Progress 08/01/07 to 07/31/10
Outputs
OUTPUTS: The project grant supported activities in Luan lab where a systematic effort was made to identify the functional network of salt tolerance in rice. A critical finding is that a HKT family transporter functions as a calcium-permeable channel, breaking the dogma that HKT transporters transport only potassium or sodium. This is significant in understanding the calcium-mediated signaling systems in plants. PARTICIPANTS: Dr. Wenzhi Lan was the postdoctoral fellow working on this project. Dr. Suomin Wang, a visting professor, also participated in this study. Several students from our collaborating group in the Chinese Academy of Sciences in Shanghai also worked on this project. This project thus provide training for these students and visiting scientists. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The project funding supported activities of one postdoctoral fellow whose expertise in patch-clamp technique contributed critically to the discovery of calcium-permeable channel in the HKT family.
Publications
- Lan WZ, Wang W, Wang SM, Li LG, Buchanan BB, Lin HX, Gao JP, Luan S. (2010) A rice high-affinity potassium transporter (HKT) conceals a calcium-permeable cation channel. Proc. Natl. Acad. Sci. USA. 107(15):7089-94.
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Progress 08/01/08 to 07/31/09
Outputs
OUTPUTS: Compared to a single AtHKT1 gene in Arabidopsis, the monocot crop model rice contains 9 HKT-like genes, a striking departure from the dicot model. Available data suggest that various members within the rice HKT family may belong to either group 1 or group 2 HKTs. A recent study identified OsHKT1;5 gene as a critical quantitative trait locus for salt tolerance in rice because it functions as a Na-specific transporter like AtHKT1 and prevents Na-accumulation in shoots. A second HKT gene in rice (OsHKT2;1) was shown to uptake Na to maintain cell growth under low-K condition. Therefore, a diverse function profile is predicted for each different member of the HKT family in rice. To address the functions of all HKT proteins and establish the salt transport network in rice, we isolated and analyzed transposon-tagged mutants in OsHKT genes and determined the transport properties of each OsHKT. This study provides experimental evidence that at least some of the Ktr/TRK/HKT-type transport proteins are bona fide ion channels. PARTICIPANTS: Dr. Wenzhi Lan has been working on this project, in collaboration with Dr. HOngxuan Lin's group in Shanghai, Chinese Academy of Science. TARGET AUDIENCES: Progress in the project has advanced our knowledge on plant salt tolerance and signal transduction. This will enhance our ability of engineering crops with higher tolerance to salt and other stress conditions. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Although plant HKT proteins are related to a high-affinity K-transporter in bacteria and fungi, available data indicate that they function as Na-uniporters or Na-K symporters in plants, implying the structural and functional diversity acquired during evolution of green plants. Interestingly, even among flowering plants, HKT proteins appear to evolve rapidly with large difference in dicot model Arabidopsis and monocot model rice. While Arabidopsis genome contains only a single HKT gene, rice genome contains up to 9 HKT genes (depending on rice species), representing a significant variation concerning the structure and importance of HKT proteins in different plants species. Despite more members, rice HKT proteins are highly similar in their amino acid sequences suggesting similar structure and functions. Indeed studies so far identified several rice HKT proteins as Na-uniporters or Na-K symporters, as expected from earlier work on AtHKT1;1 and wheat HKT1. Our study reveals a distinct feature of several OsHKTs, significantly expanding our understanding on the functional diversity of plant HKT proteins. Some proteins, such as the cystic fibrosis transmembrane regulator and dopamine transporters, whose structure belongs to transporter family, exhibit channel-like features. HKT proteins may thus contribute to the regulation of signal transduction related to ionic fluxes.
Publications
- No publications reported this period
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Progress 08/01/07 to 07/31/08
Outputs
OUTPUTS: Our recent study (Nature Genetics 37, 1141) achieved a breakthrough in understanding the molecular nature of salt tolerance in rice. In this study, we showed that a major QTL for rice salt tolerance encodes a sodium transporter belonging to the HKT family. A striking difference between rice and Arabidopsis is revealed: the rice HKT family has at least eight distinct members versus only one in Arabidopsis. Furthermore, different rice HKT members are expressed in various tissues and transport different ions, suggesting that they function in different processes in planta including Na+ uptake from soil, long distance translocation between roots and shoots, and intracellular compartmentalization. Therefore HKT family transporters constitute a "salt transport network" in rice and the functional analysis of this network will significantly improve our understanding on the "entire molecular network" for salt tolerance in rice plants. Functional integration of the multigene HKT family in rice will present a new conceptual framework on salt homeostasis beyond the paradigm learnt in the Arabidopsis model (with a single gene). Because EST analysis revealed multiple HKT genes in other plant species as well, it is likely that study on multigene family of rice HKTs will provide a more universal paradigm for salt tolerance in plants beyond cereals. Following our recent work that demonstrates a salt tolerance determinant being a member of HKT family in rice, we are continuing the functional analysis of this and other HKT members in rice to establish how HKT family proteins function in vivo to contribute to the ionic homeostasis and salt tolerance in the cereal model. PARTICIPANTS: Two people work on this project, Sheng Luan as PI and Wenzhi Lan as postdoctoral fellow. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Rice is a staple food crop for over half of the world population and serves as a model system for other cereals. Salinity is a major stress factor that severely reduces crop yield worldwide. Attempts to improve salt tolerance of crops through conventional breeding have not been very successful due to the complexity of the trait: Tolerance trait is often associated with quantitative trait loci (QTLs) that have been challenging to isolate. Additionally, Na+ stress is closely tied with K+-nutrition. In particular, some HKT members have been shown to transport both Na+ and K+. Therefore studying HKT network in rice will contribute to the understanding of not only salt tolerance but also K-nutrition stress. The project will thus address two priority areas in this USDA program: 1) Water stress (drought, salt, and flooding) and 3) Nutrition stress (Na-K homeostasis)."
Publications
- No publications reported this period
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