Transcriptome and Cell Physiological Analyses in Different Rice Cultivars Provide New Insights Into Adaptive and Salinity Stress Responses

Abstract

Salinity tolerance has been extensively investigated in recent years due to its agricultural importance. Several features, such as the regulation of ionic transporters and metabolic adjustments, have been identified as salt tolerance hallmarks. Nevertheless, due to the complexity of the trait, the results achieved to date have met with limited success in improving the salt tolerance of rice plants when tested in the field, thus suggesting that a better understanding of the tolerance mechanisms is still required. In this work, differences between two varieties of rice with contrasting salt sensitivities were revealed by the imaging of photosynthetic parameters, ion content analysis and a transcriptomic approach. The transcriptomic analysis conducted on tolerant plants supported the setting up of an adaptive program consisting of sodium distribution preferentially limited to the roots and older leaves, and in the activation of regulatory mechanisms of photosynthesis in the new leaves. As a result, plants resumed grow even under prolonged saline stress. In contrast, in the sensitive variety, RNA-seq analysis revealed a misleading response, ending in senescence and cell death. The physiological response at the cellular level was investigated by measuring the intracellular profile of H2O2 in the roots, using a fluorescent probe. In the roots of tolerant plants, a quick response was observed with an increase in H2O2 production within 5 min after salt treatment. The expression analysis of some of the genes involved in perception, signal transduction and salt stress response confirmed their early induction in the roots of tolerant plants compared to sensitive ones. By inhibiting the synthesis of apoplastic H2O2, a reduction in the expression of these genes was detected. Our results indicate that quick H2O2 signaling in the roots is part of a coordinated response that leads to adaptation instead of senescence in salt-treated rice plants.

Analysis and Modeling of Processes Involved with Salt Tolerance and Rice

“…This is in agreement with Formentin et al (2018), who reported that the preactivation of leaf tolerance mechanisms before the onset of ionic stress confers to this cultivar a certain level of salt tolerance. This is in agreement with Formentin et al (2018), who reported that the preactivation of leaf tolerance mechanisms before the onset of ionic stress confers to this cultivar a certain level of salt tolerance.…”

“…Baldo did not control Na + uptake as effectively as Vialone Nano, whereas it was more able to tolerate Na + concentration in tissues, in turn supporting crop growth even under salt stress conditions. This is in agreement with Formentin et al (2018), who reported that the preactivation of leaf tolerance mechanisms before the onset of ionic stress confers to this cultivar a certain level of salt tolerance. However, the analysis of panicle biomass data suggested that Baldo could be more susceptible to salt-induced sterility for grain yield, although further experiments are needed to confirm this finding.…”

“…In the first experiment, two Italian cultivars, Baldo and Vialone Nano (sensitive and highly sensitive to salt stress, respectively; Bertazzini et al, 2018;Formentin et al, 2018), were grown. Five NaCl treatments (0, 10, 25, 35, and 50 mM) were applied starting from 3 wk after sowing until maturity.…”

Effect of Different Water Salinity Levels on the Germination of Imazamox-Resistant and Sensitive Weedy Rice and Cultivated Rice

“…Baldo was chosen, not only as being not resistant to imazamox, but also because it was one of the most cultivated rice varieties in Italy, with an economic importance also for the export market [35]. This variety has demonstrated a certain degree of salt tolerance at the seedling stage [36], but only poor information is available on the germination response to salt. The variety CL80 was included as representative of imazamox-resistant varieties.…”

Identification and Validation a Major QTL from “Sea Rice 86” Seedlings Conferred Salt Tolerance

“…Rice is considered as most susceptible to salt stress in the seedling, reproductive, and 2-3 leaf stages [6]. Previous investigations clarified that salinity influences rice growth in three phases: osmotic stress, ionic toxicity, and oxidative stress; and salt tolerance is a comprehensive quantitative trait involving both genetic characteristics and physiological responses [7][8][9].…”