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Long-Day Up-Regulation of a GAMYB Gene during
Lolium temulentum Inflorescence Formation
Greg F.W. Gocal1,
Andrew T. Poole,
Frank Gubler,
Robyn
J. Watts,
Cheryl Blundell, and
Rod W. King*
Commonwealth Scientific and Industrial Research Organisation
(CSIRO) and Cooperative Research Centre for Plant Science, G.P.O. Box
4, Canberra, ACT 2601, Australia (G.F.W.G., A.T.P., F.G., R.J.W.); and CSIRO, Plant Industry, G.P.O. Box 1600, Canberra, ACT 2601, Australia
(C.B., R.W.K.)
Long-day exposure of the grass
Lolium temulentum may regulate flowering via changes in
gibberellin (GA) levels. Therefore, we have examined both GA levels and
expression of a MYB transcription factor that is
specific to the GA signal transduction pathway in monocots. This
MYB gene from L. temulentum shows over
90% nucleotide identity with the barley and rice GAMYB
genes, and, like them, gibberellic acid (GA3) up-regulates
its expression in the seed. Furthermore, cDNAs of both the barley and
L. temulentum GAMYB show the same simple patterns of
hybridization with digests of L. temulentum genomic
DNA. Compared with vegetative shoot apices of L. temulentum, the in situ mRNA expression of
LtGAMYB does not change during the earliest steps of
"floral" initiation at the apex. However, by 100 h (the
double-ridge stage of flowering) its expression increased substantially
and was highest in the terminal and lateral spikelet sites.
Thereafter, expression declined overall but then increased
within stamen primordia. Prior to increased LtGAMYB
expression, long-day exposure sufficient to induce flowering led to
increased (5- to 20-fold) levels of GA1 and GA4
in the leaf. Thus, increases first in GA level in the leaf followed by increased expression of LtGAMYB in the apex suggest
important signaling and/or response roles in flowering.
1
Present address: Plant Biology Laboratory, The
Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, San
Diego, CA 92037.
*
Corresponding author; e-mail r.king{at}pi.csiro.au; fax
61-26-246-5000.
Plant Physiol. (1999) 119: 1271-1278
Copyright Clearance Center: 0032-0889/99/119//08
© 1999 American Society of Plant Physiologists
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