Abstract:

A cDNA clone encoding HsfA1d was isolated from a cDNA library prepared under heat shock stress in Populus simonii by the RT-PCR method. The cDNA of PsHsfA1d is 2 036 bp in length with an open reading frame (ORF, 1 449 bp in length) which is capable of encoding a protein of 482 amino acids. The deduced protein sequence of the PsHsfA1d shares 86.3％, and 87.4％ identity with functional domain of HSF DBD of Arabidopsis thaliana AtHsfA1d, and Oryza sativa OsHsfA 1 , respectively. Tissue differential expression with realtime-PCR indicated that PsHsfA1d was expressed predominantly in the leaves and roots. We analyzed the expression patterns of PsHsfA1d under abiotic stress conditions and phytohormone treatment, and the result revealed that expression of PsHsfA1d was induced not only by heat-shock, drought and high-salt stress, but also up regulated by GA₃, and ABA, and glucose and sucrose signals. The genomic sequences of PsHsfA1d in 36 individuals were aligned, compared and analyzed using the software MEGA4.0 and DnaSP4.50.7. A total of 207 single nucleotide polymorphisms (SNPs) were detected and the frequency and diversity of SNPs were 1/16 bp and 0.007 72, respectively. In total, 69 SNPs were detected in the coding regions of PsHsfA1d, of which 37, 31 and 1 were silent, missense, and nonsense mutations, respectively; the nonsynonymous nucleotide substitutions (π_nonsyn) was markedly lower than π_syn, with the π_nonsyn/π_syn ratio 0.132＜1, suggesting that diversity at the synonymous sites of exon regions would have resulted from strong purifying selection.

Key words: Populus simonii, HsfA1d gene, heat shock stress, inducible expression, single nucleotide polymorphisms