PLANT PHYSIOLOGY , Vol 103, Issue 3 703-711, Copyright © 1993 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Differential Expression of Myrosinase Gene Families
M. Lenman, A. Falk, J. Rodin, A. S. Hoglund, B. Ek and L. Rask
Uppsala Genetic Center, Department of Cell Research, Swedish University of Agricultural Sciences, Box 7055, S-750 07 Uppsala, Sweden
In mature seeds of Brassica napus three major and three minor myrosinase
isoenzymes were identified earlier. These myrosinases are known to be
encoded by at least two different families of myrosinase genes, denoted MA
and MB. In the work described in this paper the presence of different
myrosinase isoenzymes in embryos, seedlings, and vegetative mature tissues
of B. napus was studied and related to the expression of myrosinase MA and
MB genes in the same tissues to facilitate future functional studies of
these enzymes. In developing seeds, myrosinases of 75, 73, 70, 68, 66, and
65 kD were present. During seedling development there was a turnover of the
myrosinase pool such that in 5-d-old seedlings the 75-, 70-, 66-, and 65-kD
myrosinases were present, with the 70- and 75-kD myrosinases predominating.
In 21-d-old seedlings the same myrosinases were present, but the 66- and
65-kD myrosinase species were most abundant. At flowering the mature organs
of the plant contained only a 72-kD myrosinase. MA genes were expressed
only in developing seeds, whereas MB genes were most highly expressed in
seeds, seedling cotyledons, young leaves, and to a lesser extent other
organs of the mature plant. During embryogenesis of B. napus, myrosinase MA
and MB gene transcripts started to accumulate approximately 20 d after
pollination and reached their highest level approximately 15 d later. MB
transcripts accumulated to about 3 times the amount of MA transcripts. In
situ hybridization analysis of B. napus embryos showed that MA transcripts
were present predominantly in myrosin cells in the axis, whereas MB genes
were expressed in myrosin cells of the entire embryo. The embryo axis
contained 75-, 70-, and 65-kD myrosinases, whereas the cotyledons contained
mainly 70- and 65-kD myrosinases. Amino acid sequencing revealed the 75-kD
myrosinase to be encoded by the MA gene family. The high degree of cell and
tissue specificity of the expression of myrosinase genes suggests that
studies of their transcription should provide interesting information
concerning a complex type of gene regulation.
