A collection of cDNAs was isolated from a λgt11 potato ( Solanum tuberosum L.) tuber library by using a soybean lipoxygenase (LOX; linoleate:oxygen oxidoreductase, EC 1.13.11.12) sequence as a hybridization probe. These cDNA clones were classified by restriction patterns and sizes and two clones, plox 1 and plox 2, were selected for sequencing and further analysis. These clones were found to be virtually identical and contain full‐length cDNAs having a high degree of homology with other cloned LOX genes. plox 1 contains a 2 806‐bp insert, with an open reading frame that encodes a protein of 861 amino acids (96.9 kDa), consistent with molecular mass estimates of the principal tuber LOX deduced from SDS‐PAGE. The deduced sequence contains iron‐binding domains that are conserved among LOXs. Restriction analysis of potato genomic DNA confirmed that potato LOX is comprised of a gene family with at least three members. The plox 1 sequence hybridized to a transcript of 2.8 kb in gel blot analyses of total RNA extracted from potato tuber. Treatment of potato disks and leaves with methyl jasmonate or jasmonic acid increased LOX enzyme activity, as well as abundance of LOX mRNA, consistent with jasmonate's reported effect on LOX expression in plants. The fungal elicitor arachidonic acid (AA) strongly induced LOX enzyme activity in leaves and induced LOX mRNA transcripts in potato leaves and tuber disks. Infection of potato leaves with Phytophthora infestans induced LOX activity as well as LOX mRNA accumulation in both incompatible and compatible interaction types. LOX expression was compared with that of a wound‐inducible proteinase inhibitor (PINII) and a pathogenesis‐related protein (P4). Jasmonates induced PINII but not P4 transcript accumulation in potato leaves. In contrast, AA induced P4 but not PINII transcript accumulation in potato leaves. Infection with P. infestans resulted in a gene expression pattern similar to that observed with AA.
Abstract Ultraviolet radiation induces DNA damage products, largely in the form of pyrimidine dimers, that are both toxic and mutagenic. In most organisms, including Arabidopsis, these lesions are repaired both through a dimer-specific photoreactivation mechanism and through a less efficient light-independent mechanism. Several mutants defective in this “dark repair” pathway have been previously described. The mechanism of this repair has not been elucidated, but is thought to be homologous to the nucleotide excision repair mechanisms found in other eukaryotes. Here we report the complementation of the Arabidopsisuvh1 dark repair mutant with the Arabidopsis homolog of the yeast nucleotide excision repair gene RAD1, which encodes one of the subunits of the 5′-repair endonuclease. Theuvh1-2 mutant allele carries a glycine→aspartate amino acid change that has been previously identified to produce a null allele of RAD1 in yeast. Although Arabidopsis homologs of genes involved in nucleotide excision repair are readily identified by searching the genomic database, it has not been established that these homologs are actually required for dark repair in plants. The complementation of the Arabidopsisuvh1 mutation with the Arabidopsis RAD1homolog clearly demonstrates that the mechanism of nucleotide excision repair is conserved among the plant, animal, and fungal kingdoms.
