Background
Drought stress is one of the major abiotic stresses that adversely affect rice production. Four rice genotypes, Giza177, IR64 (as sensitive genotypes) and Vandana, Orabi3 (as tolerant genotypes) were used to screen and characterize the soil microbes associated with each genotype under drought stress.
Results
The soil microbes associated with the tolerant genotypes showed high drought tolerance and high levels of enzyme activity. The most drought-tolerant isolates were inoculated with the sensitive genotype Giza177 under drought conditions. Some morphological, biochemical and molecular responses of inoculated plants were estimated. Inoculated plants showed regulation of some growth and stress-related genes (COX1, AP2-EREBP, GRAM, NRAMP6, NAM, GST, DHN and three genes of expansin (EXP1, EXP2 and EXP3) under drought conditions. Expression profiling of these genes were highly induced in plants inoculated with 4E11 and were correlated with improved growth status under drought stress.
Conclusion
Based on this, drought-tolerant plant growth-promoting rhizobacteria (PGPRs) were associated with the drought-tolerant genotype (Orabi 3). They were related to the significant increase in soil enzymes activities (dehydrogenase, nitrogenase, urease and alkaline phosphatase) in the rhizosphere of tolerant genotype. Inoculation the drought-sensitive genotype (Giza 177) with the most drought-tolerant isolates improved the tolerance status of the sensitive rice genotype and induced the expression of some growth and stress-responsive genes. AP2-EREBP, NRAMP6, DHN and all expansin genes (EXP1, EXP2 and EXP3) were the highly induced genes in inoculated plants with 4E11 strain and the consortium of three selected strains under drought condition.
Graphic abstract
Plant dehydrin proteins (DHNs) are known to be important for environmental stress tolerance and are involved in various developmental processes. Two full-length cDNAs JcDHN-1 and JcDHN-2 encoding two dehydrins from Jatropha curcas seeds were identified and characterized. JcDHN-1 is 764 bp long and contains an open reading frame of 528 bp. The deduced JcDHN-1 protein has 175 a.a. residues that form a 19.3-kDa polypeptide with a predicted isoelectric point (pI) of 6.41. JcDHN-2 is 855 bp long and contains an open reading frame of 441 bp. The deduced JcDHN-2 protein has 156 a.a. residues that form a 17.1-kDa polypeptide with a predicted pI of 7.09. JcDHN-1 is classified as type Y₃SK₂ and JcDHN-2 is classified as type Y₂SK₂ according to the YSK shorthand for structural classification of dehydrins. Homology analysis indicates that both JcDHN-1 and JcDHN-2 share identity with DHNs of other plants. Analysis of the conserved domain revealed that JcDHN-2 has glycoside hydrolase GH20 super-family activity. Quantitative real time PCR analysis for JcDHN-1 and JcDHN-2 expression during seed development showed increasing gene expression of both their transcript levels along with the natural dehydration process during seed development. A sharp increase in JcDHN-2 transcript level occurred in response to water content dropping from 42% in mature seeds to 12% in dry seeds. These results indicate that both JcDHNs have the potential to play a role in cell protection during dehydration occurring naturally during jatropha orthodox seed development.
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