Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 69pg1
COMPLEX GENE FAMILIES OF LOBLOLLY PINE.
Claire S. Kinlaw and Suzanne Gerttula. Institute of Forest
Genetics, Pacific Southwest Research Station, USDA Forest
Service, PO Box 245, Berkeley, California, 94701.
Conifer genomes in general, and pine genomes in particular,
are among the largest in the plant kingdom. For example,
loblolly pine (Pinus taeda) contains 10pg DNA per haploid genome
as compared to 0.1 pg per Arabidopsis haploid genome. Conifer
genomes, like angiosperm genomes, contain much repeated sequence
DNA. Unlike angiosperms, a significant part of the repeated pine
DNA may fall into complex gene families. As a result of the pine
genome mapping project (David Neale and co-workers), it has been
observed that many random cDNAs hybridize to multiple bands on
Southern blots. "Single copy" banding patterns are only rarely
observed for loblolly pine cDNAs, and approximately 25% of all
random cDNAs from loblolly pine seedling mRNA hybridize to more
bands than can be easily counted (>l0). We have begun an
investigation into the primary structure, function, genome
organization, and evolution of a number of these complex pine
gene families. We have performed Southern blots with copy number
reconstructions to estimate a minimum gene family sizes, and we
have compared Southern banding patterns between loblolly pine a
hard pine (Pinus subgenus of the genus Pinus) and western white
pine (Pinus monticola) a soft pine (Stobus subgenus of the genus
Pinus). Gene families sizes for the clones chosen, range from 4
to approximately 20. Hybridization intensities vary among
Southern bands for each particular cDNA, suggesting considerable
sequence heterogeneity among gene family members. Hybridization
of loblolly pine cDNAs to western white pine genomic DNA vs.
loblolly pine genomic DNA results in fewer bands of lower
intensity, suggesting that some members of pine complex gene
families have diverged beyond detectable limits between the two
halves of the pine genus. We have determined the mRNA sizes from
northern blots and DNA sequence for each cDNA, and used the DNA
sequence to compare to DNA sequences from GenBank. Approximately
10% of the cDNAs analyzed show clear sequence similarity to plant
sequences in GenBank. One particular clone, IFGp2027, appears to
be a non-specific pine lipid transfer protein, based upon
nucleotide sequence similarity, conservation of key amino acids,
small size, basic pi, and similarity of hydropathy plots. This
protein has been shown to be under developmental, cell specific,
and environmental control in angiosperms (S.Torres-Schumann,
Plant Mol. Biol. 18: 749-757). In loblolly pine, this lipid
transfer protein is a highly abundant message in seedlings,
perhaps as high as 10% of the poly A+ RNA.
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