Multicellular living organisms and unmodified parts thereof and – Method of introducing a polynucleotide molecule into or... – The polynucleotide alters plant part growth
Reexamination Certificate
2000-02-25
2004-02-17
Mehta, Ashwin (Department: 1638)
Multicellular living organisms and unmodified parts thereof and
Method of introducing a polynucleotide molecule into or...
The polynucleotide alters plant part growth
C435S320100, C435S468000, C536S023600, C800S298000
Reexamination Certificate
active
06693228
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the control of the time of flowering in plants by genetic engineering. Specifically, this invention relates to the control of the timing of flowering by manipulation of the activity of the FLOWERING LOCUS C (FLC) family of genes.
BACKGROUND OF THE INVENTION
The transition of growing plantlets from vegetative growth to flowering is the major developmental switch in the plant life cycle. The timing of flower initiation is critical for the reproductive success of wild plants, and most plant species have evolved systems to precisely regulate flowering time. These systems monitor both environmental cues and the developmental state of the plant to control flowering.
Two commonly monitored environmental cues are photoperiod and temperature. In the photoperiod-responsive plants so examined, daylength is perceived in leaves and flowering signals appear to be translocated from leaves to meristems (Zeevaart,
Light and the Flowering Process
, Process, eds., D. Vince-Prue, B. Thomas and K. E. Cockshull, 137-142, Academic Press, Orlando, 1984.). Exposure to cold temperatures promotes flowering by a process known as vernalization. Vernalization affects meristems directly, perhaps by causing them to become competent to perceive flowering signals (Lang,
Encyclopedia of plant Physiology
, ed., W. Ruhland, 15 (Part 1), 1371-1536, Springer-Verlag, Berlin, 1965). Other environmental cues that can affect flowering include light quality and nutritional status.
The developmental state of the plant can also influence flowering time. Most species go through a juvenile phase during which flowering is suppressed, and eventually undergo a transition to an adult phase in which the plant is competent to flower (Poethig,
Science
, 250, 923-930, 1990). This “phase change” permits the plant to reach a proper size for productive flowering. In the flowering literature, the developmental flowering pathways are often referred to as autonomous to indicate that they do not involve the sensing of environmental variables. However, it is unlikely that autonomous and environmental pathways are entirely distinct. For example, day-neutral species of tobacco flower after producing a specific number of nodes and thus could be classified as flowering entirely through an autonomous pathway, but grafting studies indicate that day-neutral and photoperiod-responsive tobacco species respond to similar translocatable flowering signals (Lang et al.,
Proc. Natl. Acad Sci., USA
, 74, 2412-2416, 1977; McDaniel et al.,
Plant J
., 9, 55-61, 1996). Thus aspects of the underlying biochemistry of these pathways appear to be conserved. Genetic analyses in several species has identified genes that affect the timing of flowering. The most extensive genetic analysis of flowering-time genes has been performed in
Arabidopsis thaliana
. In Arabidopsis, flowering-time genes have been identified by two approaches. One approach has been to induce mutations that affect flowering time in early-flowering varieties. Such mutations can cause either late-flowering or even earlier flowering. Late-flowering mutations identify genes whose wild-type role is to promote flowering and early-flowering mutations identify inhibitory ones. Studies in Arabidopsis have identified over 20 loci for which mutations specifically affect flowering time and several other loci that affect flowering time as well as other aspects of development (e.g., det2, cop1, ga1 and phyB) (Koornneef et al.,
Ann. Rev. Plant Physiol., Plant Mol. Biol
., 49, 345-370, 1998; Weigel,
Ann. Rev. Genetics
, 29, 19-39, 1995).
Another approach to identify flowering-time genes is to determine the genetic basis of naturally occurring variation in flowering time. Although the varieties of Arabidopsis most commonly used in the laboratory are early-flowering, most varieties are late-flowering. Late-flowering varieties differ from early-flowering ones in that the late-flowering varieties contain dominant alelles at two loci, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) that suppress flowering (Sanda et al.,
Plant Physiol
., 111, 641-645, 1996; Lee et al.,
Plant Journal
, 6, 903-909, 1994; Clarke et al.,
Mol. Gen. Genet
., 242, 81-89, 1994; Koornneef et al.,
Plant Journal
, 6, 911-919, 1994).
