Ectopic Expression of EFFECTOR OF TRANSCRIPTION Perturbs Gibberellin-Mediated Plant Developmental Processes

Abstract

The plant hormone gibberellin (GA) is known to modulate various aspects of plant cell differentiation and development. The current model of GA-mediated regulation is based on a de-repressible system and includes specific protein modification and degradation. HRT, a zinc finger protein from barley has been shown to have GA-dependent transcriptional repressing activity on the seed-specific alpha-amylase promoter [Raventos, D., Skriver, K., Schlein, M., Karnahl, K., Rogers, S.W., Rogers, J.C. and Mundy, J. 1998. J. Biol. Chem. 273: 23313-23320]. Here we report the characterization of a dicot homologue from Brassica napus (BnET) and provide evidence for its role in GA response modulation suggesting that this could be a conserved feature of this gene family. When BnET is ectopically expressed in either Arabidopsis or tobacco the phenotypes include dwarfism due to shorter internodes and late flowering, reduced germination rate, increased anthocyanin content and reduced xylem lignification as a marker for terminal cell differentiation. Transient expression in protoplasts supports the notion that this most likely is due to a transcriptional repression of GA controlled genes. Finally, histological analysis showed that in contrast to other GA deficient mutants the shorter internodes were due to fewer but not smaller cells, suggesting a function of BnET in GA-mediated cell division control.

Transcriptional regulator AtET2 is required for the induction of dormancy during late seed development

“…A search for novel regulators of seed maturation led to the isolation of the ET genes (Raventos et al, 1998;Ellerstrom et al, 2005). They encode proteins implicated in control of GA responses and cell differentiation as transcriptional regulators.…”

“…Overexpression of the Brassica napus homolog, BnET, in tobacco (Nicotiana tabacum) and Arabidopsis leads to dwarfism and differentiation defects, fully supporting the observations in the et2-1 Arabidopsis mutant. Furthermore, leaf cells overexpressing BnET fail to de-differentiate and produce callus under favorable in vitro conditions, indicating that constant presence of ET in the cell drives irreversibly the differentiation program (Ellerstrom et al, 2005).…”

“…Additionally, all known ET proteins seem to be involved in regulating either GA-inducible promoters in vitro (Raventos et al, 1998;Ellerstrom et al, 2005;Ivanov et al, 2008), or GA biosynthesis and response genes in plants (Ellerstrom et al, 2005;Ivanov et al, 2008). ET proteins localize to the nucleus in differentiating cells (Raventos et al, 1998;Ellerstrom et al, 2005;Ivanov et al, 2008), but are rather unexpectedly also present in cytoplasmic compartments in undifferentiated cells (Ivanov et al, 2008). This probably represents a general mechanism for storage of inactive protein as suggested also for other transcription factors (Ryu et al, 2007;Lindermayr et al, 2010), transmembrane proteins (Ivanov and Gaude, 2009a,b;Barberon et al, 2011), etc.…”

“…However, the factors from monocot and dicot species seem to differ in their binding specificity. The barley HRT binds GA-response elements (GAREs) (Raventos et al, 1998), while BnET shows no sequence preference when binding (Ellerstrom et al, 2005). For its activity as a transcriptional regulator, the Arabidopsis AtET2 was demonstrated to require a functional nuclease domain.…”

Characterization of the gibberellic acid response of the Brassica napus L. em. Metzg. dwarf mutant NDF-1

“…In B. napus, the very important oil crop with large potential in food and biofuel, although some dwarf mutants have been described (Zanewich et al 1991;Muangprom and Osborn 2004;Ellerström et al 2005;Muangprom et al 2006), our understanding of the reason of dwarfism is still very limited. A novel dwarf mutant of B. napus, NDF-1, obtained from a high stemmed line '3529', has been described as a useful germplasm for oilseed rape breeding program (Wang et al 2004).…”