Regulation of GA Biosynthesis Genes
during Germination and Young
Seedling Growth of Pea
(Pisum sativum L.)
Belay T. Ayele, Jocelyn A. Ozga,* and Dennis M. Reinecke
Plant Physiology and Molecular Biology Research Group, Department of Agricultural, Food and Nutritional Science, 4-10 Agriculture/
Forestry Centre, University of Alberta, Edmonton, Alberta T6G 2P5, Canada
A
BSTRACT
To explore the coordination and regulation of GA
biosynthesis during germination and early seedling
growth in pea, the developmental expression profile
of PsCPS1 [that codes for ent-copalyl diphosphate
synthase (CPS), which catalyses the first committed
step in gibberellin (GA) biosynthesis], and regulation
of expression of PsCPS1 and the late GA biosynthesis
genes were determined using real-time reverse
transcription polymerase chain reaction (RT-PCR).
Mature embryos contained PsCPS1 transcripts prior
to germination, suggesting that PsCPS1 mRNAs syn-
thesized during seed development were sequestered
in the mature embryo. PsCPS1 transcripts were de-
tected in all tissues examined during germination
and young seedling growth (cotyledons, embryo
axis, shoots, and roots from 0.5 to 6 days after imbi-
bition [DAI]) and were under tight developmental
regulation. PsCPS1 transcript abundance decreased
upon imbibition in the post-mitotic cotyledons and
remained low to 6 DAI. In contrast, PsCPS1 transcript
abundance increased in the actively growing embryo
axes, and the shoots and roots of the young seedlings.
PsCPS1 did not exhibit feed-back regulation at the
mRNA level in the roots or shoots of seedlings fol-
lowing modulation of bioactive GA levels (using GA
3
or prohexadione), whereas the late GA biosynthesis
genes showed either feed-back (PsGA20ox1 and
PsGA3ox1) or feed-forward (PsGA2ox1 and PsGA2ox2)
regulation, with one exception, PsGA20ox2, which
was not regulated in this manner. Our data also
suggest that at least part of the homeostatic mecha-
nism of the root to maintain lower levels of bioactive
GAs than in the shoot is through regulation of the
mRNA levels of the genes in the latter part of the GA
biosynthesis pathway.
Key words: Gene expression; Gibberellin
biosynthesis; Pisum sativum L.; Seed germination;
Seedling growth; Feed-back regulation; Feed-for-
ward regulation.
I
NTRODUCTION
Seed germination incorporates those events that
commence with the uptake of water by the quies-
cent dry seed (imbibition) and that terminate with
Received: 25 January 2006; accepted: 12 May 2006; Online publication:
26 September 2006
*Corresponding author; e-mail: jocelyn.ozga@ualberta.ca
J Plant Growth Regul (2006) 25:219–232
DOI: 10.1007/s00344-006-0007-8
219