that this association is mediated by the RNAs that are transcribed from these enhancers, the eRNAs. Interestingly, the interaction of AGO1 with enhancers does not appear to regulate the transcription of neighboring genes but of alternative and constitutive splicing (Li et al, 2012b). Thus, in animal cells, the nuclear role of AGO1/2 proteins in the regulation of transcription and splicing has been well documented.…”

“…This interaction may also affect RNAPII processivity and abolish splicing of selected alternative exons (Ameyar-Zazoua et al, 2012;Li et al, 2012b;Alló et al, 2014). There have also been some suggestions that, in Arabidopsis, AGO1 localization is not limited to the cytoplasm (Ye et al, 2012;Duan et al, 2012).…”

“…It has been shown that AGO1 protein levels in plants increase during many different stresses, including salt stress (Vaucheret et al, 2006;Vaucheret 2009;Várallyay et al, 2010;Li et al, 2012b). To investigate whether a similar accumulation of AGO1 could also be observed under the experimental conditions used in our studies, we examined changes in AGO1 expression in Arabidopsis seedlings treated with NaCl at the transcript and protein levels.…”

Inference of Transcriptional Networks in Arabidopsis through Conserved Noncoding Sequence Analysis

“…Similarly, TFmiRNA regulation was studied by constructing a small subnetwork containing 24 TF-miRNA targets for 14 TFs and 10 target miRNAs (Supplemental Data Set 6). One of the retrieved interactions is the known binding of the ABRE BINDING FAC-TOR1 (ABF1) to the promoter of mir168a (Li et al, 2012). Another interesting, however unconfirmed, interaction is that between AP2 and mir167a, the latter which is known to play a role in flowering maturation (Rubio-Somoza and Weigel, 2013).…”