Insights into the molecular mechanism of RGL2-mediated inhibition of seed germination in Arabidopsis thaliana

Abstract

BackgroundSeed germination is of immense significance for agriculture and has been studied for centuries. Yet, our understanding of the molecular mechanisms underlying regulation of dormancy and germination is still in its infancy. Gibberellins are the key phytohormones that promote germination, and the DELLA protein RGL2 is the main signalling intermediate involved in this response. Germination is completely inhibited if functional RGL2 is overexpressed and/or stabilized; however, the molecular mechanisms of RGL2 function are still largely unknown. We therefore attempted to shed light onto some of the genetic events downstream of RGL2.ResultsGene ontology of the transcriptome differentially regulated by RGL2, as well as extensive cross-comparison with other available microarray data indicates that RGL2-mediated inhibition of germination causes seeds to enter a state of dormancy. RGL2 also appears to differentially regulate a number of transcription factors, many of which are known to be involved in light- or phytohormone-mediated aspects of germination. A promoter analysis of differentially expressed genes identified an enrichment of several motifs that can be bound by specific transcription factors, for example GAMYB, ARF1, or Dof-type zinc fingers. We show that Dof-binding motifs indeed play a role in RGL2-mediated transcription. Using Chromatin Immunoprecipitation (ChIP), we show that RGL2 directly downregulates at least one cell wall modifying enzyme, which is predicted to constrain cell growth thereby leading to inhibition of seed germination.ConclusionsOur results reveal that RGL2 controls various aspects of germination. Through the repression of cell wall modifying enzymes, cell growth is directly constrained to inhibit germination. Furthermore, RGL2 likely interacts with various types of proteins to regulate transcription, and differentially regulates several transcription factors. Collectively, our data indicate that gibberellins, acting via RGL2, control several aspects of seed germination.

AtGASA6 Serves as an Integrator of Gibberellin-, Abscisic Acid- and Glucose-Signaling during Seed Germination in Arabidopsis

“…1). This expression pattern is consistent with the finding that AtGASA6 expression is repressed in the RGL2-mediated seed germination transcriptome (Stamm et al, 2012). Our results show that, under condition, with added PAC, the highest seed germination rates of rgl2-13 were reduced by the loss of AtGASA6 function (Fig.…”

“…Therefore, we hypothesized the existence of a direct physical interaction between AtGASA6 and AtEXPA1, but this was not supported by bimolecular fluorescence complementation and yeast (Saccharomyces cerevisiae) two-hybrid analyses (data not shown). In the RGL2-regulated seed germination transcriptome, several EXPA genes, including AtEXPA1, AtEXPA3, AtEXPA8, and AtEXPA9, are repressed by RGL2 (Stamm et al, 2012). AtEXPA2 is also involved in seed germination and abiotic stress responses, and its expression levels in germinating seeds are repressed by expression of DELLA genes, including RGL1, RGL2, RGA, and GAI (Yan et al, 2014).…”

“…Previous transcriptome data suggest that several GASA and EXPANSIN family genes, which encode putative cell wall localized proteins, likely function in GA-mediated seed germination (Gonzali et al, 2006;Stamm et al, 2012). To verify this, we evaluated their expressions in imbibed della mutant seeds and found that only AtGASA6 (At1g74670) and Arabidopsis expansin A1 (AtEXPA1; At1g69530) are up-regulated in rga24-, gai-t6-, rgl2-1-, and gai-t6/rga-24-imbibed seeds (Fig.…”

DELLA Proteins and Their Interacting RING Finger Proteins Repress Gibberellin Responses by Binding to the Promoters of a Subset of Gibberellin-Responsive Genes inArabidopsis

“…Flowering time was determined by counting rosette leaves at bolting (SD, n = 10; *significant difference from the wild type; **significant difference from the gai-1 mutant; P < 0.05, Student's t test). DELLAs are also known to target and regulate various gene promoters (Zentella et al, 2007;Gallego-Bartolomé et al, 2011;Stamm et al, 2012). Since BOIs and DELLAs interact, we hypothesized that the two protein families could target and regulate the same regulatory regions of genes.…”

The Arabidopsis MYB96 Transcription Factor Is a Positive Regulator of ABSCISIC ACID-INSENSITIVE4 in the Control of Seed Germination

“…They interact with transcription factors to allow DELLAs to regulate gene expression by targeting specific gene promoters (de Lucas et al, 2008;Feng et al, 2008;Arnaud et al, 2010;GallegoBartolomé et al, 2010;Hong et al, 2012). Indeed, DELLAs bind to promoters of GIBBERELLIN INSENSITIVE DWARF1, WRKY27, and SCARECROW-LIKE3 to control seed germination (Zentella et al, 2007;Gallego-Bartolomé et al, 2011;Zhang et al, 2011;Stamm et al, 2012). The DELLA proteins are rapidly degraded in response to GA and are thus considered as repressors of seed germination in the absence of GA (Dill et al, 2001;Tyler et al, 2004).…”