A phylogeny of Solanaceae is presented based on the chloroplast DNA regions ndhF and trnLF. With 89 genera and 190 species included, this represents a nearly comprehensive genus-level sampling and provides a framework phylogeny for the entire family that helps integrate many previously-published phylogenetic studies within Solanaceae. The four genera comprising the family Goetzeaceae and the monotypic families Duckeodendraceae, Nolanaceae, and Sclerophylaceae, often recognized in traditional classifications, are shown to be included in Solanaceae. The current results corroborate previous studies that identify a monophyletic subfamily Solanoideae and the more inclusive "x = 12" clade, which includes Nicotiana and the Australian tribe Anthocercideae. These results also provide greater resolution among lineages within Solanoideae, confirming Jaltomata as sister to Solanum and identifying a clade comprised primarily of tribes Capsiceae (Capsicum and Lycianthes) and Physaleae. Stronger evidence also is provided for the inclusion of Capsicum within a paraphyletic Lycianthes. Solanaceae are a predominantly New World group, with several lineages represented on other continents. Apart from events within Solanum (for which sampling in this study is inadequate for biogeographic interpretations) the Old World representatives of Solanaceae can be accounted for by eight or nine dispersal events.

Plant genomes encode large numbers of nucleotide-binding, leucine-rich repeat (NB-LRR) proteins, many of which are active in pathogen detection and defense response induction. NB-LRR proteins fall into two broad classes: those with a Toll and interleukin-1 receptor (TIR) domain at their N-terminus and those with a coiled-coil (CC) domain at the N-terminus. Within CC-NB-LRR-encoding genes, one basal clade is distinguished by having CC domains resembling the Arabidopsis thaliana RPW8 protein, which we refer to as CCR domains. Here, we show that CCR-NB-LRR-encoding genes are present in the genomes of all higher plants surveyed, and that they comprise two distinct subgroups: one typified by the Nicotiana benthamiana N-required gene 1 (NRG1) protein and the other typified by the Arabidopsis activated disease resistance gene 1 (ADR1) protein. We further report that, in contrast to CC-NB-LRR proteins, the CCR domains of both NRG1- and ADR1-like proteins are sufficient for the induction of defense responses, and that this activity appears to be SGT1-independent. Additionally, we report the apparent absence of both NRG1 homologs and TIR-NB-LRR-encoding genes from the dicot Aquilegia coerulea and the dicotyledonous order Lamiales as well as from monocotyledonous species. This strong correlation in occurrence is suggestive of a functional relationship between these two classes of NB-LRR proteins.

Plant genomes encode large numbers of nucleotide binding and leucine-rich repeat (NB-LRR) proteins, some of which mediate the recognition of pathogen-encoded proteins. Following recognition, the initiation of a resistance response is thought to be mediated by the domains present at the N termini of NB-LRR proteins, either a Toll and Interleukin-1 Receptor or a coiled-coil (CC) domain. In order to understand the role of the CC domain in NB-LRR function, we have undertaken a systematic structure-function analysis of the CC domain of the potato (Solanum tuberosum) CC-NB-LRR protein Rx, which confers resistance to Potato virus X. We show that the highly conserved EDVID motif of the CC domain mediates an intramolecular interaction that is dependent on several domains within the rest of the Rx protein, including the NB and LRR domains. Other conserved and nonconserved regions of the CC domain mediate the interaction with the Ran GTPaseactivating protein, RanGAP2, a protein required for Rx function. Furthermore, we show that the Rx NB domain is sufficient for inducing cell death typical of hypersensitive plant resistance responses. We describe a model of CC-NB-LRR function wherein the LRR and CC domains coregulate the signaling activity of the NB domain in a recognition-specific manner.