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Cucumber: A model angiosperm for mitochondrial transformation?

100%

Havey M. J., Lilly J. W., Bohanec B., Bartoszewski G., Malepszy S.

Journal of Applied Genetics

2002

vol. 43

issue 1

1-17

Plants possess three major genomes, carried in the chloroplast, mitochondrion, and nucleus. The chloroplast genomes of higher plants tend to be of similar sizes and structure. In contrast both the nuclear and mitochondrial genomes show great size differences, even among closely related species. The largest plant mitochondrial genomes exist in the genus Cucumis at 1500 to 2300 kilobases, over 100 times the sizes of the yeast or human mitochondrial genomes. Biochemical and molecular analyses have established that the huge Cucumis mitochondrial genomes are due to extensive duplication of short repetitive DNA motifs. The organellar genomes of almost all organisms are maternally transmitted and few methods exist to manipulate these important genomes. Although chloroplast transformation has been achieved, no routine method exists to transform the mitochondrial genome of higher plants. A mitochondrial-transformation system for a higher plant would allow geneticists to use reverse genetics to study mitochondrial gene expression and to establish the efficacy of engineered mitochondrial genes for the genetic improvement of the mitochondrial genome. Cucumber possesses three unique attributes that make it a potential model system for mitochondrial transformation of a higher plant. Firstly, its mitochondria show paternal transmission. Secondly, microspores possess relatively few, huge mitochondria. Finally, there exists in cucumber unique mitochondrial mutations conditioning strongly mosaic (msc) phenotypes. The msc phenotypes appear after regeneration of plants from cell culture and sort with specific rearranged and deleted regions in the mitochondrial genome. These mitochondrial deletions may be a useful genetic tool to develop selectable markers for mitochondrial transformation of higher plants.

Sequence characteristics and divergent evolution of the chloroplast psbA-trnH noncoding region in gymnosperms

100%

Hao D. C., Chen S. L., Xiao P. G.

vol. 51

issue 3

259-273

The psbA-trnH intergenic region is among the most variable regions in the gymnosperm chloroplast genome. It is proposed as suitable for DNA barcoding studies and is useful in phylogenetics at the species level. This region consists of two parts differing in their evolutionary characteristics: 1) the psbA 3'UTR (untranslated region) and 2) the psbA-trnH intergenic spacer. We compared the sequence and RNA secondary structure of the psbA 3' UTR across gymnosperms and found consensus motifs corresponding to the stem portions of the RNA stem-loop structures and a consensus TGGATTGTTATGT box. The psbA-trnH spacer is highly variable in length and composition. Tandem repeats that form stem?loop structures were detected in both the psbA 3' UTR and the psbA-trnH spacer. The presence of promoters and stem?loop structures in the psbA-trnH spacer and high sequence variation in this region suggest that psbA and trnH in some gymnosperms are independently transcribed. A comparison of chloroplast UTRs across gymnosperms offer clues to the identity of putative regulatory elements and information on selective constraints imposed on the chloroplast non-coding regions. The present study should inspire researchers to explore the full potential of the psbA-trnH non-coding sequence and to further stimulate its application in a broader spectrum of studies, not limited to phylogenetics and DNA barcoding.

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2 Journal of Applied Genetics

1 2010

1 2002

1 Bartoszewski G.

1 Bohanec B.

1 Chen S. L.

1 Hao D. C.

1 Havey M. J.

1 Lilly J. W.

1 Malepszy S.

1 Xiao P. G.

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Cucumber: A model angiosperm for mitochondrial transformation?

Sequence characteristics and divergent evolution of the chloroplast psbA-trnH noncoding region in gymnosperms