Cloning and expression of a small heat shock protein gene CaHSP24 from pepper under abiotic stress
The sequence of a small heat shock protein (sHSP) gene CaHSP24 was obtained by homology-based candidate gene method and rapid amplification of cDNA ends (RACE). The cDNA sequence of this gene is 920 bp in size (GenBank: HM132040) and contains an open reading frame (ORF) of 636 bp, which was predicted to encode a protein with 211 amino acid residues. The phylogenetic tree showed that CaHSP24 was quite similar to mitochondrial sHSPs from other plants but was distantly related to sHSPs of pepper cytoplasm and chloroplast. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) showed that CaHSP24 was hardly detectable at 32°C, but accumulated markedly at 40°C. The gene was expressed 0.5 h after exposure to heat stress and the expression reached a peak in 1.5 h; the expression level in heat-resistant cultivar B35 was higher than that in heat-sensitive cultivar B6. The gene was also expressed weakly under salinity, heavy metal, low temperature and oxidative stresses; the expression levels under these conditions were remarkably lower than those under heat stress. Cell viability experiments showed that the heterologous expression of CaHSP24 could enhance the viability of Escherichia coli under heat stress. To sum up, CaHSP24 may play an important role for response to heat stress condition.
Key words: Pepper, CaHSP24, heat stress, gene expression.