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 The group is focused on investigation of the molecular mechanisms for plant stress resistance. Our recent works include the structure and functional analysis of water channel proteins, investigation of the difference between lowland rice and upland rice in drought resistance and osmotic regulation, and comparative proteomic analysis of rice and Arabidopsis in response to abiotic stress.
Principal Investigator: Dr. Wei-Ning Sun, Research Associate. Email: wnsun@sibs.ac.cn
Staff: Jing Pan, Ting Bi, Research Interns
Graduate Students: Wei Huang; Shan-Shan Shi; Xiao-Jing Wang; Zhi-Lei Mao
Graduated Students: Min-Hua Zhang, 2000 (PhD); Guo-Wei Li, 2002 (PhD)
Characterization of OsPIP2;7, a Water Channel Protein in Rice
 Low temperature is one of the major stresses that limit the productivity and geographical distribution of many crops. It suppresses water transport and causes water deficit in leaves as a result of imbalance between water transport and transpiration. Plant aquaporins are believed to play an important role in maintaining cellular water homeostasis.
OsPIP2;7 was up-regulated in roots but down-regulated in shoots at the early stage of chilling stress. Cloning and expression of OsPIP2;7 in Xenopus oocytes system proved that it is an functional aquaporin with high water transport activity. We performed in situ hybridization to investigate the detailed spatial expression pattern of OsPIP2;7. OsPIP2;7 was localized mainly in mesophyll cells of leaves. In roots it was detected in the vascular tissues, epidermis cells and exodermis cells at the elongation zone, as well as in the epidermis cells, exodermis cells and root hair at the maturation zone.
Yeast cells overexpressing OsPIP2;7 showed a higher survival rate after freeze-thaw stress. Compare to the wild type cells, the survival rate of OsPIP2;7 overexpressing cells were increased from 0.201 to 1.639% and from 0.004 to 0.326% after one or two freeze-thaw cycles, respectively. We speculated that OsPIP2;7 was involved in the rapid water transport from the intracellular to the extracellular space of yeast cells, which might help to reduce intracellular ice crystal formation and the injury to the yeast cell membrane.
The cold stress tolerance of the OsPIP2;7 overexpressing rice was also assayed. During chilling stress, the leaves of both overexpressing and control rice were slightly wilted. However, the relative electrical conductivity, a key parameter of stress injury, of the overexpressing rice was lower than that of the control plants, suggesting that overexpressing increased the tolerance of rice to chilling stress. The moisture loss of the overexpressing and control plants under the chilling conditions was higher than that under normal conditions. We speculated that the transgenic plant with overexpression of OsPIP2;7 both in roots and in leaf mesophyll cells enhanced the ability for water uptake and rapid transport from roots to the aerial parts, which was reflected as a cumulative transpiration increase under normal conditions. These results indicated that OsPIP2;7 was involved in rapid water transport and maintenance of the water balance in cells, but could not avoid or repair the membrane damage caused during the chilling conditions.
Major Publications:
Li GW, Zhang MH, Cai WM, Sun WN and Su WA. (2008) Characterization of OsPIP2;7, a water channel protein in rice. Plant Cell Physiol. 49: 1851-1858. Yu CL, Yan SP, Wang CC, Hu HT, Sun WN, Yan CQ, Chen JP and Yang, L. (2008) Pathogenesis-related proteins in somatic hybrid rice induced by bacterial blight. Phytochemistry 69: 1989-1996.
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