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
2001-04-04
2004-08-31
Bui, Phuong T. (Department: 1638)
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, C800S287000, C800S320300, C800S320100, C800S314000, C800S320000, C800S312000, C536S023100, C536S023600, C435S320100, C435S468000
Reexamination Certificate
active
06784343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to proteins and nucleic acids related to salt tolerance in plants.
2. Description of the Background
In
Arabidopsis thaliana
, the Salt Overly Sensitive 2 (SOS2) gene is required for intracellular Na
+
and K
+
homeostasis. Mutations in SOS2 cause Na
+
and K
+
imbalance and render plants more sensitive toward growth inhibition by high Na
+
and low K
+
environments. We isolated the SOS2 gene through positional cloning. SOS2 is predicted to encode a serine/threonine type protein kinase with an N-terminal catalytic domain similar to that of the yeast SNF1 kinase. Sequence analyses of sos2 mutant alleles reveal that both the N-terminal catalytic domain and the C-terminal regulatory domain of SOS2 are functionally essential. The steady-state level of SOS2 transcript is up-regulated by salt stress in the root. Autophosphorylation assays show that SOS2 is an active protein kinase. In the recessive sos2-5 allele, a conserved glycine residue in the kinase catalytic domain is changed to glutamate. This mutation abolishes SOS2 autophosphorylation, indicating that SOS2 protein kinase activity is required for salt tolerance.
Control of intracellular ion homeostasis is essential for all cellular organisms. Most cells maintain relatively high K
+
and low Na
+
concentrations in the cytosol. In plants. this is achieved through coordinated regulation of transporters for H
+
, K
+
, and Na
+
. At the plasma membrane, a family of P-type H
+
-ATPases serves as the primary pump that generates a protonmotive force driving the active transport of other solutes, including K
+
and Na
+
(1). Several plant K
+
channels and transporters have been molecularly characterized. The inward rectifying K
+
channel AKT1 is essential for root K
+
uptake in
Arabidopsis thaliana
(2, 3). Expression characteristics indicate that the KAT1 channel is involved in K
+
influx in Arabidopsis guard cells (4, 5). Recently, an outward rectifying K
+
channel has been shown to be essential for unloading K
+
into the Arabidopsis root xylem (6). The wheat HKT1 gene product functions as a high-affinity K
+
transporter (7). In addition, a family of KUP genes exists in Arabidopsis. At least one of them, KUP1, encodes a protein that can function as a dual-affinity K
+
transporter (8, 9). Na
+
enters plant cells passively, presumably through K
+
transport systems (10), Unlike animals or fungi. plants do not seem to possess Na
+
/K
+
-ATPases or Na
+
-ATPases. Na
+
efflux s achieved through the activities of Na
+
/H
+
antiporters on the plasma membrane. Much of the Na
+
that enters the cell is compartmentalized into the vacuole through the action of vacuolar Na
+
/H
+
antiporters (11, 12). The driving force for the vacuolar transporters is the protonmotive force created by vacuolar V-type H
+
-ATPases and the H
+
-pyrophosphatase (1, 13). Although there has been great progress in the characterization of K
+
and Na
+
transporters in plants, little is currently known about their regulation.
In the trophic chain, plant roots play pivotal roles by taking up mineral nutrients from soil solutions. Plant roots experience constant fluctuations in soil environments. A frequent variant in the soil solution is Na
+
concentration (14). Na
+
is not an essential ion for most plants. In fact, the growth of the majority of plants, glycophytes, is inhibited by the presence of high concentrations of soil Na
+
. External Na
+
causes K
+
deficiency by inhibiting K
+
uptake into plant cells (15). Na
+
accumulation within the cell is toxic to many cytosolic enzymes. In contrast, many cellular enzymes are activated by K
+
, which is the most abundant cation in the cytoplasm. Certain cytoplasmic enzymes arc especially prone to Na
+
inhibition when K
+
concentration is reduced (16). Therefore, maintaining intracellular K
+
and homeostasis to preserve a high K
+
/Na
+
ratio is important for all cells and especially critical for plant cells.
A family of
Arabidopsis sos
(salt overly sensitive) mutants defective in the regulation of intracellular Na
+
and K
+
homeostasis was recently characterized (15, 17, 18). The sos mutants are specifically hypersensitive to inhibition by high concentrations of external Na
+
or Li
−
(17, 18). In response to high Na
+
challenge, the sos2 and sos3 mutants accumulate more Na
+
and retain less K
+
than wild-type plants (18). The mutants are also unable to grow when the external K
+
concentration is very low (17, 18). These phenotypes suggest that the mutant plants are defective in the regulation of K
+
and Na
+
transport (18). The SOS3 gene was recently cloned and shown to encode an EF hand-type calcium-binding protein that shares significant sequence similarities with animal neuronal calcium sensors and the yeast calcineurin B subunit (19). In yeast, calcineurin is a central component in the signaling pathway that regulates Na
+
and K
−
homeostasis (20, 21). Loss-of-function mutations in calcineurin B cause increased sensitivity of yeast cells to Na
+
or Li
+
stress.
Because of limited water supplies and the widespread use of irrigation, the soils of many cultivated areas have become increasingly salinized. In particular, modern agricultural practices such as irrigation impart increasing salt concentrations when the available irrigation water evaporates and leaves previously dissolved salts behind. As a result, the development of salt tolerant cultivars of agronomically important crops has become important in many parts of the world. For example, in salty soil found in areas such as Southern California, Arizona, New Mexico and Texas.
Dissolved salts in the soil increase the osmotic pressure of the solution in the soil and tend to decrease the rate at which water from the soil will enter the roots. If the solution in the soil becomes too saturated with dissolved salts, the water may actually be withdrawn from the plant roots. Thus the plants slowly starve though the supply of water and dissolved nutrients may be more than ample. Also, elements such as sodium are known to be toxic to plants when they are taken up by the plants.
Salt tolerant plants can facilitate use of marginal areas for crop production, or allow a wider range of sources of irrigation water. Traditional plant breeding methods have, thus far, not yielded substantial improvements in salt tolerance and growth of crop plants. In addition, such methods require long term selection and testing before new cultivars can be identified.
Accordingly, there is a need to increase salt tolerance in plants, particularly those plants which are advantageously useful as agricultural crops.
SUMMARY OF THE INVENTION
We report here the positional cloning of the SOS2 locus. SOS2 is predicted to encode a serine/threonine type protein kinase with an N-terminal catalytic domain highly similar to those of yeast SNF1 and mammalian AMPK kinases. Sequence analyses of several sos2 mutant alleles point to a functional requirement of both the N-terminal catalytic domain and the C-terminal regulatory domain of SOS2. SOS2 is expressed in both the root and shoot. In the root, SOS2 mRNA is up-regulated by salt stress. Autophosphorylation assays demonstrate that SOS2 is an active protein kinase. Furthermore, a mutation that abolishes SOS2 autophosphorylation renders plants hypersensitive to salt stress, indicating that SOS2 protein kinase activity is necessary for salt tolerance. This demonstrates that a protein kinase is essential for intracellular Na
+
and K
+
homeostasis and plant salt tolerance.
Thus, the present invention provides an isolated polynucleotide which encodes a protein comprising the amino acid sequence in SEQ ID NO:2.
In a
Halfter Ursula
Ishitani Manabu
Kim Cheol-Soo
Liu Jiping
Zhu Jian-Kang
Baum Stuart F.
Bui Phuong T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Arizona Board of Regents
LandOfFree
Proteins and DNA related to salt tolerance in plants does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Proteins and DNA related to salt tolerance in plants, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Proteins and DNA related to salt tolerance in plants will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3334399