Newly Identified Wild Rice Accessions Conferring High Salt Tolerance Might Use a Tissue Tolerance Mechanism in Leaf

Abstract

Cultivated rice (Oryza sativa L.) is very sensitive to salt stress. So far a few rice landraces have been identified as a source of salt tolerance and utilized in rice improvement. These tolerant lines primarily use Na+ exclusion mechanism in root which removes Na+ from the xylem stream by membrane Na+ and K+ transporters, and resulted in low Na+ accumulation in shoot. Identification of a new donor source conferring high salt tolerance is imperative. Wild relatives of rice having wide genetic diversity are regarded as a potential source for crop improvement. However, they have been less exploited against salt stress. Here, we simultaneously evaluated all 22 wild Oryza species along with the cultivated tolerant lines including Pokkali, Nona Bokra, and FL478, and sensitive check varieties under high salinity (240 mM NaCl). Based on the visual salt injury score, three species (O. alta, O. latifolia, and O. coarctata) and four species (O. rhizomatis, O. eichingeri, O. minuta, and O. grandiglumis) showed higher and similar level of tolerance compared to the tolerant checks, respectively. All three CCDD genome species exhibited salt tolerance, suggesting that the CCDD genome might possess the common genetic factors for salt tolerance. Physiological and biochemical experiments were conducted using the newly isolated tolerant species together with checks under 180 mM NaCl. Interestingly, all wild species showed high Na+ concentration in shoot and low concentration in root unlike the tolerant checks. In addition, the wild-tolerant accessions showed a tendency of a high tissue tolerance in leaf, low malondialdehyde level in shoot, and high retention of chlorophyll in the young leaves. These results suggest that the wild species employ tissue tolerance mechanism to manage salt stress. Gene expression analyses of the key salt tolerance-related genes suggested that high Na+ in leaf of wild species might be affected by OsHKT1;4-mediated Na+ exclusion in leaf and the following Na+ sequestration in leaf might be occurring independent of tonoplast-localized OsNHX1. The newly isolated wild rice accessions will be valuable materials for both rice improvement to salinity stress and the study of salt tolerance mechanism in plants.

Anthropogenic Changes in a Mediterranean Coastal Wetland during the Last Century—The Case of Gialova Lagoon, Messinia, Greece

“…Even though Typha species are invasive, dominating over native aquatic species under moderate salinity, they can germinate only after being returned to non-saline conditions [39], and the most salt-tolerant species (Typha domingensis) can only tolerate salinities up to 15 ppt [40,41]. In addition, rice, which according to the KIs and historical maps, was also cultivated in the area prior to 1960, is a salt-sensitive crop that becomes unproductive when soil salinity reaches 7 ppt [42].…”

Tissue Tolerance Coupled With Ionic Discrimination Can Potentially Minimize the Energy Cost of Salinity Tolerance in Rice

“…The chlorophyll content, ChlF imaging, and tissue ion contents (Na + and K + ) were estimated as described above, on a daily basis, from both freshwater-and saline water-dipped sample. From the collected data, daily chlorophyll degradation rate and tissue tolerance (LC 50 score represents a sodium concentration where half (50%) of the chlorophyll pigments were destroyed) was calculated for each genotype (Prusty et al, 2018).…”

“…This can also be achieved by maintaining the cellular ionic homeostasis by effective K + retention (Munns and Tester, 2008). Previous studies reported genetic variations in rice for salt-tolerance strategies (Roy et al, 2014;Prusty et al, 2018;Chakraborty et al, 2019). The mechanism of ion exclusion is strongly associated with the expression of SOS pathway genes, where salt stress induces calcium signal by activating SOS2/SOS3 complex, which further activates SOS1, a plasma membrane Na + /H + antiporter (Martinez-Atienza et al, 2007;Munns and Tester, 2008).…”

Salt‐Treated Roots of Oryza australiensis Seedlings are Enriched with Proteins Involved in Energetics and Transport

“…Indeed, several breeding programmes have used O. sativa cultivars, such as Pokkali and Nona Bokra, as salt‐tolerant parent donors, incorporating Saltol and other salt tolerance genes . However, the allelic variation required to breed stress‐tolerant crops must now be expanded by introgressing genes from wild relatives because of the relatively small proportion of the total genetic diversity in the genus Oryza found in O. sativa . Salinity tolerance of other key crop species, such as durum wheat ( Triticum durum ) and tomato ( Solanum lycopersicum ), has been improved using natural allelic variation.…”

“…Endemic Australian rice species have been identified as a source of tolerance to abiotic and biotic stress in cultivated rice . Tissue tolerance to Na + in seven pantropical wild rice species was reported recently, implying the presence of key tolerance genes in the Oryza CC and DD genomes . Membrane transporters are a vital part of the control of influx, efflux, and partitioning of Na + and Cl − .…”