Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: KARYOTYPING AND CHROMOSOMAL GENE AND PHYSICAL MAPPING OF
CHLORELLA: THE SMALLEST PLANT CHROMOSOME
KARYOTYPING AND CHROMOSOMAL GENE AND PHYSICAL MAPPING OF
CHLORELLA: THE SMALLEST PLANT CHROMOSOME.
Takashi Yamada, Takanobu Higashiyama, and Jun Takehara,
Department of Fermentation Technology, Faculty of Engineering,
Hiroshima University, Higashi-Hiroshima 724, Japan and Technical
Research Center, Chugoku Electric Power Co. Inc.,Hiroshima 732,
Japan.
Molecular karyotypes for eight strains of four Chlorella
species were obtained by using an alternating-field gel
electrophoresis system which employs contour-clamped homogeneous
electric field (CHEF). The number and migration pattern of the
chromosomal DNA molecules varied greatly from strain to strain:
for example, 9 separated chromosomes of C. ellipsoidea C87 (C.
saccharophila 211-1a) ranged from 2.5 to 6.5 megabase pairs (mbp)
in size, whereas 16 chromosomes of C. vulgaris C169 were from 980
kilobase pairs (kbp) to 4.0 mbp [T. Higashiyama and T. Yamada,
Nucleic Acids Res, 19, 6191-6195 (1991)]. In spite of the
different chromosome separation patterns, the sum of the
chromosome sizes was almost the same, 38-39 mbp for all Chlorella
strains tested. This genome size is approximately twice that of
Saccharomyces cerevisiae and half the size of Arabidopsis
thaliana. Since the, smallest chromosome (I) of C169 strain (980
kbp) can be easily separated by CHEF gel electrophoresis, it
would serve as an excellent material to study the fundamental
molecular structure of plant-type chromosomes. So far, a NotI
physical map has been constructed for C169-I chromosome. Using
hybridization techniques, several specific genes as well as
clones of a C169-I library were localized on this map.
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