Multicellular living organisms and unmodified parts thereof and – Plant – seedling – plant seed – or plant part – per se – Higher plant – seedling – plant seed – or plant part
Reexamination Certificate
1998-04-02
2001-05-08
Benzion, Gary (Department: 1649)
Multicellular living organisms and unmodified parts thereof and
Plant, seedling, plant seed, or plant part, per se
Higher plant, seedling, plant seed, or plant part
C800S278000, C800S295000, C435S419000, C435S468000, C435S320100, C536S023600, C536S024100
Reexamination Certificate
active
06229069
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for controlling the water content of a plant in order to provide a plant which is tolerant to water-related stress such as salt stress or drought stress.
Plants are continuously exposed to stress even under normal growing conditions. Such stress is caused by various factors such as salt, drought, high temperature, low temperature, strong light, air pollution, etc. From the viewpoint of agriculture, salt and drought stress cause the most serious problems. Salt stress is observed not only in areas which have a soil inherently rich in salt but also in irrigated farms. At present, more than 10% of cultivated land suffers from some degree of salt stress. To increase food production, it is desired to grow crop in land which has previously been regarded as uncultivatable.
Drought stress is caused by unseasonable weather and geographic location. In the United States, drought causes a fall in crop yield once every several years.
Therefore, it is important to find a plant which is tolerant to water-related stress.
In this regard, it is known that water channel proteins (hereinafter sometimes referred to simply as WCH proteins) seemingly have a role to play in “water flux in plants”.
These plant WCH proteins are classified into plasma membrane-located types and tonoplast-located types. Some reports have already published on the genes of these proteins.
In connection with the genes of plasma membrane-located WCH proteins, there have been reported, for example, the cloning of cDNA of a turgor responsible WCH protein derived from pea [Plant Molecular Biology 15, 11-26 (1990)]; the cloning of cDNA of a desiccation responsible WCH protein derived from
Arabidopsis thaliana
(Plant Cell Physiology 33, 217-224); WCH gene of
Arabidopsis thaliana
[The Plant Journal 6, 187-199 (1994)]; WCH gene of tomato [Plant Molecular Biology 24, 539-543 (1994)]; the introduction of an antisense gene into
Arabidopsis thaliana
to confirm its function in the water channel [The Plant Journal 7, 87-95 (1995)]; WCH gene of common ice plant (
Mesembryanthemum crystallinum
) [The plant Cell 7, 1129-1142 (1995)], etc. In addition, those derived from corn, rice, kohlrabi (
Brassica oleracea
), soybean, barley, etc. have been registered at gene data bases, etc.
In connection with the genes of tonoplast-located WCH proteins, there have been reported, for example, one derived from tobacco [Nucleic Acids Research 18, 7449 (1990)]; one derived from common bean [The Plant Cell 2, 525-532 (1990)]; one derived from
Arabidopsis thaliana
[Plant Physiology 99, 561-570 (1992)], etc. In addition, those of rice, barley, soybean, radish (
Raphanus sativa
), white clover (
Triforium repens
), alfalfa (
Medicago sativa
), etc. have been registered at gene data bases, etc.
As described above, it has been urgently required to provide a plant which is tolerant to water-related stress. One approach to obtain such a plant is directed to controlling the water content of the plant by, for example, gene manipulation. In general, it is considered that a plant which is tolerant to water-related stress can be obtained by increasing the water content of the plant, namely, enhancing the capability of the plant to obtain water.
To obtain a water-related stress-tolerant plant in the above-mentioned manner, WO 96/00789 and Nature 379 (22) 683-684 (1996) disclose a method for obtaining a plant tolerant to water-related stress by way of controlling the water content of the plant. The method comprises introducing the gene of an enzyme for trehalose biosynthesis into the plant, thereby to induce the synthesis and accumulation of trehalose in the plant, and to eliminate the loss in water content by way of the water-retaining effect of trehalose. The disclosure of these references is incorporated herein by reference.
However, this method suffers from various problems. Namely, a certain amount of carbon fixed by photosynthesis is consumed in this method, which is disadvantageous from the viewpoint of energy consumption. In addition, there is a risk that the accumulation of trehalose might exert adverse effects on the qualities of the product and the metabolic system of the plant.
On the other hand, it has been considered that the WCH proteins described above may participate in water flux in a plant. However, no one has suggested so far that the water content of a plant may be controlled by using these proteins.
SUMMARY OF THE INVENTION
The present invention, which has been accomplished under the above-mentioned circumstances, provides a method for controlling the water content of a plant by introducing a plant WCH protein gene into the plant and aims at thus obtaining a plant tolerant to water related stress.
The present invention further provides a plant which is produced by the above method and hence possesses a controlled water content.
The present invention further provides a plant which has an improved tolerance to drought stress and/or salt stress due to the controlled water content.
DETAILED DESCRIPTION
Now, the present invention will be described in greater detail.
The present invention is characterized in that a plant WCH protein gene is introduced into a plant to thereby control the water content of the plant thus transformed.
The plant WCH proteins to be used in the present invention includes plasma membrane-located WCH proteins and tonoplast-located ones. Although genes encoding proteins of both of these types may be used in the present invention, genes of WCH proteins which are located in plasma membrane are preferred.
As described above, there have been known genes encoding plasma membrane-located WCH proteins of various origins such as pea,
Arabidopsis thaliana
, tomato,
Mesembryanthemum crystallinum
, corn, rice, kohlrabi, soybean, barley, etc. These known genes may be used in the present invention. However, WCH protein genes to be used in the present invention are not limited thereto, provided that those of WCH proteins located in plasma membrane are preferred.
As a method of obtaining a gene of a plasma membrane-located WCH protein, the Examples hereinbelow will illustrate a method to obtain a gene from
Mesembryanthemum crystallinum
. Further, gene from other plants can be obtained by reference to the following literatures.
(1) Pea (
Pisum sativum
) [Plant Molecular Biology 15, 11-26 (1990)].
(2)
Arabidopsis thaliana
[Plant Cell Physiology 33, 217-224 (1992); Plant Molecular Biology 23, 1187-1198 (1993); The Plant Journal 6, 187-199 (1994)].
(3) Tomato [Plant Molecular Biology 24, 539-543 (1994)].
The gene encoding a plant WCH protein to be used in the present invention may be operatively introduced into a plant in such a manner that the genetic code will be translated either in the sense direction or in the antisense direction. In order to enhance the water-retaining capacity of the plant under water stress, it is preferred in the present invention that the gene is introduced into the plant in the sense direction. However, in certain cases, reduced water flux in plants is expected to be beneficial for them and hence, introduction of the gene in the antisense direction will be desired, depending on the strength, timing or kind of stress.
It is preferred in the present invention that the gene encoding a plant WCH protein, which is to be introduced into a plant in the sense direction, is one derived from a plant which is tolerant to salt stress or drought stress, still preferred is one derived from
Mesembryanthemum crystallinum.
When the gene is introduced into the plant in the antisense direction, on the other hand, it is preferred that the species of the plant to be transformed is as close as possible to the species from which the gene is obtained. It is still preferred that the gene is of the same species as the plant to be transformed. When the gene is introduced in the antisense direction, it is not always necessary to introduce the whole gene. Namely, su
Benzion Gary
Birch & Stewart Kolasch & Birch, LLP
Haas Thomas
Japan Tobacco Inc.
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