Heat stress inducible cytoplasmic isoform of ClpB1 from Z. nummularia exhibits enhanced thermotolerance in transgenic tobacco.

Previously, we isolated CDS of Ziziphus nummularia isoform ZnJClpB1-C from heat stress-tolerant genotype Jaisalmer. To further functionally validate ZnJClpB1-C assumed function in tobacco and to generate novel germplasm for heat stress tolerance, this gene was transformed in the Nicotiana tabacum. ClpB proteins are the major key player required for basal and induced heat stress tolerance in plant cells under heat stress. In Ziziphus nummularia ClpB1-C transcript from genotype Jaisalmer was highly upregulated under heat stress conditions, as reported earlier. Nine transgenic lines (T₁) from three transgenic tobacco events with single-copy integration (T₀ stage) were taken for heat stress analysis at seedling stage. Mature tobacco transgenic plants did not show any deformity as compared to wild plants when grown under normal conditions. Overexpression of ZnJClpB1-C in tobacco significantly increased the tolerance to heat stress. Under heat stress conditions (42 °C), T₁ transgenic tobacco seedlings showed higher photosynthetic rate, relative water content, membrane stability index and lower levels of MDA, compared to the wild type untransformed plants. The qRT-PCR analysis revealed different level of transgene expression (1.08 to 3.89 folds) in 9 T₁ transgenic lines. In vitro roles of ZnJClpB1-C regulating thermotolerance is not reported so far. These results demonstrated the positive roles of ZnJClpB1-C in enhancing thermotolerance and its use as a genomic resource in the near future for developing heat stress-tolerant germplasm.