Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating potato disease in the world. Control of late blight in the United States and other developed countries relies extensively on fungicide application. We previously demonstrated that the wild diploid potato species Solanum bulbocastanum is highly resistant to all known races of P. infestans. Potato germplasm derived from S. bulbocastanum has shown durable and effective resistance in the field. Here we report the cloning of the major resistance gene RB in S. bulbocastanum by using a map-based approach in combination with a long-range (LR)-PCR strategy. A cluster of four resistance genes of the CC-NBS-LRR (coiled coil-nucleotide binding site-Leu-rich repeat) class was found within the genetically mapped RB region. Transgenic plants containing a LR-PCR product of one of these four genes displayed broad spectrum late blight resistance. The cloned RB gene provides a new resource for developing late blight-resistant potato varieties. Our results also demonstrate that LR-PCR is a valuable approach to isolate genes that cannot be maintained in the bacterial artificial chromosome system.

Studies with mutants in four members of the five-membered Arabidopsis phytochrome (phy) family (phyA, phyB, phyD, and phyE) have revealed differential photosensory and/or physiological functions among them, but identification of a phyC mutant has proven elusive. We now report the isolation of multiple phyC mutant alleles using reverse-genetics strategies. Molecular analysis shows that these mutants have undetectable levels of phyC protein, suggesting that they are null for the photoreceptor. phyC mutant seedlings were indistinguishable from wild-type seedlings under constant far-red light (FRc), and phyC deficiency had no effect in the phyA mutant background under FRc, suggesting that phyC does not participate in the control of seedling deetiolation under FRc. However, when grown under constant red light (Rc), phyC seedlings exhibited a partial loss of sensitivity, observable as longer hypocotyls and smaller cotyledons than those seen in the wild type. Although less severe, this phenotype resembles the effect of phyB mutations on photoresponsiveness, indicating that both photoreceptors function in regulating seedling deetiolation in response to Rc. On the other hand, phyB phyC double mutants did not show any apparent decrease in sensitivity to Rc compared with phyB seedlings, indicating that the phyC mutation in the phyB-deficient background does not have an additive effect. These results suggest that phyB is necessary for phyC function. This functional dependence correlates with constitutively lower levels of phyC observed in the phyB mutant compared with the wild type, a decrease that seems to be regulated post-transcriptionally. phyC mutants flowered early when grown in short-day photoperiods, indicating that phyC plays a role in the perception of daylength. phyB phyC double mutant plants flowered similarly to phyB plants, indicating that in the phyB background, phyC deficiency does not further accelerate flowering. Under long-day photoperiods, phyA phyC double mutant plants flowered later than phyA plants, suggesting that phyC is able to promote flowering in the absence of phyA. Together, these results suggest that phyC is involved in photomorphogenesis throughout the life cycle of the plant, with a photosensory specificity similar to that of phyB/D/E and with a complex pattern of differential crosstalk with phyA and phyB in the photoregulation of multiple developmental processes.

As of this writing the Arabidopsis genome is 97% sequenced with only small portions of the highly repetitive regions within centromeres and telomeres remaining. The identification of approximately 25,000 plant genes will give plant biologists an opportunity to identify and understand the function of the proteins they encode. One exciting tool that will aid in this endeavor is the use of insertional mutagenesis to create "gene knockouts." The availability of a mutant line in which the action of a known, specific gene has been disrupted gives the plant biologist a powerful tool in understanding the action of that gene. The basis of this approach is to create a large population of plants containing randomly inserted pieces of foreign DNA. If the sequence of a gene is known, it is possible to devise a PCR-based strategy to identify a plant where that specific gene has been disrupted by the insertion of foreign DNA. To fully utilize this technology it is necessary to saturate the genome with insertion mutations and to develop efficient PCRbased screening methods to comb through knockout plant populations and identify specific mutant plants. The smaller the gene, the more difficult a target it represents, and thus hundreds of thousands of lines are needed to provide a high probability that a particular gene is present as a knockout in the population.As a beginning, a method has been developed for rapidly searching a large collection of T-DNA transformed Arabidopsis lines for the presence of T-DNA inserts within specific genes (Krysan et al., 1996(Krysan et al., , 1999. To use this technology, a collection of 60,480 Arabidopsis (accession Wassilewskija [WS]) lines were generated that were transformed with the T-DNA vector pD991. Preliminary data from screening this collection indicated that this collection could indeed be efficiently screened for mutant lines. To share this resource with all members of the Arabidopsis research community, a "Knockout Facility" was established at the University of Wisconsin (Madison) in 1999 as part of the Arabidopsis Functional Genomics Consortium. A detailed description of this initial population and the operation of the facility have been given in a recent publication (Krysan et al., 1999) and is described more fully at the website http://www. biotech.wisc.edu/Arabidopsis.In this brief note we will give an overview of the first year's operation and describe our future plans. We strongly advice that users read the web site fully before using the facility and contact us with any questions that they may have. CURRENT FACILITY OPERATIONThe facility is housed in the Plant Biotechnology Laboratory at the University of Wisconsin Biotechnology Center located at 425 Henry Mall, University of Wisconsin, Madison, WI 53706. The fee-for-service operation relies heavily on the administrative and information services of the Biotechnology Center. Users interact with the facility through the website. The site has a full description of the PCR screening including primer design and subsequent analysi...