The chloroplast small heat shock proteins (Cp-sHSP) protect photosystem II and thylakoid membranes during heat and other types of stresses. The amount of Cp-sHSPs produced is correlated with plant thermotolerance. Cp-sHSPs of Chenopodium album have already been shown to be heat-regulated and have a novel promoter architecture containing some conserved regulatory motifs Shakeel et al. (Plant Physiol Biochem 49:898-908, 2011). To determine if similar or different Cp-sHSP isoforms protect plants against heat and metal stress, we isolated and characterized a novel Cp-sHSP isoform, CaHSP26. 13p (GI # JX073659) from a Pakistani C. album ecotype and determined its expression under heat and metal stress by measuring transcript and protein levels. Presence of the same CaHSP26. 13p transcript in heat- and metal-treated plants provided evidence of heat- and metal-regulated expression. Gene expression analysis indicated that Cp-sHSP transcript levels were maximum at 37 °C for 4 h (heat stress) and 20 mM cadmium (metal stress). Immunoblot analysis revealed that (1) maximum expression of precursor and processed protein was observed at 37 °C in the case of heat stress, (2) while only precursor protein of ~26 kDa was produced in the case of metal stress. The highest expression occurred when plants were treated with 15 mM cadmium. We speculate that post-translational regulation accounted for the lack of correlation between transcript and protein levels. This study demonstrates that differential regulation of the same C. album Cp-sHSP family member enables it to play a dual role in protecting the plant from heat and metal stress.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Plant Science