Physiological analyses of flowering-time mutants and naturally occurring variation in flowering time indicate that flowering is controlled by multiple pathways in Arabidopsis (Koomneef et al.,
Ann. Rev. Plant Physiol., Plant Mol. Biol
., 49, 345-370, 1998). One group of late-flowering mutants (fca, fpa, fve, fy, ld) and plants containing the late-flowering FLC and FRI alleles are delayed in flowering in inductive (long-day) conditions and are even more severely delayed in short days. Vernalization of these late-flowering lines can suppress the late-flowering phenotype. Another group of late-flowering mutants (co, fd, fe, fha, ft, fwa, gi) exhibit a slight or no difference in flowering time when grown in short days compared to long days. Furthermore, this group shows little or no response to vernalization. Double mutants within a group do not flower significantly later than either single-mutant parent, whereas double mutants containing a mutation in each group flower later than the single-mutant parents (Koomneefet al., Genetics, 148, 885-92, 1998). Thus, there appears to be parallel flowering pathways that mediate the flowering response to environmental and developmental cues. A photoperiod pathway promotes flowering in long days. A pathway referred to in the literature as autonomous (because the photoperiod response is not affected by mutations in this pathway) appears to control the age, or more specifically the developmental stage, at which plants are competent to flower. Recent support of the developmental role of this pathway is the demonstration that autonomous pathway mutants exhibit changes such as alterations of trichome patterns that indicate such mutant plants are delayed in the juvenile to adult transition (Telfer et al.,
Development
, 124, 645-654, 1997).
Blocks to the autonomous pathway due to mutant fca, fpa, fve, fy, and ld alleles or to the presence of dominant late-flowering FLC and FRI alleles can be bypassed by vernalization (Koornneef et al.,
Ann. Rev. Plant Physiol., Plant Mol. Biol
., 49, 345-370, 1998). Thus FLC and FRI can be regarded as genes that create a requirement for vernalization. Other species, particularly Brassicas, appear to have the same “circuitry” as Arabidopsis. This similarity has been most thoroughly analyzed for the relationship between dominant suppressors of flowering and vernalization in Brassicas. The major difference between annual and biennial cultivars of oilseed
Brassica napus
and
B. rapa
is conferred by genes controlling vernalization-responsive flowering time (Osborn et al., Genetics Society of America, 146, 1123-1129, 1997). By comparing quantitative trait loci (QTLs) in segregating populations of annual X biennial varieties of
B. rapa
and
B. napus
, it was shown that the 2 major QTLs that confer vernalization-responsive late flowering in
B. napus
and
B. rapa
are likely to be the same (Osborn et al., Genetics Society of America, 146, 1123-1129, 1997). In
B. rapa
the two flowering-time QTLs were separated in recombinant inbred populations and the QTL with the greatest effect on flowering time was VFR2 (vernalization-responsive flowering time in rapa 2). Furthermore, VFR2 appears to correspond to FLC from Arabidopsis: VFR2 was mapped at high resolution using hybridization probes that permit a comparison of Arabidopsis and Brassicas after introgression of the late allele into the early-flowering annual variety, and only a probe corresponding to FLC detected no recombination events with VFR2 (<0.44 cm) indicating that VFR2 is an FLC homolog.
The timing of flowering is of great importance in agriculture and horticulture. In horticultural crops the product is often the flowers. In food, feed crops, or fiber crops, such as the cereals rice, wheat, maize, barley, and oats, and dicots such as soybe
Amasino Richard Mark
Michaels Scott Daniel
Schomburg Fritz Michael
Scortecci Katia
Sung Si-Bum
Mehta Ashwin
Quarles & Brady LLP
Wisconsin Alumni Research Foundation
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