Cloning and characterization of an 18 kiloDalton protein in the roots of the perennial weed Taraxacum officinale Weber (Dandelion) which has allergen- and pathogenesis-related protein properties

The root of the persistent weed, dandelion (Taraxacum officinale Weber), co ntains a predominant 18 kDa protein which undergoes small seasonal fluctuat ions in amount, increasing in the late autumn months, and declining in the spring. This protein has been purified and found to consist of two major is oforms of pI 5.56 and pI 5.49. A full-length cDNA has been obtained, coding for the pI 5.56 isoform, and the 156-amino-acid sequence deduced. The prot ein shows homologies in amino acid composition to several allergen and intr acellular pathogenesis-related proteins. The deduced protein does not conta in a signal peptide nor any known organelle-targeting sequences, and thus i s likely to be cytosolic. Expression of the 18 kDa protein gene is exclusiv e to the roots and stem tissues; transcripts accumulate during the late aut umn months, and decline in the early spring. Changes in the amount of prote in in the root are much less. The mRNA for the 18 kDa protein is not presen t in the dry seed, but appears in the roots within 16-18 h from the start o f imbibition, and is expressed constitutively thereafter. Although it is th e predominant protein in dandelion roots, its properties are different from those commonly associated with vegetative storage proteins.