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Abstract

The synthesis and deactivation of bioactive
gibberellins (GA) are regulated by auxin and by GA signalling.
The effect of GA on its own pathway is mediated
by DELLA proteins. Like auxin, the DELLAs promote GA
synthesis and inhibit its deactivation. Here, we investigate
the relationships between auxin and DELLA regulation of
the GA pathway in stems, using a pea double mutant that is
deficient in DELLA proteins. In general terms our results
demonstrate that auxin and DELLAs independently
regulate the GA pathway, contrary to some previous suggestions.
The extent to which DELLA regulation was able
to counteract the effects of auxin regulation varied from
gene to gene. For Mendel’s LE gene (PsGA3ox1) no
counteraction was observed. However, for another synthesis
gene, a GA 20-oxidase, the effect of auxin was weak
and in WT plants appeared to be completely over-ridden by
DELLA regulation. For a key GA deactivation (2-oxidase)
gene, PsGA2ox1, the up-regulation induced by auxin deficiency
was reduced to some extent by DELLA regulation. A
second pea 2-oxidase gene, PsGA2ox2, was up-regulated by
auxin, in a DELLA-independent manner. In Arabidopsis
also, one 2-oxidase gene was down-regulated by auxin while
another was up-regulated. Monitoring the metabolism pattern
of GA20 showed that in Arabidopsis, as in pea, auxin
can promote the accumulation of bioactive GA.

Item Type:	Article
Authors/Creators:	O'Neill, DP and Davidson, SE and Clarke, VC and Yamauchi, Y and Yamaguchi, S and Kamiya, Y and Reid, JB and Ross, JJ
Journal or Publication Title:	Planta
ISSN:	0032-0935
DOI / ID Number:	10.1007/s00425-010-1248-0
Additional Information:	The final publication is available at http://www.springerlink.com
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