Format: ORAL

Ping Yun1,2, Lana Shabala1,3, Meixue Zhou1, Zhonghua Chen4, Gayatri Venkataraman5, Sergey Shabala2,3

1 Tasmanian Institute of Agriculture, University of Tasmania, Hobart, Australia 2 School of Biological Science, University of Western Australia, Perth, Australia 3 International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, China 4 School of Science, Western Sydney University, Penrith, Australia 5 Plant Molecular Biology laboratory, M. S. Swaminathan Research Foundation, Chennai, India

Oryza coarctata is the only halophytic relative in the genus Oryza that is tolerant to high salinity levels. In this work, we investigated key traits that confer this exceptional salt tolerance in O. coarctata, comparing it with responses of cultivated Oryza sativa species. We show that O. coarctata is utilizing Na+ for stomata operation and, as result, is capable to maintain unaltered stomatal related traits (size, density, and opening speed). These plants had also enhanced RuBisCO carboxylation and RuBP regeneration in the Calvin cycle. Taken together, these features allowed O. coarctata maintain relative steady CO2 assimilation under salt conditions. Upon exposure to salinity, wild rice also quickly increased xylem Na+ loading for osmotic adjustment but maintained non-toxic level of stable shoot Na+ concentration by increased activity of HKT1;5 (essential for xylem Na+ unloading) and a Na+/H+ exchanger NHX (for sequestering Na+ and K+ into root vacuoles). In contrast, cultivated rice prevented Na+ uptake and transport to the shoot at the beginning of salt treatment but failed to maintain it in a long-term. We also show that wild rice limits passive Na+ entry into root cells while cultivated rice relies heavily on SOS1-mediating Na+ exclusion, with major penalties imposed by the existence of the “futile cycle” at the plasma membrane. Other traits that contributed to superior salinity tolerance in O. coarctata included more efficient ROS signalling; desensitization of ROS-inducible cation channels and more superior K+ retention in the cytosol; more effective control of cytosolic Ca2+ homeostasis by Ca2+-ATPase and CAX-mediated Ca2+ efflux systems; and ability to prevent salt-induced downregulation of RBOH expression that may affect operation of the “ROS-Ca2+ hub” and signalling cascades under salinity.