Multicellular living organisms and unmodified parts thereof and – Method of using a plant or plant part in a breeding process...
Reexamination Certificate
2000-05-23
2004-06-15
Nelson, Amy J. (Department: 1638)
Multicellular living organisms and unmodified parts thereof and
Method of using a plant or plant part in a breeding process...
C800S269000
Reexamination Certificate
active
06750376
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods for producing plants that genetically clone themselves through their own seed (gametophytic apomicts) from plants that normally reproduce sexually. More particularly, the invention relates to processes that include (a) selection of two or more sexual lines that express reproductive phenotypes divergent from each other, which may in some cases require plant breeding and selection to obtain sufficient degrees of divergence, (b) hybridization among plants divergent in reproductive phenotype, and (c) amphiploidization (doubling of chromosomes) either before or after hybridization.
It is likely that apomixis has a greater potential for increasing yields of food, feed, and fiber than any other plant mechanism. Apomixis occurs in about 0.3% of flowering plant species. The present patent application describes methods for making sexual plants apomictic without crossing them to wild apomictic relatives or using mutagenic procedures, both of which have been attempted but with disappointing results. The procedures described herein mimic how apomixis evolved in nature (J. G. Carman, Asynchronous Expression of Duplicate Genes in Angiosperms May Cause Apomixis, Bispory, Tetraspory, and Polyembryony, 61 Biol. J. Linnean Soc. 51-94 (1997) (incorporated herein by reference; hereinafter, “Linnean”), and enable persons skilled in the art of plant breeding and genetics to convert inbred crops, including wheat, barley, and rice, into apomictic hybrid crops with potential yield increases of 10 to 30% over currently used inbred varieties. Crops currently used as hybrids, such as maize, may also be made apomictic. Apomictic hybrids of either inbred or typically hybrid crops will behave as hybrids only in terms of their superior yields. The seed of apomictic hybrids are genetic clones of the mother hybrid, i.e. genetic segregation does not occur. Thus, farmers could use a small fraction of their harvest for seed and expect high yields and uniformity year after year. This would allow hybrids, the seed of which is typically very expensive, to be used in impoverished nations for the first time, which could contribute substantially to another “green revolution”.
Gregor Mendel conducted, unknowingly, the first genetic experiments with gametophytic apomicts (plants that produce seed asexually). He reported the successful crossing of different Hieracium lines but commented on the extreme difficulty of preventing self fertilization. What he thought was high frequency accidental selfing (in his facultatively-apomictic Hieracium lines) was actually high frequency apomictic seed formation. To add to his frustration, Mendel failed to observe segregation among the F
2
s of the few F
1
s he managed to produce. His F
2
s were actually apomictic clones of his F
1
s, and they invariably expressed their respective F
1
, phenotypes (S. E. Asker & L. Jerling, Apomixis in Plants (CRC Press, 1992) (hereby incorporated by reference; hereinafter, “Asker & Jerling”).
