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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

An Insight into the Molecular Basis of Salt Tolerance of L-myo-Inositol 1-P Synthase (PcINO1) from Porteresia coarctata (Roxb.) Tateoka, a Halophytic Wild Rice¹

Plant Molecular and Cellular Genetics (K.G.D., S.M., L.G., A.L.M.), Bioinformatics Center (D.R.), and Department of Chemistry (K.P.D.), Bose Institute, Calcutta Improvement Trust Scheme-VIIM, Calcutta 700 054, India

The molecular basis of salt tolerance of L-myo-inositol 1-P synthase (MIPS; EC 5.5.1.4) from Porteresia coarctata (Roxb.) Tateoka (PcINO1, AF412340) earlier reported from this laboratory, has been analyzed by in vitro mutant and hybrid generation and subsequent biochemical and biophysical studies of the recombinant proteins. A 37-amino acid stretch between Trp-174 and Ser-210 has been confirmed as the salt-tolerance determinant domain in PcINO1 both by loss or gain of salt tolerance by either deletion or by addition to salt-sensitive MIPS(s) of Oryza (OsINO1) and Brassica juncea (BjINO1). This was further verified by growth analysis under salt environment of Schizosaccharomyces pombe transformed with the various gene constructs and studies on the differential behavior of mutant and wild proteins by Trp fluorescence, aggregation, and circular dichroism spectra in the presence of salt. 4,4'-Dianilino-1,1'-binaphthyl-5,5-disulfonic acid binding experiments revealed a lower hydrophobic surface on PcINO1 than OsINO1, contributed by this 37-amino acid stretch explaining the differential behavior of OsINO1 and PcINO1 both with respect to their enzymatic functions and thermodynamic stability in high salt environment. Detailed amino acid sequence comparison and modeling studies revealed the interposition of polar and charged residues and a well-connected hydrogen-bonding network formed by Ser and Thr in this stretch of PcINO1. On the contrary, hydrophobic residues clustered in two continuous stretches in the corresponding region of OsINO1 form a strong hydrophobic patch on the surface. It is conceivable that salt-tolerant MIPS proteins may be designed out of the salt-sensitive plant MIPS proteins by replacement of the corresponding amino acid stretch by the designated 37-amino acid stretch of PcINO1.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Arun Lahiri Majumder (lahiri{at}bic.boseinst.ernet.in).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.075150.

^* Corresponding author; e-mail lahiri{at}bic.boseinst.ernet.in; fax 91–33–2334–3886.

Received December 6, 2005; returned for revision January 5, 2006; accepted January 5, 2006.

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