ScienceDaily (Mar. 25, 2010) — A reliable method for producing plants that carry genetic material from only one of their parents has been discovered by plant biologists at UC Davis. The technique, to be published March 25 in the journal Nature, could dramatically speed up the breeding of crop plants for desirable traits.
Researchers have developed a new method for producing plants that carry genetic material from only one of their parents. (Credit: iStockphoto)
"We were doing completely 'blue skies' research, and we discovered something that is immediately useful," said Simon Chan, assistant professor of plant biology at UC Davis and co-author on the paper.
Like most organisms that reproduce through sex, plants have paired chromosomes, with each parent contributing one chromosome to each pair. Plants and animals with paired chromosomes are called diploid. Their eggs and sperm are haploid, containing only one chromosome from each pair.
Plant breeders want to produce plants that are homozygous -- that carry the same trait on both chromosomes. When such plants are bred, they will pass the trait, such as pest resistance, fruit flavor or drought tolerance, to all of their offspring. But to achieve this, plants usually have to be inbred for several generations to make a plant that will "breed true."
The idea of making a haploid plant with chromosomes from only one parent has been around for decades, Chan said. Haploid plants are immediately homozygous, because they contain only one version of every gene. This produces true-breeding lines instantly, cutting out generations of inbreeding.
Existing techniques to make haploid plants are complicated, require expensive tissue culture and finicky growing conditions for different varieties, and only work with some crop species or varieties. The new method discovered by Chan and postdoctoral scholar Ravi Maruthachalam should work in any plant and does not require tissue culture.
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Nature 464, 615-618 (25 March 2010) | doi:10.1038/nature08842; Received 29 November 2009; Accepted 13 January 2010
Maruthachalam Ravi1 & Simon W. L. Chan1
Department of Plant Biology, University of California, Davis, Davis, California 95616, USA
Correspondence to: Simon W. L. Chan1 Correspondence and requests for materials should be addressed to S.W.L.C. (Email: srchan@ucdavis.edu).
Abstract
Production of haploid plants that inherit chromosomes from only one parent can greatly accelerate plant breeding1, 2, 3. Haploids generated from a heterozygous individual and converted to diploid create instant homozygous lines, bypassing generations of inbreeding. Two methods are generally used to produce haploids. First, cultured gametophyte cells may be regenerated into haploid plants4, but many species and genotypes are recalcitrant to this process2, 5. Second, haploids can be induced from rare interspecific crosses, in which one parental genome is eliminated after fertilization6, 7, 8, 9, 10, 11. The molecular basis for genome elimination is not understood, but one theory posits that centromeres from the two parent species interact unequally with the mitotic spindle, causing selective chromosome loss12, 13, 14. Here we show that haploid Arabidopsis thaliana plants can be easily generated through seeds by manipulating a single centromere protein, the centromere-specific histone CENH3 (called CENP-A in human). When cenh3 null mutants expressing altered CENH3 proteins are crossed to wild type, chromosomes from the mutant are eliminated, producing haploid progeny. Haploids are spontaneously converted into fertile diploids through meiotic non-reduction, allowing their genotype to be perpetuated. Maternal and paternal haploids can be generated through reciprocal crosses. We have also exploited centromere-mediated genome elimination to convert a natural tetraploid Arabidopsisinto a diploid, reducing its ploidy to simplify breeding. As CENH3 is universal in eukaryotes, our method may be extended to produce haploids in any plant species.
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