An extracellular matrix protein in plants: characterization of a genomic clone for carrot extensin.

Extensins are hydroxyproline-rich glycoproteins found in many plant cell walls as a major protein component. The peptide Ser-Hyp-Hyp-Hyp-Hyp is abundant in the extensins. Using extensin cDNA clones as probes, we isolated six different clones from carrot genomic libraries. One of the genomic clones, pDC5A1, was characterized and found to contain an open reading frame encoding extensin and a single intron in the 3'-non-coding region. The derived amino acid sequence contains a signal peptide sequence and 25 Ser-Pro-Pro-Pro-Pro repetitive sequences. Two extensin transcripts were found corresponding to pDC5A1 with different 5' start sites. These transcripts increased in abundance after wounding. This is consistent with the reported extensin accumulation in the cell wall upon wounding.