Homologues of a vacuolar processing enzyme that are expressed in different organs in Arabidopsis thaliana

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Abstract
Vacuolar processing enzymes (VPEs) are responsible for the maturation of seed proteins. These processing enzymes belong to a novel group of cysteine proteinases with molecular masses of 37 to 39 kDa. We isolated two genes of VPEs from a genomic library of Arabidopsis. The gene products were designated α-VPE and β-VPE, and they were 56% identical in terms of amino acid sequence. The amino acid sequences of α-VPE and β-VPE were also 55% and 67% identical to that of castor bean VPE, respectively. The gene for α-VPE had 7 introns, while that of β-VPE had 8 introns. Northern blot analysis revealed that α-VPE is expressed in rosette leaves, cauline leaves and stems of Arabidopsis, while β-VPE is predominantly expressed in the flowers and buds. Neither α-VPE nor β-VPE is expressed in the siliques. This result strongly suggests that the isolated genes encode isozymes of VPE that are specific to vegetative organs.