Identification of genes induced during Medicago sativa nodule development by using the cDNA-AFLP technique

Cloning and characterization of a heat shock protein 70 gene, MsHSP70-1, in Medicago sativa

Some members of the heat shock protein 70 (HSP70) family have important functions in organism development. Here, we identified an alfalfa (Medicago sativa L. cv. Algonquin) HSP70 gene, MsHSP70-1, using cDNA array and reverse transcription-polymerase chain reaction. This gene contains a 1947 bp open reading frame encoding a protein of 649 amino acids. This protein contains all conserved domains, motifs, and characteristic sequences of plant HSP70s. The expression of MsHSP70-1 is enhanced in nodule compared with root, stem, leaf, and flower, and throughout the process of nodule development. Northern hybridization analysis indicated that the expression of MsHSP70-1 in nodule requires the active bacA gene of rhizobia. These results suggested that MsHSP70-1 might play an important role in alfalfa nodule development.

Structure and alternative splicing of a heat shock transcription factor gene, MsHSF1, in Medicago sativa

Plant heat shock transcription factors (HSF) are highly complex. In this study, we identified an alfalfa HSF gene MsHSF1 that is composed of four exons and three introns in the encoding region. The intron1-exon2-intron2-exon3-intron3 as an intervening sequence was inserted at the conserved position that separates the coding region for the DNA-binding domain by single intron in other known plant HSF genes. Alternative splicing of MsHSF1 has generated five transcript isoforms. Spliced transcript MsHSF1b consisted of exon1 and exon4, encodes a class A1 HSF protein that can specifically bind to the heat shock elements in vitro. Other four spliced transcripts (MsHSF1a-1 to 4) consist of exon1, part of the intervening sequence and exon4. These transcripts carry the premature termination codon and are low-abundant. Apparently these transcripts are the targets of nonsense-mediated mRNA decay (NMD). These results provide new insight into roles in the expression regulation of plant HSF genes.