
@article {78101,
	title = {Homology modeling identifies crucial amino-acid residues that confer higher Na+ transport capacity of OcHKT1;5 from Oryza coarctata Roxb.},
	journal = {Plant Cell Physiol},
	year = {2020},
	month = {2020 May 07},
	abstract = {<p>HKT1;5 loci/alleles are important determinants of crop salinity tolerance. HKT1;5s encode plasmalemma-localized Na+-transporters, retrieving xylem Na+ into xylem parenchyma cells, reducing shoot Na+ accumulation. Allelic variation in rice OsHKT1;5 sequence in specific landraces (Nona Bokra OsHKT1;5-NB/Nipponbare OsHKT1;5-Ni) correlates with variation in salt tolerance. Oryza coarctata, a halophytic wild rice, grows in fluctuating salinity at the seawater-estuarine interface in Indian and Bangladeshi coastal regions. The distinct transport characteristics of the shoots and roots expressing O. coarctata OcHKT1;5 transporter, are reported vis-{\`a}-vis OsHKT1;5-Ni. Yeast sodium extrusion-deficient cells expressing\&nbsp;OcHKT1;5 are sensitive to increasing Na+ (10-100 mM). Electrophysiological measurements in Xenopus oocytes expressing O. coarctata or rice HKT1;5 transporters indicates that OcHKT1;5, like OsHKT1;5-Ni is a Na+-selective transporter, but displays 16-fold lower affinity for Na+ and 3.5-fold higher maximal conductance than OsHKT1;5-Ni. For Na+ concentrations greater than 10 mM, OcHKT1;5 conductance is higher than that of OsHKT1;5-Ni, indicating potential of OcHKT1;5 for increasing domesticated rice salt tolerance. Homology modeling/ simulation suggests that four key amino acid changes in OcHKT1;5 (in loops on the extracellular side; E239K, G207R, G214R, L363V), account for its lower affinity and higher Na+ conductance vis-{\`a}-vis OsHKT1;5-Ni. Of these, E239K in OcHKT1;5, confers lower affinity for Na+ transport, as evidenced by Na+ transport assays of reciprocal site directed mutants for both transporters (OcHKT1;5- K239E, OsHKT1;5-Ni- E270K) in Xenopus oocytes. Both transporters have analogous roles in xylem sap desalinization and differences in Na+ transport affinity/ conductance between the transporters is attributable to differences in xylem sap Na+ concentrations in both species.</p>
},
	issn = {1471-9053},
	doi = {10.1093/pcp/pcaa061},
	author = {Somasundaram, Suji and V{\'e}ry, Anne-Ali{\'e}nor and Vinekar, Rithvik S and Ishikawa, Tetsuya and Kumari, Kumkum and Pulipati, Shalini and Kumaresan, Kavitha and Corratg{\'e}-Faillie, Claire and Sowdhamini, R and Parida, Ajay and Shabala, Lana and Shabala, Sergey and Venkataraman, Gayatri}
}
