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Salt tolerance in indica rice cell cultures depends on a fine tuning of ROS signalling and homeostasis.

ABSTRACT: Among cereal crops, salinity tolerance is rare and complex. Multiple genes control numerous pathways, which constitute plant's response to salinity. Cell cultures act as model system and are useful to investigate the salinity response which can possibly mimic a plant's response to stress. In the present study two indica rice varieties, KS-282 and Super Basmati which exhibited contrasting sodium chloride (NaCl) stress response were used to establish cell cultures. The cell cultures showed a contrasting response to salt stress at 100 mM NaCl. High level of intracellular hydrogen peroxide (H2O2) and nitric oxide (NO) were observed in sensitive cell culture for prolonged period as compared to the tolerant cells in which an extracellular H2O2 burst along with controlled intracellular H2O2 and NO signal was seen. To evaluate the role of NO in inducing cell death under salt stress, cell death percentage (CDP) was measured after 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) pre-treatment. CDP was reduced significantly in both tolerant and sensitive cell cultures emphasizing NO's possible role in programmed cell death. Expression analysis of apoplastic NADPH oxidase, i.e. OsRbohA and recently characterised OSCA family members i.e. OsOSCA 1.2 and OsOSCA 3.1 was done. Intracellular H2O2/NO levels displayed an interplay between Ca2+ influx and ROS/RNS signal. Detoxifying enzyme (i.e. ascorbate peroxidase and catalase) activity was considerably higher in tolerant KS-282 while the activity of superoxide dismutase was significantly prominent in the sensitive cells triggering greater oxidative damage owing to the prolonged presence of intracellular H2O2. Salt stress and ROS responsive TFs i.e. OsSERF1 and OsDREB2A were expressed exclusively in the tolerant cells. Similarly, the expression of genes involved in maintaining high [K+]/[Na+] ratio was considerably higher and earlier in the tolerant variety. Overall, we suggest that a control over ROS production, and an increase in the expression of genes important for potassium homeostasis play a dynamic role in salinity tolerance in rice cell cultures.

SUBMITTER: Ijaz B

PROVIDER: S-EPMC6490951 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: The bZIP class Abscisic acid Responsive Element (ABRE)-binding factor, OSBZ8 (38.5 kD) has been considered to regulate ABA-mediated transcription in the suspension cultured cells of japonica rice. Still, nothing is known about the expression of OSBZ8 at protein level in vegetative tissue of salt sensitive and salt tolerant rice plants. In our previous study, Electrophoretic Mobility Shift Assay (EMSA) of [32P]ABRE-DNA and nuclear extracts prepared from the lamina of Pokkali rice plants has detected the presence of an ABRE-binding factor. Northern analysis has also detected salinity stress induced accumulation of transcripts for bZIP class of factor. Therefore, OSBZ8 was considered to play an important role in the regulation of transcription in the vegetative tissue of rice. The aim of this study is to find out whether OSBZ8 has any role in regulating the NaCl-stress induced gene expression in vegetative tissue and whether the expression of OSBZ8 factor directly correlates with the stress tolerance of different varieties of indica type rice. RESULTS: Northern analysis of total RNA from roots and lamina of salt-sensitive M-I-48 and salt-tolerant Nonabokra, when probed with the N-terminal unique region of OSBZ8 (OSBZ8p, without the highly conserved basic region), a transcript of 1.3 kb hybridized and its level was much higher in tolerant cultivar. EMSA with Em1a, the strongest ABA Responsive Element till reported from the upstream of EmBP1, and the nuclear extracts from laminar tissue of untreated and salt-treated seedlings of three salt sensitive, one moderately sensitive and two salt tolerant indica rice cultivars showed specific binding of nuclear factor to ABRE element. Intensity of binding was low and inducible in salt sensitive rice cultivars while high and constitutive in salt tolerant cultivars. EMSA with 300 bp 5'upstream region of Rab16A gene, a well known salt stress and ABA-inducible gene of rice, showed formation of two complexes, again very weak in salt sensitive and strong in salt tolerant rice cultivar. CONCLUSION: The bZIP factor OSBZ8 was found to be present in the ABRE-DNA: protein complex as shown by the supershift of the complex by the purified antiserum raised against OSBZ8p. Treatment of the seedlings with NaCl was found to enhance the complex formation, suggesting the regulation of OSBZ8 gene at both transcriptional and post-translational steps. Comparative EMSA with different varieties of rice suggests a positive correlation with the expression pattern of OSBZ8 and salt tolerance in rice cultivars.

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Salt tolerance in indica rice cell cultures depends on a fine tuning of ROS signalling and homeostasis.

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