Plant Physiol, March 2001, Vol. 125, pp. 1363-1379
B-Bolivia, an Allele of the Maize b1 Gene
with Variable Expression, Contains a High Copy Retrotransposon-Related
Sequence Immediately Upstream1
David A.
Selinger and
Vicki L.
Chandler*
Department of Plant Sciences, University of Arizona, Tucson,
Arizona 85721
The maize (Zea mays) b1 gene encodes a
transcription factor that regulates the anthocyanin pigment pathway. Of
the b1 alleles with distinct tissue-specific expression,
B-Peru and B-Bolivia are the only alleles
that confer seed pigmentation. B-Bolivia produces
variable and weaker seed expression but darker, more regular plant
expression relative to B-Peru. Our experiments
demonstrated that B-Bolivia is not expressed in the seed
when transmitted through the male. When transmitted through the female
the proportion of kernels pigmented and the intensity of pigment
varied. Molecular characterization of B-Bolivia
demonstrated that it shares the first 530 bp of the upstream region
with B-Peru, a region sufficient for seed expression.
Immediately upstream of 530 bp, B-Bolivia is completely
divergent from B-Peru. These sequences share sequence similarity to retrotransposons. Transient expression assays of various
promoter constructs identified a 33-bp region in
B-Bolivia that can account for the reduced aleurone
pigment amounts (40%) observed with B-Bolivia relative
to B-Peru. Transgenic plants carrying the
B-Bolivia promoter proximal region produced pigmented seeds. Similar to native B-Bolivia, some transgene loci
are variably expressed in seeds. In contrast to native
B-Bolivia, the transgene loci are expressed in seeds
when transmitted through both the male and female. Some transgenic
lines produced pigment in vegetative tissues, but the
tissue-specificity was different from B-Bolivia, suggesting the introduced sequences do not contain the
B-Bolivia plant-specific regulatory sequences. We
hypothesize that the chromatin context of the B-Bolivia
allele controls its epigenetic seed expression properties, which could
be influenced by the adjacent highly repeated retrotransposon
sequence.
1
This work was supported by a postdoctoral
fellowship from the Jane Coffin-Childs Memorial Fund for Medical
Research (to D.A.S.), by a grant from the U.S. Department of
Agriculture National Research Initiative (grant no. 96-35301-3179 to
V.L.C.), and by the Department of Army Research for the purchase of the
Molecular Dynamics Storm 860 system used in this work (grant no. DAAG559710102).
*
Corresponding author; e-mail chandler{at}ag.arizona.edu; fax
520-621-7186.
© 2001 American Society of Plant Physiologists
