Several novel Arabidopsis thaliana proteins containing a RING-H2 zinc finger motif were predicted after database searches. Alignment of 29 RING-H2 finger sequences shows that the motif is strikingly conserved in otherwise unrelated proteins. Only short, non-conserved polar/charged sequences distinguish these domains. The RING-H2 domain is most often present in multi-domain structures, a number of which are likely to contain a membrane-spanning region or an additional zinc finger. However, there are several small (126-200 residues) proteins consisting of an N-terminal domain, rich in aliphatic residues, and a C-terminal RING-H2 domain. Reverse-transcription PCR suggests that the RING-H2 genes are widely expressed at low levels.

Suppression subtractive hybridization (SSH) was applied in the search of the genes induced during the interaction between Phytophthora infestans and horizontal resistance potato (R-gene-free). A subtractive library of potato, which highly enriches for resistance-related genes to P. infestans, was constructed. The potato leaves after inoculating 48 h with mixture of P. infestans races were used as "tester" and uninoculated leaves as "control" in the experiments. Total 150 of 840 randomly chosen cDNA clones were identified with the reveres Northern dot-blot screening method. The sequencing results of 26 clones indicated that several fragments were previously shown to be activated during resistance responses. Seven differentially expressed fragments had significant homologous with EST of potato leaves inoculated with P. infestans. The sequences of nucleotide or amino acids of partial cDNA fragments shared identity with tomato, tobacco and Arabidopsis while four cDNA fragments that had no significant homology with EST in GenBank were expected to be new genes involved in the disease response.

Really interesting new gene (RING) finger proteins function as ubiquitin ligase and play key roles in biotic and abiotic stresses. A new RING-H2 finger protein gene, StRFP1, was cloned from Phytophthora infestans-inoculated leaves of potato (Solanum tuberosum) clone 386209.10, which is free of R1-R11 genes. The deduced amino acid sequence was characterized by an N-terminal transmembrane domain, a GLD region and a RING-H2 finger signature. StRFP1 is homologous to the tobacco NtACRE132 protein and belongs to the ATL family. The DNA gel blot analysis and mapping revealed that StRFP1, an intron-free gene, had one to two copies in the potato genome and was located on chromosome 3. RT-PCR assays showed that StRFP1 was constitutively expressed in potato plants and significantly induced in detached potato leaves by P. infestans and plant defense-related signal molecules, abscisic acid, salicylic acid and methyl jasmonate. Transient expression studies revealed that StRFP1 fused with GFP localized to the plasma membrane or out of that in onion epidermal cells. The function of StRFP1 in potato resistance against late blight was further investigated by constructing overexpression and RNA interference (RNAi) vectors, which were introduced into potato cv. E-potato 3, respectively. By challenging the detached leaves with mixture races of P. infestans, all of the StRFP1-overexpressing plants displayed slower disease development than non-transformed controls in terms of the lesion growth rate (LGR). In contrast, StRFP1-silencing plants through RNAi were more susceptible to pathogen infection. The present results demonstrate that StRFP1 contributes to broad-spectrum resistance against P. infestans in potato.