Curcurbita pepo subspecies delineates striped cucumber beetle (Acalymma vittatum) preference.

The striped cucumber beetle (Acalymma vittatum (F.)) is a destructive pest of cucurbit crops, and management could be improved by host plant resistance, especially in organic farming systems. However, despite the variation in striped cucumber beetle preference observed within the economically important species, Cucurbita pepo L., plant breeders and entomologists lacked a simple framework to classify and exploit these differences. This study used recent phylogenetic evidence and bioassays to organize striped cucumber beetle preference within C. pepo. Our results indicate preference contrasts between the two agriculturally relevant subspecies: C. pepo subsp. texana and C. pepo subsp. pepo. Plants of C. pepo subsp. pepo were more strongly preferred than C. pepo subsp. texana plants. This structure of beetle preference in C. pepo will allow plant breeders and entomologists to better focus research efforts on host plant non-preference to control striped cucumber beetles.

Contrasting modes for loss of pungency between cultivated and wild species of Capsicum.

Studies documenting the inheritance of pungency or 'heat' in pepper (Capsicum spp.) have revealed that mutations at a single locus, Pun1, are responsible for loss of pungency in cultivars of the two closely related species Capsicum annuum and Capsicum chinense. In this study, we present the identification of an unreported null allele of Pun1 from a non-pungent accession of Capsicum frutescens, the third species in the annuum-chinense-frutescens complex of domesticated Capsicums. The loss of pungency phenotype in C. frutescens maps to Pun1 and co-segregates with a molecular marker developed to detect this allele of Pun1, pun1(3). Loss of transcription of pun1(3) is correlated with loss of pungency. Although this mutation is allelic to pun1 and pun1(2), the mutation causing loss of pungency in the undomesticated Capsicum chacoense, pun2, is not allelic to the Pun1 locus as shown by mapping and complementation studies. The different origins of non-pungency in pepper are discussed in the context of the phylogenetic relationship of the known loss of pungency alleles.

Development of sequence characterized amplified region (SCAR) primers for the detection of Phyto.5.2, a major QTL for resistance to Phytophthora capsici Leon. in pepper.

Phytophthora capsici causes devastating disease on many crop species, including Capsicum. Resistance in Capsicum annuum is genetically and physiologically complex. A panel of Capsicum germplasm that included genotypes from both C. annuum and C. chinense showing highly resistant, highly susceptible and intermediate or tolerant responses to the pathogen, respectively, was screened with a series of randomly amplified polymorphic sequence primers to determine which genomic regions contribute to the highest level of resistance. One primer, OpD04, amplified a single band only in those C. annuum and C. chinense genotypes showing the highest level of resistance. The amplified product was cloned, sequenced and used to design longer primers in order to generate a sequence characterized amplified region marker which was then mapped in a reference mapping population and a screened population segregating for resistance to P. capsici. These primers were observed to define a locus on pepper chromosome 5 tightly linked to Phyto.5.2, one of six quantitative trait loci (QTL) previously reported to contribute to P. capsici resistance. These results indicate that the Phyto.5.2 QTL may be widely distributed in highly resistant germplasm and provide improved resolution for this QTL. This work also defines the first breeding tools for this system, allowing for the rapid selection of genotypes likely to be highly resistant to P. capsici.

Second-site, intragenic alterations in the gene encoding subunit II of cytochrome c oxidase from yeast can suppress two different missense mutations.

Cytochrome c oxidase, a multi-subunit enzyme complex, accepts electrons from cytochrome c and transfers them to molecular oxygen to form water. Subunit II (Cox2p) of the enzyme complex provides the initial entry site for the electrons from cytochrome c. We report here the characterization of a yeast strain bearing a mutation in the gene encoding Cox2p which abolishes the activity of the enzyme complex. The alteration, at residue 163 in the yeast polypeptide, substitutes isoleucine for threonine and leads to loss of Cox2p and loss of the ability to carry out cellular respiration. We have also characterized 55 independent revertants of the mutant which have recovered the ability to respire. Of these revertants, 37 recover the ability to respire due to a compensatory alteration at residue 163, which produces either a wild-type threonine codon or one for valine or serine. The other 18 revertants recover function due to secondary changes at four different codons within the gene encoding Cox2p. Some of these second-site, intragenic revertants occur at sites significantly distant from the position of the original mutation. In addition, alterations at two of these sites have previously been shown to suppress a completely different missense mutation in the gene.

Analysis of strains of Saccharomyces cerevisiae with amino acid substitutions in the Cu(A)-binding region of subunit II of cytochrome c oxidase.

Cytochrome c oxidase accepts electrons from cytochrome c and transfers them to oxygen to form water. Electrons enter the complex through the Cu(A) site, formed by two copper atoms bound to mitochondrially encoded subunit II. The effect of amino-acid alterations in one of the Cu(A) ligands and in an amino acid adjacent to another of the ligands in the yeast enzyme is examined. Substitution of tyrosine for the Cu(A) ligand, cysteine 221, completely abolishes enzyme activity. In addition, 19 independent revertants of this mutant yeast strain recover function by restoring the cysteine codon. Replacement of a non-conserved glycine at position 228 by valine, adjacent to the Cu(A)-ligand histidine 229, virtually blocks enzyme activity. Activity is restored by inserting alanine or phenylalanine at position 228 or by amino-acid substitutions at nearby codons. Our results demonstrate that the Cu(A) ligand appears to be essential for enzyme function while other residues in the copper-binding region are less functionally constrained.