An enzyme similar to animal type II photolyases mediates photoreactivation in Arabidopsis

The important issue of photoreactivation DNA repair in plants has become even more interesting in recent years because a family of genes that are highly homologous to photoreactivating DNA repair enzymes but that function as blue light photoreceptors has been isolated. Here, we report the isolation of a novel photolyase-like sequence from Arabidopsis designated PHR1 (for photoreactivating enzyme). It shares little sequence similarity with either type I photolyases or the cryptochrome family of blue light photoreceptors. Instead, the PHR1 gene encodes an amino acid sequence with significant homology to the recently characterized type II photolyases identified in a number of prokaryotic and animal systems. PHR1 is a single-copy gene and is not expressed in dark-grown etiolated seedlings: the message is light inducible, which is similar to the expression profile for photoreactivation activity in plants. The PHR1 protein complements a photolyase-deficient mutant of Escherichia coli and thus confers photoreactivation activity. In addition, an Arabidopsis mutant that is entirely lacking in photolyase activity has been found to contain a lesion within this Arabidopsis type II photolyase sequence. We conclude that PHR1 represents a genuine plant photolyase gene and that the plant genes with homology to type I photolyases (the cryptochrome family of blue light photoreceptors) do not contribute to photoreactivation repair, at least in the case of Arabidopsis.