Several thousand species of Hieraclum had been described by the time Mendel hybridized members of this agamic complex. This pronounced polymorphy, and that observed in other agamic complexes (Antennaria, Erigeron, Taraxacum, Potentilla), coupled with Mendel's results in producing new polymorphs by crossing facultative apomicts, led early geneticists to conclude that hybridization in agamic complexes is a major mechanism of speciation. Evidence for this conclusion is replete, e.g. in Amelanchier and Crataequs (C. S. Campbell & T. A. Dickinson, Apomixis, Patterns of Morphological Variation, and Species Concepts in Subfam. Maloideae (Rosaceae), 15 Systematic Bot. 124-25 (1990) (incorporated herein by reference), in Antennaria (Bayer et al., Phylogenetic Inferences in Antennaria (Asteraceac: Gnaphalieae) Based on Sequences from the Nuclear Ribosomal DNA Internal Transcribed Spacers (ITS), 83 Amer. J. Bat. 516-527 (1996) (incorporated herein by reference), in numerous agamic grass complexes (E. A. Kellogg, variation and Species Limits in Agamospermous Grasses, 15 Systematic Bot. 112-23 (1990) (incorporated herein by reference), in Rubus (Nybom, Evaluation of Interspecific Crossing Experiments in Facultatively Apozmictic Blackberries (Rubus Subgen. Rubus). Using DNA Fingerprinting, 122 Hereditas 57-65 (1995) (incorporated herein by reference), in Taraxacum (Richards, The origin of Taxaxacum agamospecies, 66 Biol. J. Linnean Soc. 189-211 (1973) (incorporated herein by reference), and others. In contrast, two conflicting opinions soon developed among early geneticists regarding the role of hybridization in the origins of apomixis. Strausburger, Zeitpunkt der Bestimmung des Geschlechtes, Apogamie, Parthenogenesis und Reduktionsteilung, 7 Hist. Beitr. 1-124 (1909) (incorporated herein by reference), Ostenfeld, Experiments on the Origin of Species in the Genus Hieraci (Apogamy and Hybridism), 11 New Phytol. 347-54 (1912) (incorporated herein by reference), and Holmgren, Zytologische Studien uber die Fortpflanzung bei den Gattungen Erigeron und Eupatorium, 59 Kgl. Sven Vetenskapsakad. Ak. Handl. No. 7, 1-118 (1919) (incorporated herein by reference) believed apomixis is controlled by genetic factors (genes) specific to apomixis and is not a consequence of hybridization. In contrast, A. Ernst, Bastardierung als Ursache der Apogamie im Pflanzenreich, Fischer, Jena (1918) (incorporated herein by reference), believed that the cytological anomalies of reproduction responsible for apomixis are extensions of the genomic disturbances observed in wide hybrids.
Ernst amassed much evidence to support his hybridization hypothesis, which included the facts What apomicts have high chromosome numbers (they are generally polyploid), that agamic complexes are highly polymorphic, and that the sex cells of apomicts often degenerate in a manner observed in interspecific hybrids. A major tenet of Ernst's hypothesis, and the one which soon caused its widespread dismissal (and continues to cause its legitimate dismissal today), was that hybrids form a continuum from fully functional sexual reproduction, to apomixis, and finally to vegetative reproduction. Where a hybrid fit on the continuum depended on how closely related the parent species are, e.g. if the parents are closely related, the hybrid will reproduce sexually, if the parents are moderately related, the hybrids may tend to be apomictic, if the parents are distantly related, the hybrids may tend to reproduce by vegetative propagation. Thus, according to Ernst, apomixis arises only in wide hybrids. Ernst did not identify mechanisms to support a hybrid origin for apomixis other than the wideness of the cross.
Ernst's hypothesis received support in the 1920s and 1930s (Harrison, The Inheritance of Melanism in Hybrids Between Continental
Tephrosia crepuscularia
and
Britisht bistortata
, with Some Remarks on the Origin of Parthenogenesis in Interspecific Crosses, 9 Genetika 4467 (1927) (incorporated herein by reference); G. L. Stebbins, Cytology of Antennaria. II. Parthenogenetic Species, 94 Bot. Gaz. 322-45 (1932) (incorporated herein by reference)), but most geneticists had rejected it by the time Ake Gustafsson published his comprehensive treatise, A Gustafsson, Apomixis in Higher Plants, I. The Mechanism of Apomixis, 42 Lunds Universitets Arsskrift 1-67 (1946); A Gustafsson, Apomixis in Higher Plants, II. The Causal Aspect of Apomixis, 43 Lunds Universitets Arsskrift 69-179, (1947); A Gustafsson, Apomixis in Higher Plants, III. Biotype and Species Formation, 43 Lunds Universitets Arsskrift 181-370 (1947) (incorporated herein by reference). In this treatise, Gustafsson concluded; “In no case is it proved that hybridization itself has been able to produce apomixis. On the contrary, it is certain that the apomictic method of reproduction has in many cases arisen within a species population.” The fact that some apomicts are autopolyploid, which was well documented by 1946, legitimately squelched any perceived requirement for wide hybridization. Hence, Ernst's
Kubelik Anne
Nelson Amy J.
Utah State University
Winston & Strawn LLP
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