National Institute for Basic Biology

Division of Gene Expression and Regulation I

Shigeru Iida
Research Associates:
Rie Terada
Yoshiki Habu
Graduate Students:
Yasuyo Hisatomi
Atsushi Hoshino
Technical Staff:
Sachiko Tanaka-Fukada

This group's move along the Tokaido line from Department of Biological Science and Technology, Science University of Tokyo, begun in April and its formation continued throughout the year. The main interest of the group is in understanding the biology of dynamic genome, namely, genome organization and reorganization and their impact on gene expression and regulation.

Although there are many elements affecting organization and reorganization of the genomes, we have currently focused on mobile genetic elements in general and plant transposable controlling elements in particular.

I. Identification and characterization of mutable alleles in the Japanese morning glory

The Japanese morning glory (Pharbitis nil or Ipomoea nil) is a traditional horticultural plant in Japan, and extensive physiological and genetical studies on the plant have been conducted. Among several mutable loci that condition variegated flower phenotypes, two mutable alleles, flecked and speckled have been chosen for molecular elucidation of the variegated phenotypes.

The flecked mutant bearing white flowers with colored flecks and sectors (Fig. 1A). The flecking was regarded as recurrent somatic mutation from the recessive white to the dominant pigmented allele, accompanied by changes in genotypes from the homozygous recessive to the heterozygous condition. We have molecularly characterized the flecked mutation in one of the anthocyanin genes, A-3, and found that the mutable a-3flecked (flecked) allele carries a transposable element of 6412 bp, termed Tpn1, in the anthocyanin biosynthesis gene for dihydroflavonol 4-reductase (DFR). Among the three copies of the DFR gene in the genome of the Japanese morning glory, Tpn1 resides within the second intron 9 bp upstream of the third exon of the DFR-B gene. The flower variegation is shown to be due to somatic reversion of the DFR-B gene by Tpn1 excision (see Inagaki et al. (1996) Theor. Appl. Genet. 92, 499-504). Structural characteristics revealed that Tpn1 belongs to En/Spm family of elements and that it is likely to be a non-autonomous element deficient to produce active transposases.

It is known that the frequency and the timing of the flecking phenotypes in the mutable a-3flecked line are generally heritable by their progeny but sometimes conversion of these phenotypes is also observed. Thus the flecking phenotypes caused by the excision of Tpn1 from the DFR-B gene may be determined either by trans-acting activities of its related autonomous element or by heritable modifications of Tpn1 itself. We are currently focusing on these lines of investigations.

Fig. 1B shows another flower variegation caused by the mutable speckled allele. Our genetic studies indicate that another element termed speckled-activator acting in trans on the speckled allele is necessary to confer the speckled variegation phenotype. Our current hypothesis is that the mutable speckled allele carries a non-autonomous transposable element and speckled-activator must be a related autonomous element. To test this hypothesis, we are trying to identify the mutable speckled allele.

II. Identification of the mutable alleles in the common morning glory

The mutable aflaked line of the common morning glory (Pharbitis purpurea or Ipomoea purpurea) also bears white flowers with colored flakes and sectors (Fig. 1C). The mutable aflaked allele is known to exhibit incomplete dominance. Interestingly, not only intensely colored flakes but also white spots and sectors were often observed in lightly colored flowers of morning glory with the heterozygous state A/aflaked. To understand these allelic interactions in molecular terms, we are trying to identify the mutable aflaked allele. Although several new mobile genetic elements have been found in the mutable line, we are still in process of identifying the mutable aflaked allele.

Fig. 1.
Flower variegation. (A) a-3flecked; (B) speckled; (C) aflaked.
Last Modified: 12:00, June 27, 1997