Regulation of Gibberellin 20-Oxidase and Gibberellin 3β-Hydroxylase Transcript Accumulation during De-Etiolation of Pea Seedlings

Abstract

Gibberellin (GA) 20-oxidase (GA 20-ox) and GA 3β-hydroxylase (GA 3β-hy) are enzymes that catalyze the late steps in the formation of active GAs, and are potential control points in the regulation of GA biosynthesis by light. We have investigated the photoregulation of the GA 20-ox and GA 3β-hy transcript levels in pea (Pisum sativum L.). The GA 20-oxtranscript level was higher in light-grown seedlings than in etiolated seedlings, whereas GA 3β-hy mRNA accumulation was higher in etiolated seedlings. However, transfer of etiolated seedlings to light led to a 5-fold increase in the expression of both transcripts 4 h after transfer. GA 20-ox mRNA accumulation is regulated by both phytochromes A and B. Transfer to light also resulted in a 6-fold decrease in GA1 levels within 2 h. These results suggest that the light-induced drop in GA1 level is not achieved through regulation of GA 20-ox andGA 3β-hy mRNA accumulation. The application of exogenous GA1 to apical buds of etiolated seedlings prior to light treatments inhibited the light-induced accumulation of bothGA 20-ox and GA 3β-hy mRNA, suggesting that negative feedback regulation is an important mechanism in the regulation of GA 20-ox and GA 3β-hymRNA accumulation during de-etiolation of pea seedlings.

DELLAs Contribute to Plant Photomorphogenesis

“…Previous studies have shown GAs promote skotomorphogenetic growth of Arabidopsis and pea (Pisum sativum) seedlings grown in darkness (Cowling and Harberd, 1999;Alabadí et al, 2004). Furthermore, a rapid decrease in the levels of bioactive GA 1 has been observed upon transfer of etiolated pea seedlings into light (Ait-ali et al, 1999;Gil and García-Martinez, 2000;O'Neill et al, 2000). Here we have shown that Arabidopsis GA metabolism gene transcript levels change rapidly in response to changes in the light environment.…”

“…Reed et al, 1996;Ait-ali et al, 1999;Alabadí et al, 2004), none have systematically investigated the role of DELLAs in light-mediated growth regulation. Recent advances have led to the development of Arabidopsis mutant lines that are multiply DELLA deficient and to the use of these lines in experiments that reveal the role of DELLAs in many aspects of plant growth and development, including those that are influenced by environmental conditions (Lee et al, 2002;Cheng et al, 2004;Yu et al, 2004;Cao et al, 2005;Achard et al, 2006).…”

Diurnal Regulation of the Brassinosteroid-Biosynthetic CPD Gene in Arabidopsis

“…Remarkably, most lightresponsive genes of GA synthesis were also found to be under wavelength-or photoreceptor-specific control. In Arabidopsis, lettuce (Lactuca sativa), and pea (Pisum sativum), light was shown to regulate the expression of GA 3b-hydroxylase and GA 20-oxidase isoforms via either phytochrome-dependent or -independent mechanisms (Toyomasu et al, 1998;Yamaguchi et al, 1998;Ait-Ali et al, 1999;Jackson et al, 2000).…”

Light Regulation of Gibberellin Biosynthesis in Pea Is Mediated through the COP1/HY5 Pathway

“…However, the clearest example of light-regulated hormone biosynthesis during deetiolation comes from pea (Pisum sativum), where transfer of etiolated pea seedlings to light induces a rapid drop in levels of the active GA (GA 1 ), to <10% of dark levels within 4 h (Ait-Ali et al, 1999;Gil and García-Martinez, 2000;O'Neill et al, 2000;Symons and Reid, 2003). This drop is associated with changes in transcript levels of GA biosynthesis genes and depends on the activity of the phyA and cry1 photoreceptors (Reid et al, 2002;Foo et al, 2006).…”