SEQUENCE AND RT-PCR EXPRESSION ANALYSIS OF 2 PEROXIDASES FROM ARABIDOPSIS-THALIANA BELONGING TO A NOVEL EVOLUTIONARY BRANCH OF PLANT PEROXIDASES

cDNA clones encoding two new Arabidopsis thaliana peroxidases, ATP la and ATP 2a, have been identified by searching the Arabidopsis database of expressed sequence tags (dbEST). They represent a novel branch of hitherto uncharacterized plant peroxidases which is only 35% identical in amino acid sequence to the well characterized group of basic plant peroxidases represented by the horseradish (Armoracia rusticana) isop eroxidases HRP C, HRP E5 and the similar Arabidopsis isoperoxidases AT P Ca, ATP Cb, and ATP Ea. However ATP 1a is 87% identical in amino aci d sequence to a peroxidase encoded by an mRNA isolated from cotton (Go ssypium hirsutum). As cotton and Arabidopsis belong to rather diverse families (Malvaceae and Crucifereae, respectively), in contrast with A rabidopsis and horseradish (both Crucifereae), the high degree of sequ ence identity indicates that this novel type of peroxidase, albeit of unknown function, is likely to be widespread in plant species. The atp 1 and atp 2 types of cDNA sequences were the most redundant among the 28 different isoperoxidases identified among about 200 peroxidase enc oding ESTs. Interestingly, 8 out of totally 38 EST sequences coding fo r ATP 1 showed three identical nucleotide substitutions. This variant form is designated ATP Ib. Similarly, six out of totally 16 EST sequen ces coding for ATP 2 showed a number of deletions and nucleotide chang es. This variant form is desigated ATP 2b.